Systems and Operations Management Essay Example | Topics and Well Written Essays - 2000 words - 1

Systems and Operations Management - Essay Example The main importance of such strategies is to ensure that the relationship with customers is enhanced in order to improve the processes of sales and marketing. Nonetheless, the lack of or presence of internet security is likely to be a major topic of discussion among different countries as well as in a large number of corporations (Peng, 2008). Part One: Option 4 Summary of the text; Achieving Operational Excellence and Customer Intimacy Technology has been extensively applied in transforming the shape of marketing as is used in different organizations. However, with the development and implementation of these advanced technologies a number of changes are experienced within the operational functions of the business. There is thus need to safeguard and protect the information systems, data as well as other information technologies. In this chapter, the major processes associated with advanced technology in the form of online and internet use of the computer is highlighted. The number o f challenges is depicted to be related to Facebook whose users are warned to watch out. In relation to this, there have been a number of reported cases related to theft and presence of malicious software. These are associated with spam, malware as well as other serious security issues. With time, several destructive elements have been introduced into these systems. Similarly to the other viruses circulating within the computer system, these areas were faced with the introduction of Koobface worm in December 2008, the 18 month hacker scam for passwords, which resulted in the entry of the Trojan horse. It is as a result of this that financial data was stolen around the year 2009. The other main challenge was the emails that were created in May 2010 with an intention of stealing logins (Laudon & Laudon, 2013). In comparison to other online tools such as e-mails social sites and especially Facebook is shown as the main target that is used by hackers. It has been related to a high gullib ility level of the users. This is despite the high security measures that have been placed by its dedicated team to include up-to-date measures. The hackers thus make use of â€Å"social engineering† malicious software to develop the attacks aimed at the consumers. As such, it is indicated that there main activities include the theft of passwords and data as well as using botnets. As Laudon and Laudon indicate, it is because of this that different organizations are faced with the task of constantly developing advanced security policies. This is done through the people who include stakeholders within the organization. With this, the organization and specifically its management are presented with the duty to deploy a serious security team to ensure that security is always maintained. These have to be achieved through the application of current technological advancements. They may include the implementation of the website security system, technology that is able to authenticate and security technologies that are applied on an individual basis (2013). The most appropriate way to attain this is through the identification of most of the malicious codes normally used, to identify the different sources of spam and to protect user data. All this is stated as the effort towards responding while making use of the information systems and operations. As such, these steps enhance the action towards providing a number of business solutions since

Midsummer Nights Dream by Shakespeare Essay Example for Free

Midsummer Nights Dream by Shakespeare Essay A Midsummer Nights Dream by William Shakespeare frequently explores the complex types of love. Love is timeless subject. It will forever be the theme of much popular entertainment and the source of conflict for many men and women. No one understands the theme of love greater than Shakespeare and therefore I will look at how conflict is developed through love in Midsummer Nights Dream At the start of the play, Shakespeare explores the theme of love through the characters Theseus and Hippolyta. Theseus seduces Hippolyta. I wound you with my sword and one by love The quote shows the conflict caused by love between Theseus and Hippolyta in form of a battle. Shakespeares purpose was to introduce the idea that love involves conflict through this scene. The audience begins to engage with the theme of love as it creates crises to the plot. This idea that love involves conflict is developed when Hermia and Lycander are bought in front of Theseus. Hermia wishes to marry her romantic love Lysander but her father Igneus has power over her as by law and paternal love. Shakespeare presents for us the conflict between eternal and romantic love. The course of true love never went so smooth-Lysander. This quote proves that love brings hard times and conflicts during its timeless life. The audience develops the theme of love and the conflict that can be caused by inter-relation of love. The conflict between relations of love is developed further as Helenas love for Demetrius is not returned to her but to her best friend Hermia. Shakespeare shows how the platonic love between Helena and Hermia suffers due to Helenas obsessive love towards Lysander and Hermias romantic love for Lysander. Sickness is catching, yours would I catch!-Helena to Hermia. The effect of this is that the audience presents himself/herself to believe if one love blooms, the other may suffer. In the middle of the play the conflict between love through reason and blind  love are clearly shown through characters Bottom and Titania. Titania, under the influence of the magic potion symbolizes love at first sight and falls in love with Bottom while Bottom symbolizes love for reason and fails to see why she loves him. Truth, reason, and love keep little company these days Through the quote Bottom describes the conflict which the two types of love have in that blind love masks and hides all reasons of love. Shakespeare shows the nonsense and humor of love at first sight. Conflicts in love in Midsummer Nights Dream are resolved in all happy endings; Theseus marries Hippolyta, 4 nobles married. This is where Shakespeare loses his reality because it is a play. A conflict caused by love lasts for a lifetime in reality but a play must end in with a happy ending as it is purely for entertainment and therefore Shakespeare finishes this way. We can argue that Shakespeare may have done this to show that loves other than reason are more common than reason. The theme of love causes many conflicts. It breaks friendships, paternal love, and romantic love. Even if the love is strong it can be broken. Shakespeare persuades audience that love for reason is less common but it is better for all the right reasons. Shakespeare uses love between characters to develop conflicts throughout A Midsummer Nights Dream

Bob Marley: Legend :: essays research papers

The question isn't how long are we going to live on this earth; it is how much are we going to live on this earth. In his 36 short years, Bob Marley achieved more than most who live to a so-called ripe old age. Bob once said, "My life is only important if mi cyan help plenty people. My life is for people. That's who mi is." He lived on earth but thought the thougthts of heaven. In his song "Rastaman Vibration" Marley implores us to look out for each other. "Why not help one another along the way and make it much easier." Funkmaster George Clinton once said that Bob Marley "was one of those people who wasn't on anybody's side in particular. He was on everybody's side. And that's scary to the system." Bob told us to "open your minds and look within; are you satisfied with the life you're living?" He urged us to wake up, to arise from our sleep and slumber, as there's work to be done. And that, too, is scary for the system. In support of any Messiah, there are at least 12 apostles. In the case of Bob Marley, there is an undisclosed number of disciples whom he chose to send forth and preach the (reggae) gospel in this time. In addition to members of his Wailers band and I-Threes, he left behimd a family full of messengers. His beloved mother, Cedella Marley Booker, is the inspiration for the Bob Marley Caribbean Festival and founder of The Movement of Jah People. This organization is carrying out the dreams and goals of her son who always looked out for the underprivileged and down-trodden. Ms. Booker lives in the house Bob bought her in Miami, the spacious yard where he came to chill-out from his rigorous and demanding schedule. He once said, "This peace work, it don't stop. We, the youth, got a job to do." His younger brother, Richard Booker, is at the helm of the movement and ably acts as his mother's right hand man. Bob's sister, Pearl Livingston, is among the family members who perform each year, along with their cousins Gloria, Lorraine and Jimmy. Marley stated that "not one of my seed shall sit on the sidewalk and beg bread." Bob's children include Ziggy, Stephen, Cedella, Sharon, Damian, Julian, Kymani, Rohan and Robert. His grandchildren include Daniel, Justice, Zouri, Joseph, Stephan, Huon, Jacob, Soul Rebel, Kaya, Kymani Jr.

Marianne Boruchs Year in Hawaii :: Marianne Boruch Year Hawaii Essays

Marianne Boruch's Year in Hawaii In her poem, â€Å"Year In Hawaii,† Marianne Boruch effectively portrays the feeling of an endless, motionless setting. This lyric poem attempts to transcend time by working with timelessness. The key lines to the poem take place at the very beginning, â€Å"The ocean takes so long/to think about.† Immediately the reader is met with mixed sensations of timelessness as well as restlessness. There’s a dreamy, sluggish feel to her wording. Using the ocean is perfect for evoking this, as looking out at the water, â€Å"Distance stops; one sees the endless line/of something.† So much empty space rolling out and out until it meets the sky. Boruch goes on to make her stance even clearer, â€Å"I was a toad/there, a river thing that got lost.† She places herself as a small, tiny creature that has no grasp of how big its surroundings are. After setting the mood in this tropical haven, Boruch makes a point to explain, â€Å"I never had a vision/about the place. I never thought: this/is the beginning of the world.† Boruch lets the reader know this is not a dream world, this is not something that can be conjured up in the mind and cradled whenever desired. Her time in Hawaii is something that she could have never imagined. This helps the flow of the poem, as she then depicts how easily pleased humans are. â€Å"You’ve seen/the postcards. People buy them thinking/everything worthwhile comes/through a camera lens, and they put them/in a pocket or down the dark throat/of a mailbox someone later opens/with a key.† Finding themselves in this unimaginable tropical island, humans try to capture the unexplainable on a piece of paper and bring it home to their safe comforts. Going back to the running theme of restlessness, Boruch portrays the human desire to be able to see the beauty of this landscape and the resulting unawareness of how unattainable it is. Amazed, they get there and think it is a material thing, believing that a simple postcard will do justice to their paradise. Even though she seems to be depicting a ‘paradise’ mind, Boruch immediately switches over to an ‘everyday’ mind. She describes the natives, â€Å"wanting just to live there, thank you,/going off to work and coming back, normal/things.† It’s as though the natives bring the poem back into time again, while the tourists had been stuck in timelessness.

Ethical Decision Making Essay

Abstract What is ethics and what place does it have in decision-making? Ethics means different things to each of us. We develop our ethics from our culture, ethnic background, religious beliefs and all that make us unique as humans. Knowing this does not help when we are asked as administrators or managers to make decisions that are jam-packed with ethical dilemmas. Acting as Faith Community Hospital (FCH) administrator I turned to the Santa Clara University website, article â€Å"A Framework for Ethical Decision Making†. This article gives five steps that I will use to address the problems FCH face. They are: Recognize a moral issue, Get the facts, Evaluate the alternative actions from various moral perspectives, Make a decision, Act, then reflect on the decision later. Ethical Decision Making Trying to determine the meaning of ethics is, to say the least, a challenge. My search for that meaning took me to the Santa Clara University website. There I found discussions that I agreed with. Sociologist Raymond Baumhart found that replies to the question â€Å"What does ethics mean to you?† was as diverse as those he asked. The answers varied from personal feelings to what is socially acceptable, from religion to legality. So then, what does it mean to be ethical in your decision-making? Shanks tell us â€Å"because we have the ability to be critical of our interpersonal behavior . . . . . we have the ability to develop codes and norms to guide that behavior. Those moral norms and codes, plus a set of virtuous character traits, are what we mean when we talk about ethics.† He also tells us that while we all endeavor to make ethical decisions we run into â€Å"stumbling  blocks† inhibiting our ethical decision-making. He lists the following: -â€Å"My small effort won’t really make a difference -People may think badly of me -It’s hard to know the right thing to do -My pride gets in the way -It may hurt my career -It just went by too quickly -There’s a cost to doing the right thing† We’ve all had to face these â€Å"stumbling blocks†. This is why ethical decision-making is so personal and varied. In our case study of Faith Community Hospital we came across many issues needing resolution. The majority if not all of them required ethical decision-making. Faith Community had a diverse group of employees, and each of them had their own set of ethical/moral standards. While administration can appreciate those differences, the responsibility to bring unity to the organization falls to them. Putting my self in the role of administrator, how do I accomplish this task? Again, I turn to the Santa Clara University website, to the article â€Å"A Framework for Ethical Decision Making†. This article gives five steps that I will use, they are: 1.Recognize a moral issue 2.Get the facts 3.Evaluate the alternative actions from various moral perspectives 4.Make a decision 5.Act, the reflect on the decision later First, recognize a moral issue. At Faith Community there are several issues. They are: -Staff on both ends of the spectrum of Do Not Resuscitate (DNR) orders. I have staff that resuscitate when a DNR is in place as well as staff that do not resuscitate when a DNR is not in place. -Staff refusing treatment to patients without first confirming insurance coverage as well as requiring HIV clearances. -Unauthorized pro bono treatment and installment payments on prescriptions. -Unnecessary treatments being performed Second, get the facts. To some extent the facts speak for themselves. Staff is acting on their individual code of ethics without regard or possibly without knowledge of the hospital’s code. With respect to the DNR issues, in all cases the family members were happy, but in this case, as administrator their happiness is not the issue. The legality however is. DNR orders are for the protection of the hospital and its staff. If they are not adhered to that protection is none existent. What are the facts surrounding treatment or lack thereof? Investigation again reveals varied results. I have staff that fear for their personal safety, so they require HIV clearance before treatment. I have staff that is concerned for the welfare of the hospital, so they require insurance verification prior to treating. I have staff that care for the patients themselves so much they provide free service or payment on installments, both occurring without consent of administration. I also have staff the order treatment just for the sake of doing the procedure. Third, evaluate the alternative actions from various moral perspectives. While the hospital mission â€Å"to promote the health and well-being of the people in the communities we serve† must remain a focal point, as administrator the overall health of the organization falls to me. The decision on what treatment should be given should be at the discretion of the physician. The physician must not abuse this authority by ordering those treatments that are not necessary for the welfare of the patient. Even though I can appreciate and even respect the values presented by the staff the truth of the situation is that not everyone is going to be happy. What is going to â€Å"promote the common good† for all concerned? This becomes the question to answer. Fourth, make a decision. The number decision is the development of policies and procedures that address the identified issues. With regard to: -DNR orders: Once the policy is written concerning implementation of DNR orders, staff in positions to implement these orders will receive written copies of the policy at a mandatory training session. Each staff member will also be required to sign and acknowledgement form indicating receipt of the policy and personal accountability should policy not be adhered to. -Refusal to treat. In addition to the newly developed policies and procedures a new department will be created. The sole function of this department is to determine insurance eligibility. If the patient does not have insurance, it will be determined if they are eligible for state or federal aide. If it is determined they are rejected in both arenas and their injuries are not life threatening, they will not be treated. Training will be held to address both insurance issues and personal safety issues. -Treatment in general. All staff will be required to sign an acknowledgement as to hospital policy regarding non-emergency treatments. This policy will address: unnecessary procedures, when and if pro bono services will be allowed, as well as acceptable financial agreements with the hospital. Fifth, act, and then reflect on the decision later. Consistent reevaluation  of all new policies will be essential. Through their monitoring, I will be able to identify problem areas as they arise and fine-tune the process to deal with them. The decision making process is constant. In order to maintain the health of an organization the process must remain fluid. This is mandated by the one constant in every workplace. THINGS CHANGE! Conclusion Utilizing the five steps outlined in the Santa Clara University website, article â€Å"A Framework for Ethical Decision Making†, allowed Faith Community Hospital to benefit from a good ethical decision. While all concerned my not is happy with the outcome, the guesswork has been eliminated providing for more consistent and I believe better treatment for the community being served by FCH. Training will be ongoing, as will the evaluation of the decision making process, allowing for changes to be made quickly. References A Framework for Ethical Decision Making. Retrieved April 21, 2002 from the World Wide Web: http://www.scu.edu/SCU/Centers/Ethics/practicing/decison/framework.html What is Ethics? Retrieved April 21, 2002 from the World Wide Web: http://www.scu.edu/SCU/Centers/Ethics/practicing/decison/whatisethics.html Shanks, T. Everyday Ethics. Issues in Ethics- V.8, N.1. Retrieved April 21, 2002 from the World Wide Web: http://www.scu.edu/SCU/Centers/Ethics/publications/iie/v8n1/everydayethics.html

Kra canal

Kra canal The discussions of the opening of the kra canal1677 The Kra Canal was first proposed on this year,during the reign of King Narai the Great1793 project was revived by King Ramai's brother in during the early Rattanakosin period.1858 King Rama III revived the project again.1872-1882 It was followed by King Rama V.1917 Next came King Rama VI, who looked at the project.1960 The project was proposed by big businessman Chao Chaokwanyuen.1982 Proposals from Admiral Amorn Sirikaya, Chumphol Silpa-archa and Yupha Udomsak.The Nation, September 8, 2001KRA CANAL PROPOSAL: Revival of dream urgedMinistry says full feasibility study should be launchedMalaysia backs canal go-ahead - Bangkok Post, May 10, 2002The canal would be good for the region, even though Malaysia's own port business would suffer if it went ahead, Mr Mahathir told him. The project, which has been on and off the drawing board for many decades, became Gen Chavalit's political canvassing manifesto.King Rama VI Monument at Lumphini Park, Bangkok. T...Chinese and Malaysian firms were keen to invest in the project, which was expected to take seven years and cost 800 billion baht. The feasibility study alone is costing the government 1.8 billion baht.Finding out about Phuket Pass Project Limited - February 15, 2003Phuket Pass Project Limited is the company that was given the contract for the expensive study of the Kra Canal Project. It first surfaced in the news on August 8, 2002 when it was reported the company would receive the canal study project.The embarrassing Kra canal saga - July 7, 2003The question of whether a canal is viable or not continues to be a moot point as the continuing murky subject of the expensive study drags on.July 6, 2003PPP was awarded the contract on Jan 17 by the national...

jane eyre childhood essays

jane eyre childhood essays HOW DOES OUR CHILDHOOD EXPERIENCES AFFECT OUR LIVES Certainly every experience we have not only in our childhood but also in our entire life affects it either in a positive or a negative way. Experiences in our childhood are more important because those are the ones that bring up our character and personality. We have to learn to distinguish which effects of our experiences are good for our lives and try to change the ones that are not. There are experiences that change our lives in a critical way. Those experiences are most of the time sad and traumatic. In my opinion, there is always something or someone that can help us with those traumas. Most of the time effects are all kind of fears that we have to learn to beat. We have to learn to change every bad effect caused by a negative experience. The same experience will never cause the same effect in two different persons. People change in a different way depending on their personality and character. Some people are stronger that other and bear more pressure, some people do not care about certain subjects and sometimes do not pay attention to things that happen. Something we all can do is learn from those experiences even it they are negative. That way, we will always take something good of every experience. We dont have to blame our sad and negative experiences and justify our bad character and actions. It is very easy to blame childhood experiences to justify our character, but it is not the right thing to do. We have to be sincere with everyone and mostly with ourselves. A good way to start is looking at our faults and try to change them, not look at the cause because it is already past. All we need is to have the intention and the disposition to do it. It is very important that we dont blame our experiences, but try to learn from them. Because we know every experience will affect us, either a negative or a positive one, we have to learn to alwa...

Simon Bolivars Crossing of the Andes

Simon Bolivar's Crossing of the Andes In 1819, the War of Independence in Northern South America was locked in a stalemate. Venezuela was exhausted from a decade of war, and patriot and royalist warlords had fought each other to a standstill. Simà ³n Bolà ­var, the dashing Liberator, conceived of a brilliant yet seemingly suicidal plan: he would take his 2,000 man army, cross the mighty Andes, and hit the Spanish where they were least expecting it: in neighboring New Granada (Colombia), where a small Spanish army held the region unopposed. His epic crossing of the frozen Andes would prove to be the most genius of his many daring actions during the war. Venezuela in 1819 Venezuela had borne the brunt of the War of Independence. Home of the failed First and Second Venezuelan Republics, the nation had suffered greatly from Spanish reprisals. By 1819 Venezuela was in ruins from the constant warring. Simà ³n Bolà ­var, the Great Liberator, had an army of some 2,000 men, and other patriots like Josà © Antonio Pez also had small armies, but they were scattered and even together lacked the strength to deliver a knockout blow to Spanish General Morillo and his royalist armies. In May, Bolà ­vars army was camped near the llanos or great plains, and he decided to do what the royalists least expected. New Granada (Colombia) in 1819 Unlike war-weary Venezuela, New Granada was ready for revolution. The Spanish were in control but deeply resented by the people. For years, they had been forcing the men into armies, extracting â€Å"loans† from the wealthy and oppressing the Creoles, afraid they might revolt. Most of the royalist forces were in Venezuela under the command of General Morillo: in New Granada, there were some 10,000, but they were spread out from the Caribbean to Ecuador. The largest single force was an army of some 3,000 commanded by General Josà © Marà ­a Barreiro. If Bolà ­var could get his army there, he could deal the Spanish a mortal blow. The Council of Setenta On May 23, Bolà ­var called his officers to meet in a ruined hut in the abandoned village of Setenta. Many of his most trusted captains were there, including James Rooke, Carlos Soublette and Josà © Antonio Anzotegui. There were no seats: the men sat on the bleached skulls of dead cattle. At this meeting, Bolà ­var told them of his daring plan to attack New Granada, but he lied to them about the route he would take, fearing they would not follow if they knew the truth. Bolà ­var intended to cross the flooded plains and then cross the Andes at the Pramo de Pisba pass: the highest of three possible entries into New Granada. Crossing the Flooded Plains Bolà ­var’s army then numbered some 2,400 men, with less than one thousand women and followers. The first obstacle was the Arauca River, upon which they traveled for eight days by raft and canoe, mostly in the pouring rain. Then they reached the plains of Casanare, which were flooded by the rains. Men waded in water up to their waists, as thick fog obscured their vision: torrential rains drenched them daily. Where there was no water there was mud: the men were plagued by parasites and leeches. The only highlight during this time was meeting up with a patriot army of some 1,200 men led by Francisco de Paula Santander. Crossing the Andes As the plains gave way to the hilly jungle, Bolà ­var’s intentions became clear: the army, drenched, battered and hungry, would have to cross the frigid Andes Mountains. Bolà ­var had selected the pass at Pramo de Pisba for the simple reason that the Spanish did not have defenders or scouts there: no one thought an army could possibly cross it. The pass peaks at 13,000 feet (almost 4,000 meters). Some deserted: Josà © Antonio Pez, one of Bolà ­vars top commanders, tried to mutiny and eventually left with most of the cavalry. Bolà ­vars leadership held, however, because many of his captains swore they would follow him anywhere. Untold Suffering The crossing was brutal. Some of Bolà ­var’s soldiers were barely-dressed Indians who quickly succumbed to exposure. The Albion Legion, a unit of foreign (mostly British and Irish) mercenaries, suffered greatly from altitude sickness and many even died from it. There was no wood in the barren highlands: they were fed raw meat. Before long, all of the horses and pack animals had been slaughtered for food. The wind whipped them, and hail and snow were frequent. By the time they crossed the pass and descended into New Granada, some 2,000 men and women had perished. Arrival in New Granada On July 6, 1819, the withered survivors of the march entered the village of Socha, many of them half-naked and barefoot. They begged food and clothing from the locals. There was no time to waste: Bolà ­var had paid a high cost for the element of surprise and had no intention of wasting it. He swiftly refitted the army, recruited hundreds of new soldiers and made plans for an invasion of Bogota. His greatest obstacle was General Barreiro, stationed with his 3,000 men at Tunja, between Bolà ­var and Bogota. On July 25, the forces met at the Battle of Vargas Swamp, which resulted in an indecisive victory for Bolà ­var. The Battle of Boyac Bolà ­var knew that he had to destroy Barreiros army before it reached Bogota, where reinforcements could reach it. On August 7, the royalist army was divided as it crossed the Boyaca River: the advance guard was in front, across the bridge, and the artillery was far to the rear. Bolivar swiftly ordered an attack. Santanders cavalry cut off the advance guard (which were the best soldiers in the royalist army), trapping them on the other side of the river, while Bolà ­var and Anzotegui decimated the main body of the Spanish force. Legacy of Bolà ­var’s Crossing of the Andes The battle lasted only two hours: at least two hundred royalists were killed and another 1,600 were captured, including Barreiro and his senior officers. On the patriot side, there were only 13 killed and 53 wounded. The Battle of Boyac was a tremendous, one-sided victory for Bolà ­var who marched unopposed into Bogota: the Viceroy had fled so swiftly that he left money in the treasury. New Granada was free, and with money, weapons, and recruits, Venezuela soon followed, allowing Bolà ­var to eventually move south and attack Spanish forces in Ecuador and Peru. The epic crossing of the Andes is Simà ³n Bolà ­var in a nutshell: he was a brilliant, dedicated, ruthless man who would do whatever it took to free his homeland. Crossing flooded plains and rivers before going over a frigid mountain pass over some of the bleakest terrain on earth was absolute madness. No one thought Bolà ­var could pull off such a thing, which made it all the more unexpected. Still, it cost him 2,000 loyal lives: many commanders would not have paid that price for victory. Sources Harvey, Robert. Liberators: Latin Americas Struggle for Independence Woodstock: The Overlook Press, 2000.Lynch, John. The Spanish American Revolutions 1808-1826 New York: W. W. Norton Company, 1986.Lynch, John. Simon Bolivar: A Life. New Haven and London: Yale University Press, 2006.Scheina, Robert L. Latin Americas Wars, Volume 1: The Age of the Caudillo 1791-1899 Washington, D.C.: Brasseys Inc., 2003.

The Existence of Plate Tectonics on Mars Essay Example | Topics and Well Written Essays - 2500 words

The Existence of Plate Tectonics on Mars - Essay Example However, observations of the planet's current state shows Mars at much higher level of deterioration that that of Earth. NASA's latest Mars project, Phoenix, made a successful landing on Mars and spent five months collecting data that has yet to be fully analyzed on the planet's climate, soil, and atmosphere. This mission yielded further proof that there was a type of water on or near the surface of Mars. Soil samples collected prove that there could have once been sustainable life on the planet (Cowing). There have also been findings in recent years suggesting that Mars once had a molten inner core, much like our own. The presence of stripes along the crust layer of Mars, believed to be formed from the crust renewing itself through use of the molten core, lends further proof to the idea that there were once tectonic plates resembling those of Earth (Cain). "The theory of plate tectonics is based on the movement of rigid plates on the planet's surface. Plates are bounded a ridge wher e new crust is created, a trench or subduction zone, where the crust is consumed, and transform faults, along which plates slip" (Connerney, et al. 2005, p. 4). The question as to the existence of tectonic plates on Mars remains a very highly debated issues among scientists. In its current state, Mars is essentially a dead planet, meaning there is no life present and little to no activity on behalf of the planet itself. The lakes and riverbeds have dried up and what is left of the atmosphere is being blown away in chunks by massive wind shears (Cain). Though it is believed that Mars could have once supported life, that seems virtually impossible now. New theories are supported by scientific evidence which suggest that the layers of Mars once greatly resembled the layers of Earth, including a molten core, tectonic plates, and a changing crust layer. It is believed that the molten core of the planet slowly cooled, leaving the stripes currently observable in the hardened crust. Proof of the tectonic plates was recorded by NASA's Mars Global Surveyor in a 1999 (NASA Press Release). While the initial findings only showed the striping of Mar's magnetic field in the southern hemisphere, new data shows that the magnetic field covers the entire surface of the pl anet in a pattern similar to that of Earth (NASA Status Report).(NASA/JPL) Along the striped lines of the magnetic field there are also fault formations and other geographic signs that point toward the existence of a tectonic plate system similar to that of our own planet. As an example of this, the Tharsis volcanoes on Mars are actually aligned in a straight line and it is now believed that, like the Hawaiian Islands, these volcanoes formed over a hot spot in the mantle (Cain). Fault formations, similar to the Martian ones, can only be formed by tectonic plates shifting, pushing new molten crust up from the planet's mantle and changing magnetic polarity of the area as it hardens (Cain). Unfortunately an exhaustive analysis of the geology of Mars has yet to be conducted. Therefore many of the currently accepted theories of the inner workings of the planet are based on what has been observed and studied on Mars combined with what is known about its sister planet, Earth. Whatever plate tectonics previously existed on

Week 7 lab on human bones Report Example | Topics and Well Written Essays - 750 words

Week 7 on human bones - Lab Report Example Locate the spine and palpate along the edges with the subject recumbent, bony prominences would be felt. Easier in children and lean males (Sinnatamby). C7: relatively harder to locate and palpate, easier in adult, lean males, feels as the most prominent cervical spinous process, differentiated from C6 by its movement upon extension of the head (Sinnatamby). Curves of the spine: easy to locate and palpate in children and lean males, with the subject standing erect. Just following the spine would reveal its curves in the cervical, thoracic, lumbar, sacral, and coccygeal regions, the last two regions being harder to locate and palpate (Drake, Vogl, and Mitchell). Several ribs: the upper ribs are easier to locate in males than in females, and overall easier to locate in lean people. They feel as bony arches alternating with shallow depressions (Moore). The sternocostal junction: once the sternum is located, the sternocostal junction is easy to locate by palpating at the edge of the body of the sternum, easier in lean males (Sinnatamby). Posterior to anterior palpation of ribs: relatively difficult to palpate individual ribs posteriorly than anteriorly. Easier in lean males. Start from the sides of the thorax and palpate along the arches till the body of the sternum (Drake, Vogl, and Mitchell). The 12th rib: relatively hard to locate. First locate the xiphoid process which is hard to palpate itself, then move along the edge to the hanging ribs. Tender in children. Much easier to locate in lean males (Moore). Jugular notch on manubrium: easier to locate, felt as a dip or a notch medially at the junction of the two clavicles. Easier in

High Aspect Ratio Pholithography for MEMS Application Article

High Aspect Ratio Pholithography for MEMS Application - Article Example This is the most prominent technique and is widely used and can be used with tall microstructures in the range of 100 micrometers to 1 mm. This method though resulting into long micro structures does not affect the lateral dimension accuracy making it effective method in achieving this objective. However, the method cannot be universally applied due to lack of a synchronized source and the fabrication cost of LIGA that is prohibitive. The use of X-rays from a synchronized source with the capability of giving high intensity, hard x-rays with low divergent properties, makes this method to achieve great results despite these limitations. This led to the development of low cost and commonly available process that would meet the above objectives, and that is close to LIGA. An example was the reactive ion Etching (RIE) of polyamide, which has been presented as a method that could fabricate high aspect ratios structures at the lower costs compared to the above process. This was able to achi eve a thickness so of more than 100 micrometers, and an aspect ratio of about 10. This process was however found to be more tedious as it required modification of the RIE machine, and hence not effective. Other methods that have been used to investigate in this process include the photosensitive polyamide together with UV exposure and have been used in fabricating plating molds. This process achieved a thickness of up to 50 micrometers and an aspect ratio close to 8. Other methods that have been investigated include the high aspect commercial photolithography with photoresist and a near UV light source, in fabricating high aspect ratio molds of metal structures. These are some of the motivations behind the research above by Miyajima and Mehregany. Research background The research involved investigating the fabrication of high-aspect-ratio structures using a commercially available positive photoresist and the UV exposure increasing molds, which would be used together with electroless nickel plating. The research involved an effort to maintain a 2- 3micrometers line width and increasing the photoresists thickness altogether. This was the main point that most of the LIGA high-aspect-ratio process as described above ignored. Using an electrostatic actuator that had been micro machined with 1.5 micrometers wide active gaps and up to 5 micrometers polysilicon, and increasing the gap side wall height instead of increasing the gap height was found to result to reduced force/torque, and this eliminated the urge to use high aspect ratio structures. This was the remarkable difference in this process as compared to other processes investigating this problem. The use of evaporated solvents during the coating process ensured that films thicker than 8 micrometers were obtained. After carrying out the complete process and the patterns in photoresist, electroless nickel plating was performed to fabricate metal structures, and this required the chemical compatibility of the pho toresits with the plating chemicals to be an important considerations. This photo lithography process was found to be compatible with the electroless nickel plating process described above. Methodology One of the variables that were to be considered and regulated is the spin speed in coating. A slower speed below 1000rpm could have resulted to rough surface in the photoresists and the

In a well-developed essay of 3-5 pages examine the role of the

In a well-developed of 3-5 pages examine the role of the protagonist in these three novels - Essay Example By contrast Twain’s Huck has weak family ties yet he too must reconcile his own personal desires and choices with those mandated by society. In each novel the authors use literary elements such as characterization, point of view and conflict to demonstrate how these young protagonist face these challenges and development a poignant sense of self-awareness. Emma’s protagonist Emma Woodhouse, is a young woman of means and influence. Although societal norms dictate that Emma, as a female of status is required to marry well she shows independence in her resolve not to do but chooses instead to interfere in the lives of others by playing matchmaker for them. When Emma’s matchmaking focuses on manipulating the love life of 17 year old Harriet Emma’s own life takes a turn toward maturity and growth. Emma’s initial goal was to make Harriet a better woman and decides that her current love interest Martin who is a farmer, will not factor into her plans for Harriet. To this end she introduces Harriet to Mr. Eton a Vicar whom she thinks is a better match for Harriet. Things go horribly wrong for Emma when Mr. Elton proposes to her instead and his conduct is not what Emma would have expected of him at all. This is just the start of Emma’s growth and maturity because as she learns more about people’s peculi arities she learns more about herself and in the process falls in love and learns a measure of humility as a result. The Adventures of Huckleberry Finn chronicles the adventures and growth Huck who is a young independent boy with both strength and stamina of character. Huck’s strength and character are tested early on when his father who is an alcoholic and violent returns to town and kidnaps him and holds him against his will. Huck’s independence and strength is demonstrated when manages to escape by faking his death following which he goes on the run with runaway slave Jim. My Name is

CoverGirl Cosmetics Research Paper Example | Topics and Well Written Essays - 500 words - 1

CoverGirl Cosmetics - Research Paper Example ed by any organization would influence the financial ratios and therefore business objectives would also be reflected in the financial ratios of the organization. For instance, if an organization is expanding its business and trying to improve its profitability then the financial ratios would reflect an improvement in profit margin, operating margin as well as other ratios that are used to measure the productivity and profitability of the company. Three most important ratios for organizations are operating margin, net profit margin and total assets turnover. CoverGirl Cosmetics is the company selected for this report and as the company is a business unit of Procter and Gamble therefore financial statement of P&G’s beauty division has been used to calculate the financial ratios. In order to calculate the industry average ratios; two firms have been selected besides CoverGirl Cosmetics and these firms are Revlon and L’oreal. The following table shows the important financial figures required to calculate three

In a well-developed essay of 3-5 pages examine the role of the

In a well-developed of 3-5 pages examine the role of the protagonist in these three novels - Essay Example By contrast Twain’s Huck has weak family ties yet he too must reconcile his own personal desires and choices with those mandated by society. In each novel the authors use literary elements such as characterization, point of view and conflict to demonstrate how these young protagonist face these challenges and development a poignant sense of self-awareness. Emma’s protagonist Emma Woodhouse, is a young woman of means and influence. Although societal norms dictate that Emma, as a female of status is required to marry well she shows independence in her resolve not to do but chooses instead to interfere in the lives of others by playing matchmaker for them. When Emma’s matchmaking focuses on manipulating the love life of 17 year old Harriet Emma’s own life takes a turn toward maturity and growth. Emma’s initial goal was to make Harriet a better woman and decides that her current love interest Martin who is a farmer, will not factor into her plans for Harriet. To this end she introduces Harriet to Mr. Eton a Vicar whom she thinks is a better match for Harriet. Things go horribly wrong for Emma when Mr. Elton proposes to her instead and his conduct is not what Emma would have expected of him at all. This is just the start of Emma’s growth and maturity because as she learns more about people’s peculi arities she learns more about herself and in the process falls in love and learns a measure of humility as a result. The Adventures of Huckleberry Finn chronicles the adventures and growth Huck who is a young independent boy with both strength and stamina of character. Huck’s strength and character are tested early on when his father who is an alcoholic and violent returns to town and kidnaps him and holds him against his will. Huck’s independence and strength is demonstrated when manages to escape by faking his death following which he goes on the run with runaway slave Jim. My Name is

The Makings of a Hero Essay Example | Topics and Well Written Essays - 1250 words

The Makings of a Hero - Essay Example The Republic of the Philippines, an archipelagic nation located in Southeast Asia, classified among the third world countries, has made Overseas Contract Workers their most dynamic labor force, with more than 11 million workers abroad with remittances amounting to 64.7 billion pesos last year, it has played a major part in sustaining the economy of the country, making it the fourth (4th) largest recipient of foreign remittances behind India, China, and Mexico (source: en.wikipedia.org/wiki/OFW). But regardless of the economic help an Overseas Contract Worker can extend, the reality of being far away from home, living alone in a different land where traditions and culture vary from your own, letting others benefit from your talents and skills, serving and taking care for the needs of other's children while missing your own children's growing up years, is definitely, heartbreaking. But because of the will to provide a better quality of life, these OCW's carry on no matter the pain, with the hope that a better future is being stored for their loved ones with their hard work and perseverance. With all the struggles and sacrifices they are making, indeed, they are worthy to be the "Heroes of the Modern Day"- especially for countries where foreign notes have higher values than their own currencies, these Overseas Contract Workers, are really, doing a noble job. Anywhere in the world, a construction laborer can be found. Construction Workers, defined by Encarta as builders of large structures such as a house, road or bridge, can also be viewed as Heroes. These construction workers are usually people who were not able to acquire education, there were some who have entered school but more or less, not enough for a lighter, high-paying Mabini 3 job, thus construction become their only chance for toil. It is definitely not a career that one would choose if given the choice, but left without any option at all, they bear the work. Construction is definitely, not an easy employment. In fact it is one of the jobs considered to be most strenuous. It requires not just mental faculty with all those skills involved, not just stamina but superlative patience, but most of all, one has to have a strong and enduring physique to finish what has been started. With the construction workers around, people are assured that development will continue to flourish, roads will be constructed, buildings will keep on rising, bridges will be made to connect places and houses will be there for us to be our home- and all of these because there are people who are not afraid of taking all the risk in the workplace and are willing enough to

Spontaneous Recovery and Extinction Essay Example for Free

Spontaneous Recovery and Extinction Essay Spontaneous recovery from extinction is one of the most basic phenomena of Pavlovian conditioning. Although it can be studied by using a variety of designs, some procedures are better than others for identifying the involvement of underlying learning processes. A wide range of different learning mechanisms has been suggested as being engaged by extinction, most of which have implications for the nature of spontaneous recovery. However, despite the centrality of the notion of spontaneous recovery to the understanding of extinction, the empirical literature on its determinants is relatively sparse and quite mixed. Its very ubiquity suggests that spontaneous recovery has multiple sources. Previous SectionNext Section Experimental extinction is one of the fundamental observations of Pavlovian conditioning. Just as the arranging of a positive relation between a conditioned stimulus (CS) and an unconditioned stimulus (US) produces acquisition of conditioned responding, breaking that relation produces extinction of that responding. However, similar to many terms in the behavioral sciences, the word â€Å"extinction† is used in at least three different senses: as a procedure, as a result, and as an explanation. If we are to understand extinction experiments, it is extremely important that we keep these senses distinct from each other. One use of the term is as an experimental procedure or independent variable under the control of the experimenter, as when one says, â€Å"Following learning, we subjected the animal to an extinction procedure.† Most frequently, this is meant to refer to a procedure in which the original conditions of learning are disrupted. The most common extinction proce dure consists of presenting a stimulus alone, so that it now fails to signal the outcome. However, other procedures, such as retaining the US but arranging for it to be independent of the CS are also available and of interest (see Rescorla 2001a). Another use of the term is as an experimental result or dependent variable under the control of the animal, as when one says, â€Å"When the stimulus was presented alone, the behavior extinguished.† The prototypical example is one in which responding that was established by training deteriorates, often to a level such as that prior to learning. A third use of the term extinction is as a process or  intervening variable that is intended to provide an explanation, as when one says, â€Å"When we arranged for the stimulus to be presented alone, the behavior deteriorated because of extinction.† Normally, it is this process that is of interest. We would like to understand the basis of the change in behavior resulting from the change in procedure, whether that understanding is achieved at a conceptual or a neural level . Consequently, throughout this article the term extinction will refer to the learning process inferred when the procedure produces a particular result. When there is the possibility of misunderstanding, the phrase â€Å"extinction process† will be used. Because interest primarily centers on the learning process that occurs as a result of an extinction procedure, it is important to separate that learning from a wide variety of other effects that govern performance. The issue here is analogous to that of understanding the learning that occurs during an acquisition procedure. Elsewhere we have argued that the measurement of learning demands attention to two points in time: t1, during which the opportunity to learn is given, and then a separate t2, during which an assessment is made of that learning (see Rescorla and Holland 1976; Rescorla 1988). The comparison that indicates that learning has occurred is that between two animals (or two stimuli or responses) given a common t2 test following different opportunities for learning at t1. This comparison is superior to the common alternative of examining responding during t1, at which the animals are receiving different learning treatments. Data taken during t1 necessarily confound the differences in the current circumstances under which learning is assessed with differences in the learning that prior treatments might have produced. We have argued that for this reason acquisition curves are in fact deeply flawed as a way to measure learning. A similar point applies to the learning that occurs in extinction. In this case, we need to administer a common test for stimuli or animals given different extinction experiences, as indicated in the first portion of Figure 1. In the simplest case, we can compare responding to two stimuli (S1 and S2) at a common t2 after both have had the same initial acquisition but then differ in whether or not they were given extinction at t1. Differences in t2 test performance would then index the differences in learning that occurred at t1. Clearly, comparisons between stimuli during the t1 extinction experience are of limited value because any differences might be  the product of the current conditions of testing rather than of the memory for the learning that has occurred. That is, extinction curves are of very limited use in understanding the underlying process. Figure 1 View larger version: In this page In a new window Download as PowerPoint Slide Figure 1 Experimental designs for the study of extinction and spontaneous recovery. (A) A recommended procedure for studying extinction, in which the critical comparison is responding to S1 and S2 at a common test time when the two stimuli differ in their extinction history. (B) The design in which spontaneous recovery is sometimes inferred from the greater responding to S1 during test than during extinction. (C) A better spontaneous recovery design in which S1 and S2 are both trained and extinction, but then tested for recovery after different time periods. (D) An alternative design in which S1 and S2 are tested in a common test session, despite different times between extinction and test. In this context, the phenomenon of spontaneous recovery has a complex role. That phenomenon suggests that the results that we obtain in a t2 assessment may be quite different depending on the length of time that intervenes between the t1 extinction experience and the t2 test. It has been known since Pavlovs (1927) early experiments that the loss of behavior that results from presenting the stimulus alone at t1 is not entirely permanent. Rather, with the passage of time following nonreinforcement, there is some â€Å"spontaneous recovery† of the initially learned behavior. Introducing greater time delays between t1 extinction treatment and t2 test provides the opportunity for greater spontaneous recovery. At minimum, the phenomenon of spontaneous recovery provides some information about what process fails to account for the loss of behavior when an extinction procedure is conducted. It suggests that the loss does not simply involve the removal of what was learned in acquisition. As Pavlov noted, if an extinction procedure had erased the acquisition learning, then there would be no basis for behavior to return with time. It suggests that instead something happens during the extinction procedure that temporarily  suppresses performance while leaving some of the initial learning in place. Of course, the finding of spontaneous recovery does not imply that there is no removal of the initial learning or even that there was any learning during extinction. It only implies that some of the initial learning survives an extinction procedure. The finding of spontaneous recovery may also be taken as providing some information on the nature of the processes that suppress behavior. If one believes, as Pavlov did, that the return of behavior after nonreinforcement represents the loss of a learning process that occurred during the extinction procedure, it suggests that this learning is malleable, changing with time. That is, it suggests that one property of the extinction mechanism is its relatively lower stability with time. For both of these reasons, many have hoped to learn something about the processes underlying performance loss in extinction by an investigation of spontaneous recovery. Although there have been substantial advances in the neurobiological study of extinction in the last few years (for reviews, see Myers and Davis 2002; Delamater 2004), almost all studies of spontaneous recovery have been at the purely behavioral level. Consequently, the discussion that follows will focus exclusively on such behavioral studies. Previous SectionNext Section Designs for Studying Spontaneous RecoveryThe standard description of spontaneous recovery is that the responding that was depressed during an extinction session is partially restored in a test session that is administered after a delay. As illustrated at the second panel of Figure 1, spontaneous recovery is commonly inferred from a comparison between responding at the end of an extinction session and at the beginning of a test. Greater response in the test is taken to mean that some portion of the initial learning survived the extinction. Implicit in this interpretation is the assumption (1) that the behavior that appears on the early trials of the test session is attributable to the original learning rather than to something else, and (2) that the increase between the extinction and the test represents a reduction in the effect of the learning that occurred in extinction. To justify the first assumption, comparison really should be made between responding to an extinguished stimulus and responding to one that has never been trained prior to extinction but is still given the same  interval between extinction and test sessions in which to â€Å"recover.† Otherwise, it is possible that the increase in responding represents a general tendency to increase responding with time independently of the original acquisition; that is, it might not reflect recovery of the initial learning at all. In fact, there are only a few studies (see Robbins 1990) that have deliberately made such a comparison. But any detailed investigation of spontaneous recovery should be sensitive to this possibility. To justify the second assumption (that the increase in responding represents dissipation of the extinction learning), comparison should be made with a stimulus that has trained, but not been extinguished, and that evokes responding at a level comparable to that of the extinguished stimulus before the delay interval. For instance, one might compare, for the same animal, changes with time in a trained and extinguished stimulus and a stimulus that is only partially trained, so as to attain the same response level. It is only if the former stimulus shows greate r growth with time that one would conclude that there is a loss of the learning that occurred during extinction, as distinct from a general change in performance for any previously trained stimulus showing behavior at that level. Aside from the need to occasionally include these comparisons, the spontaneous recovery design shown in Figure 1B has the drawback of repeated testing with the same stimulus, with the consequence that different numbers of extinction trials have necessarily preceded the trials being compared. A better design, which is also frequently used, is shown in Figure 1C. In that design two stimuli are both trained and extinguished but then given different amounts of time to recovery prior to the test. This design avoids repeated testing on the same stimulus and has the advantage of an explicit test session. But unfortunately, the tests of the two stimuli differ not only in the time since extinction but also in the time since original training and in the overall test context and age of the animal. To avoid these confoundings, we have frequently adopted a somewhat different design for studying spontaneous recovery, as illustrated in Figure 1D. In this comparison, two groups of animals receive co nditioning followed by extinction and a test. The groups differ in the placement of the extinction with regard to the test. For one group (S1) the extinction occurs at a temporal distance from the test, so as to allow spontaneous recovery. For the other group (S2), extinction occurs  immediately prior to test, minimizing recovery. The evidence for recovery is then the difference in responding at the time of the common test. That allows comparison of responding during the same test session, after the same number of extinction trials, to stimuli that share the time since original training but differ in the time since their extinction. The design can be further strengthened if the two stimuli are both trained in the same animal. An especially important advantage of such a within-subject comparison between S1 and S2 is that it involves a common test session in the same animal. This means that any recovery cannot be attributed to general changes in the animals state or to differential similarity of the test conditions to those of original training. One difficulty with the standard procedure for assessing spontaneous recovery is that one part of the comparison comes from a session in which the animal is undergoing an extin ction procedure and is therefore likely to be experiencing a variety of new stimulus events that may have various emotional consequences. The presence of those new events could, in themselves, artificially depress responding to a lower level than that which is warranted by the learning that is occurring. The likely absence of those stimuli at the beginning of the test session could allow greater responding for reasons that are not central to the learning that is occurring in extinction. But the final design avoids such differences in the context of performance for the stimuli being compared. By using within-subject versions of this last procedure, Rescorla (1997a,b) has shown evidence of substantial spontaneous recovery in a variety of conditioning preparations. An example is shown in Figure 2 for a Pavlovian magazine approach situation with rats. In this preparation, S1 and S2 are counterbalanced as a 30-sec light and noise, each paired with the delivery of food and then given nonreinforcement. The result is an increase and decrease in anticipatory responding involving investigation of the food delivery site, the maga zine. A test then takes place either immediately after the last extinction session or after a delay. The comparison of interest is that between S1 and S2 in the common test session. Figure 2 clearly indicates greater recovery for the stimulus extinguished first, S1. One may note that S1 also shows more responding in the test than it did at the end of extinction; but as noted above, this comparison is flawed. Figure 2 View larger version: In this page In a new window Download as PowerPoint Slide Figure 2 An illustration of spontaneous recovery using the design shown in Figure 1D. Rat subjects were given Pavlovian magazine-approach training and extinction with two stimuli, S1 and S2, and then tested in a common session. The superior responding in S1, compared with S2, is used to infer spontaneous recovery. Of course, no procedure is without its shortcomings. In this alternative procedure for assessing spontaneous recovery, one of the stimuli must necessarily be extinguished before the other. Consequently, the order in which the stimuli are extinguished, and the interval between training and test, are both confounded with the interval of interest, between extinction and test. Although application of the design has not revealed any resulting differences in the course of extinction itself (Fig. 2), one must still be cautious about the implications of such a confounding. Consequently, it may be most wise to use both procedures C and D in any research program investigating spontaneous reco very. Previous SectionNext Section Bases for Spontaneous RecoverySpontaneous recovery is such a widespread phenomenon, both in terms of the variety of learning paradigms in which it occurs and the frequency with which it is reported, that it would be surprising if it had only one source. Indeed, many different sources have been suggested, most of which have received some empirical support. But not all of these are of equal interest in helping us understand the learning involved in extinction. Here, I attempt a rough categorization of those sources. Local Performance EffectsAs noted above, when one makes the standard comparison of responding on the final trials from extinction with that on the initial trials in a test session, one can expect that they will differ in a number of ways unrelated to the learning that occurs in extinction. For instance, the repeated evocation of a conditioned response might lead to temporary fatigue that adds to the loss of behavior. It is not uncommon to see behavior decline over the course of a conditioning session  even when reinforcement continues (see McSweeney and Swindell 1999). Similarly, the surprising deletion of anticipated reinforcement may well lead to emotional responses that have a disruptive effect on performance. For instance, the surprising omission of food can be expected to lead to frustration, which changes the stimulus environment and may evoke responses of its own (see Amsel 1958). Effects such as these might well be expected to dissipate before the beginning of the test session, hence revealing any incompleteness of the extinction process that they masked at the end of the extinction session. Although such effects may contribute to the deterioration of performance during the administration of an extinction procedure, they may have little to do with any underlying learning process. If spontaneous recovery could be accounted for solely on the basis of such effects, it would be of substanti ally less interest. Contributors of this sort to response suppression seem especially likely to affect the standard spontaneous recovery designs that compare responding to the same stimulus in two different sessions. They are less likely to contribute to recovery when it is measured as the difference in responding to two stimuli during the same test session. Indeed, part of the motivation for developing the alternative assessment of spontaneous recovery (D) was to reduce the various general differences that are confounded when responding in two different sessions is compared. Spontaneous Recovery Despite Loss of Acquisition LearningDespite the widespread agreement that spontaneous recovery indicates that the primary extinction process does not involve the erasure of the original learning, there have been some attempts to preserve an erasure theory and still explain recovery. Perhaps the most well known attempt is the suggestion by Skinner (1938) that an extended extinction session leaves the stimuli fro m the beginning of the session incompletely extinguished. Consequently, those stimuli still have some strength that can be exhibited at the beginning of the next session. Skinner seems to have believed that extinction eventually removes all of the original learning but initially leaves the session-beginning stimuli partially effective, thereby explaining spontaneous recovery. Although there is some evidence that stimuli that are explicitly presented by the experimenter at the start of a session can retain some strength when extinction takes place in their absence (see Burstein and Moeser 1971), it seems unlikely that this will fully account  for spontaneous recovery. Several experiments have found evidence of strong spontaneous recovery even when the session starting stimuli are well controlled (see Thomas and Sherman 1986) or when an extinguished stimulus is tested in the middle of a session only after another stimulus has completely lost its spontaneous recovery (see Robbins 1990). Moreover, it is hard to see why this account would anti cipate one of the basic findings of spontaneous recovery, that it increases with the passage of time. A somewhat more successful version of such an account was offered by Estes (1955) as a component of his influential stimulus sampling theory. Estes argued that what experimenters identify as stimuli can actually be viewed as constructed of many elements with occurrence that fluctuates in time. Acquisition and extinction produce changes in the associations between the outcomes and those elements over the course of trials. According to that theory, when an element is paired with a reinforcer, it immediately becomes fully conditioned; when it is presented without reinforcement, it immediately reverts to its unconditioned state. It is only the random fluctuation in the selection of elements over trials that gives the normally observed gradualness to changes in behavior. At heart, this is a theory in which extinction involves the actual erasure of learning. The important point to notice is that when trials are given in close proximity, they tend to share more elements; when trials are separated, then they sample different elements from the pool that constitutes a given stimulus. Consequently, with repeated extinction trials, performance can decrease even though some unsampled elements remain conditioned. With the passage of time, the likelihood of sampling those nonextinguished elements can increase, generating spontaneous recovery. Like the account offered by Skinner, this account correctly predicts that repeated extinction will diminish spontaneous recovery. Unlike that account, it gives no special role to session-initiating stimuli, and it can account for the growth in recovery with time. The stimulus sampling theory also correctly anticipates the occurrence of spontaneous recovery with all of the various assessment procedures. These successes demonstrate that one can account for at least some of the basic facts about spontaneous recovery even on the assumption that the extinction process involves (partial) removal of the original learning. They also highlight the fact that the observation of spontaneous  recovery does not imply that extinction must leave all of original acquisition in place. Spontaneous Recovery as an Indication That Extinction Involves Inhibition If one envisions an extinction procedure as leaving intact even a portion of the original learning, then it is natural to conclude that some new learning is occurring that is superimposed on acquisition and prevents performance. The classic candidate for such new learning has been â€Å"inhibition.† A wide variety of different kinds of inhibition have been proposed, suggesting quite different ideas about the nature of extinction. But in each case, spontaneous recovery is accounted for by the dissipation of that inhibition with the passag e of time. CS-Based InhibitionPavlov (1927) was the first to suggest that extinction involves inhibition and that spontaneous recovery is an indication that this was so. He viewed the learned inhibition that he supposed to occur during extinction as more vulnerable than the excitation that develops in acquisition to such intrusions as the presentation of a new stimulus (i.e., disinhibition) and the passage of time (i.e., spontaneous recovery). Although it is not widely appreciated, Pavlovs notion of inhibition was highly focused on the CS and was envisioned to develop independently of whether or not the reinforcer occurred. Pavlov believed that every CS presentation leads to the building up of a kind of fatigue in the neural cells stimulated by that CS, whether or not the reinforcer followed. This leads to a reduced ability of the CS to stimulate its neural targets, which would in turn lead to reduced behavior. That is, the natural consequence of repeatedly presenting the CS is a deterioration of behavior. However, during acquisition, this process is overwhelmed by the growth of an association which the CS develops with the reinforcer. With rest, the CS-based inhibition fades and responding can recover. Robbins (1990) proposed a related notion of inhibition, which he described in terms of reduced attention to the CS. He suggested that during acquisition, attention to the CS grows whereas during extinction it falls. Part of the reason for the decline of behavior in extinction is then reduced attention to the CS with the attendant loss in its ability to evoke responding. With rest, that attention partially returns. Unlike Pavlov, Robbins envisioned the effectiveness of the CS as dependent on the trial consequence, growing with reinforcement and declining with nonreinforcement. In support of this view,  Robbins (1990) found evidence, in a sign-tracking preparation with pigeons, that a CS los t its ability to serve a variety of different functions during an extinction procedure but then recovered them with time. He trained a CS simultaneously to have an excitatory association with a US and also to serve as a conditional signal that another CS would not be followed by a US. When he extinguished the excitatory association, the CS lost both properties and then regained them both with the passage of time. That result is consistent with the view that one contributor to the loss of behavior with extinction and its restoration with time may be changes in the processing of the CS per se. On the other hand, both Bouton and Peck (1992) and Rescorla (1997a) have found evidence for spontaneous recovery following counter-conditioning in which one US is replaced with another. Because counter-conditioning yields a CS that continues to produce some behavior, those cases of spontaneous recovery seem unlikely to be attributable to loss and recovery of the processing of the CS. Of course, the processes underlying spontaneous recovery after such procedures may differ from those underlying the changes after extinction. Response-Based InhibitionShortly after Pavlovs work became available in this country, Hull (1943) suggested a similar account of extinction and spontaneous recovery that focused on the response rather than on the stimulus. As part of a multiprocess account of extinction, Hull argued that each occurrence of a response leads to the building up of a fatigue-like process that is specific to that response and that reduces its subsequent likelihood of occurrence. This process contributes to the decrease in performance during extinction but dissipates with time, permitting spontaneous recovery. Similar to Pavlov, Hull seems to have believed that the changes in this response-fatigue are independent of reinforcement contingencies; indeed, he believed it left no permanent learning impact at all. That is, this particular inhibitory notion is more akin to the performance effects discussed above. It has proven difficult to confirm the most obvious implication of such an approach, that the effortfulness of the response should influence the course of extinction and spontaneous recovery (see Mackintosh 1974). But, one advantage that can be claimed for the alternative test of spontaneous recovery described above is tha t it provides a common test session in which all stimuli should share any general fatigue processes. Outcome-Based InhibitionOne way of viewing  extinction is that a CS that was once followed by an effective outcome is now followed by an ineffective one. Indeed, there is evidence that if the outcome potency is deliberately partially reduced, then behavior partially deteriorates (see Wagner and Rescorla 1972; Kehoe and White 2002). This suggests the possibility that one change that occurs in extinction involves a reduction in the memory of the outcome itself. Based on this kind of thinking, Rescorla and his collaborators (see Rescorla and Heth 1975; Rescorla and Cunningham 1978) suggested that one process that occurs in an extinction procedure is a depression in what they called the â€Å"US representation.† This led them to explore manipulations that might affect the state of the US representation independently of its association with a particular CS. By using a fear conditioning preparation in rats, they documented the phenomenon of â€Å"reinstatement† first report ed by Pavlov, that responding could be restored to an extinguished CS by separate presentations of the US alone. Although others (see Bouton 1984) have given different accounts, Rescorla and Cunningham described this manipulation as restoring a portion of the extinction-depressed US representation. They also argued that there might be a recovery in the US representation with time, leading to the phenomenon of spontaneous recovery of responding to the CS. In support of that possibility they found that, under some circumstances, recovery could be undermined by the nonreinforcement of another CS immediately prior to testing, a manipulation presumed to reduce the US representation. However, various other implications of this notion have not received support. For instance, Robbins (1990) found evidence of independence in spontaneous recovery for two stimuli that had been conditioned with the same US. Moreover, Tomie et al. (1980) reported spontaneous recovery after an extinction procedure in which the US was continued but made independent of the CS, a procedure that should maintain the US representa tion. Nevertheless, it is possible that changes in the memory for the US may make a contribution to spontaneous recovery in some preparations. Associative InhibitionMost contemporary views of Pavlovian inhibition involve not individual events but rather associations between events. For instance, Konorski (1948) argued that a variety of conditioning paradigms, including extinction, lead to the development of an inhibitory association between the CS and US that is parallel to, but the opposite of, the excitatory  associations set up during acquisition. In later writings, Konorski (1967) offered a somewhat different account, according to which inhibitory learning involves associations between the CS and a consequence that is the opposite of the US, the â€Å"no US.† Most contemporary discussions of Pavlovian inhibition implicitly accept one or the other of these views. The standard ways of detecting such associative inhibition are to ask whether an inhibitory stimulus can reduce responding to an otherwise effective excitor (a summation test) or is slow to acquire excitation if it now receives an excitatory training treatment (a retardation test; Rescorla 1969). Most contemporary evidence suggests that an extinguished stimulus does not in fact demonstrate net inhibition with either of these tests. Presumably this is because the inhibition that builds up during nonreinforcement is only just sufficient to counteract the original excitation, but does not develop beyond that level so as to generate a net inhibitory stimulus. However, there is some evidence that an originally neutral stimulus that accompanies an excitatory CS during an extinction procedure does capture inhibition, as assessed by these tests (see Rescorla 1979, 1999). Moreover, there a re some reports (see Henderson 1978) that a net inhibitory stimulus does lose some of its inhibitory properties with the passage of time, in the way required if this were to contribute to spontaneous recovery. An alternative associative basis for extinction has been proposed by Colwill (1991) and explored by Rescorla (1993). According to that account, the inhibition that develops during extinction involves associations between the stimulus and a response. These inhibitory S-R associations are envisioned as existing side by side with excitatory associations that involve the US. Consistent with this view (but not with the notion of inhibition between the CS and US), Rescorla (2001b) used outcome-specific transfer procedures to reveal that the CS-US associations maintained their full net strength after extinction, despite the reduction in responding. Moreover, he found no evidence that those CS-US associations changed in the way expected with the passage of time if they were to be the basis of spontaneous recovery. He proposed instead that extinction can involve an associative response-specific process that depresses responding but deteriorates with time. An alternative view of Pavlovian conditioned inhibition in terms of modulation has received substantial recent attention. Several investigators (see Holland 1983,  Rescorla 1985) have suggested that under some circumstances an inhibitory stimulus does not develop an association with a separate event, such as US or a response, but rather acquires the ability to control the strength of an excitatory CS-US association. This type of inhibition is not the opposite of an excitatory association but rather plays more of a hierarchical role, modulating a CS-US association. Bouton (1991) has suggested that both contextual and temporal stimuli can serve this modulatory role for a stimulus subjected to an extinction procedure. During the extinction procedure, the excitatory association is seen as remaining intact but being disabled by the presence of contextual or temporal stimuli that had accompanied nonreinforcement. With a change in either the context or the temporal stimuli, this inhibitory process is attenuated, allowing the return of performance. The phenomenon of â€Å"renewal† provides evidence for this view. If, following extinction, the stimulus is tested in a different context, there can be a substantial recovery of responding (see Bouton 1991). If one views the passage of time as analogous to changing the context, this view provides a way of conceptualizing spontaneous recovery. Differential RetrievalThe inhibitory accounts of extinction and spontaneous recovery all envision the strength of original learning as remaining unchanged throughout extinction and spontaneous recovery. They see the decrease in responding during extinction as attributable to the growth of the inhibitory process, and the increase in responding with spontaneous recovery as attributable to the dissipation of that inhibitory process. In effect, the memory for the extinction process loses strength with the pas sage of time. An alternative framework for understanding extinction and spontaneous recovery involves differential retrieval of the acquisition and extinction experiences, both of which remain fully intact. For instance, Spear (1971) and Bouton (1993) have both noted the formal analogy between interference paradigms as studied in humans and the acquisition/extinction sequence of Pavlovian conditioning. In both cases, the organism is exposed to two competing pieces of information that might be expected to interfere with each other. This led both investigators to the proposal that differential performance might reflect differential likelihood of retrieving the two experiences, rather than a weakening of stored information about either experience. According to this view, manipulations that make the  retrieval of one experience or the other more likely will result in changes in overall performance. For instance, a stimulus that accompanies extinction might serve as a retrieval cue, presentation of which would promote the retrieval of the memory for extinction. Evidence for such a process can be found in the ability of some such stimuli to diminish the magnitude of spontaneous recovery (se e Brooks and Bouton 1993). A related view, focusing specifically on spontaneous recovery, is incorporated in Devenports (1998) temporal weighting rule. According to that rule, when an animal has multiple experiences with a stimulus prior to a test, it weights those experiences according to the relative time that has passed between each and the test. In the case of acquisition followed by extinction, this means that performance will deteriorate under the currently experienced nonreinforced treatment. However, as time passes, the relative temporal advantage enjoyed by the recent nonreinforcement experience will diminish, leading to spontaneous recovery. On views such as these, there is a permanence for both the acquisition and extinction experiences; what changes with time is their relative likelihood of retrieval. As this discussion indicates, a broad range of different processes have been envisioned as contributing to the decrement in performance resulting from an extinction procedure and to the recovery from that decrement with the passage of time. Moreover, one can identify evidence supporting each idea. It seems likely that each of these may contribute to the changes in various situations. However, none of them seems sufficient to provide an account on its own. One challenge that each contributor faces is to provide an account of the demonstrated empirical determinants of spontaneous recovery. For this reason it is worth reviewing some of those determinants. Previous SectionNext Section Basic Empirical PropertiesDespite the centrality of spontaneous recovery to the phenomenon of extinction, there is actually surprisingly little well-documented information on its detailed properties. However, four features of spontaneous recovery seem to be widely accepted. Spontaneous Recovery Increases in a Negatively Accelerated Fashion Over Time Almost every description of spontaneous recovery includes the claim that recovery is greater the greater the delay between extinction and test. Indeed, there is a sense in which greater recovery with more time is a defining property.  Moreover, the form of that increase appears to be negatively accelerated. For instance, in recent years, negatively accelerated recovery has been found with eyelid conditioning in rabbits (Haberlandt et al.1978), sign-tracking in pigeons (Robbins 1990), and fear-conditioning in rats (Quirk 2002). Almost all of the potential contributors to recovery listed above appear to be consistent with such a pattern o f change. Although the various inhibitory theories make no specific predictions about how that inhibition fades with time, the negatively accelerated nature of many biological processes makes the finding unsurprising. The stimulus sampling mechanism described by Estes (1955) and the differential weighting rule proposed by Devenport (1998) also yield this expectation. Perhaps the only potential contributor that does not anticipate this is Skinners (1938) suggestion that at the beginning of the session stimuli retain their ability to evoke a response. Spontaneous Recovery Is IncompleteAlthough Pavlov claimed to have observed full recovery from extinction, most other investigators have reported only partial recovery. Even when recovery of responding appears to be complete on the first test trial, the rapid loss of responding over the course of testing suggests that recovery was actually less than full (notice, for instance, the rapid loss during testing shown in Fig. 2). The incompleteness of recovery appears to be mandated by some of the mechanisms described above. For instance, the stimulus sampling account of Estes and the weighting rule of Devenport appear incapable of allowing the impact of extinction to disappear altogether. The other mechanisms are less well-specified in this regard. Spontaneous Recovery Declines With Repeated ExtinctionIt is widely agreed that the greater the amount of extinction, the less the magnitude of spontaneous recovery after any fixed waiting time. This most frequently shows up as the reduced amount of recovery from day to day over multiple days of extinction. An illustration of that decline is shown in Figure 3, which displays results from a recent magazine-approach study with rat subjects done in our laboratory. That figure shows responding during repeated daily extinction sessions in which a 30-sec noise was presented eight times without its food pellet. Another stimulus, a light, received intervening reinforced trials. It is clear that there is repeated recovery of responding that gets smaller over the course of extinction. Figure 3 View larger version: In this page In a new window Download as PowerPoint Slide Figure 3 The decline in the magnitude of spontaneous recovery with repeated extinction. Rat subjects were given Pavlovian magazine-approach training with a noise and then repeated extinction sessions. Actually, in the absence of some better understanding of scaling issues, it is difficult to compare quantitatively the amounts of recovery for stimuli that have undergone different amounts of extinction. Clearly, if minimal extinction has occurred, there is less decrease in behavior and hence less opportunity for recovery to occur. Similarly, with massive extinction, performance may be at a floor, and hence, even substantial recovery may be difficult to detect. But most mechanisms of recovery appear to anticipate that the deeper the extinction the less the recovery. That prediction is obligatory for accounts of recovery such as that offered by Estes and by Devenport, who see repeated extinction as accumulating a relatively permanent depressive process. Data such as those shown in Figure 3 are commonly taken as consistent with this prediction. Spontaneous Recovery Can Be Brought Under Stimulus ControlThere is good evidence that the learning process that occurs during extinction can be brought under stimulus control. For instance, Rescorla (1979) reported that a stimulus present during the nonreinforcement of a previously trained excitor took on the properties of a conditioned inhibitor, suppressing responding to other excitors. Indeed, the so-called conditioned inhibition paradigm consists of little more than intermixing reinforced and nonreinforced presentations of a stimulus while signaling the nonreinforced presentations by a second stimulus. Similarly, Bouton (1991) has reported that if the context present during extinction is removed by testing in another context, then the suppressive effects of extinction are reduced and behavior is â€Å"renewed.† Brooks and Bouton (1993) have extended these observations to the responding observed in spontaneous recovery. They found (see also, Brooks 2000) that if an explicit stimulus is present during extinction of an excitor, then that stimulus has the ability to diminish  spontaneous recovery if it is presented at the time of the test. Although few theories of extinction are challenged by the observation that whatever is occurring in extinction can be brought under the control of a stimulus, retrieval theories seem like the most natural account. For instance, Bouton has argued that a stimulus present during extinction is especially good at retrieving a memory for a CS-US association. There is now substantial evidence that one stimulus can be learned as a signal of the relation between another stimulus and the US (see Schmajuk and Holland 1998). Such modulation or â€Å"occasion setting† could be the mechanism by which explicit stimuli, contexts, or even time, might activate the mem ory of a CS-US association (see Bouton 1991, 1993). Previous SectionNext Section Determinants Needing Further InvestigationIn addition to these four well-established findings, there are a variety of other manipulations that have been claimed to affect spontaneous recovery but for which there is substantially less or even contradictory evidence. This is unfortunate because the effects of many of these manipulations might be informative in identifying the contributions of particular mechanisms of recovery. The Symmetry of Spontaneous Recovery and RegressionAccounts of spontaneous recovery differ in the degree to which they treat extinction as engaging a special learning process with distinctive properties, such as the likelihood of its memory fading in time. Beginning with Pavlovs, the various proposals of inhibitory processes have tended to see them as different from excitatory process precisely in their greater instability with the passage of time. This is clearly true for the fatigue-like processes mentioned by Pavlov, Robbins, and Hull, but it also seems true o f some associative inhibition accounts, such as those described by Rescorla and Bouton. By contrast, the stimulus sampling theory of Estes and accounts that appeal to retrieval or relative weighting seem to make little distinction between acquisition and extinction processes in their inherent vulnerability to time. They see the animal as integrating two experiences that it receives sequentially in time in a similar way regardless of the identity of those processes. This means that the latter accounts anticipate that one should observe a companion phenomenon to spontaneous recovery from extinction if one were to interchange the order in which extinction and acquisition were administered.  That is, they expect to see regression of responding after acquisition if that acquisition were preceded by some sort of nonrein-forced training. The evidence for such regression is highly mixed. Notice that the simple deterioration of performance from day to day during acquisition is not sufficient to identify regression that is the opposite of spontaneous recovery. The critical obse rvation is that there is a deterioration in performance that is attributable to a prior history of nonreinforcement, just as the critical observation for spontaneous recovery is that there is an improvement with time that is specific to stimuli that have a history of reinforcement. When animals are given in sequence two reinforcement experiences that differ in reinforcer valence or frequency, there is evidence that regression in the direction of the first performance can be observed with time (see Bouton and Peck 1992; Mazur 1996). But the results are less clear when nonreinforcement of a stimulus precedes reinforcement prior to the waiting period. Some early experiments reported positive results (see Spear et al. 1965; Konorski 1967). But some more recent studies have found no evidence for regression or the opposite results (see Kraemer et al. 1991; Rescorla 2001b). Clearly it would be valuable to understand the circumstances under which one obtains either regression or its opposite if one is to evaluate the contributions of various mechanisms to spontaneous recovery. It will surely be important to distinguish among different kinds of nonreinforcement experience that might precede reinforcement. The simple exposure to a stimulus prior to any reinforcement is certain to endow it with properties different from those of a stimulus that signals nonreinforcement explicitly, as in the case of conditioned inhibition training or even extinction. But there are not sufficient data to indicate whether or not this distinction matters for the production of regression. Recovery Following Massed or Spaced Extinction TrialsThere is reason to anticipate that conducting extinction with short intertrial intervals may encourage more rapid response decrement followed by more substantial recovery. Certainly this is the expectation of accounts such as that of Hull, which emphasizes short-term fatigue-like effects, and of Estes, which emphasizes that massing of trials would yield repeated sampling of the same stimulus elements but neglect of others. Indeed, one might argue that there is a logical sense in which spaced trials should lead to slower decrement  and less recovery. Presumably widely spaced trials would allow for any recovery between individual trials, resulting in slower behavioral loss over the course of an extinction procedure but more substantial change by the time that a test for recovery is imposed. Despite the appeal of these arguments, the evidence on the impact of massing or spacing extinction trials is quite mixed. A number of investigators (see Rescorla and Durlach 1987; Cain et al. 2003) have reported that massing produces rapid loss of performance. However, Rescorla and Durlach reported no difference in the magnitude of responding in a subsequent test for spontaneous recovery and Cain et al. (2003) reported continued less responding after massed extinction even with the passage of time. To complicate matters further, Stanley (1952) reported that for an instrumental training task, massing slowed extinction on one measure and speeded it on another in an instrumental choice situation. Interval Between Learning and ExtinctionAlthough most attention has focused on the interval between extinction and the recovery test, it is also of interest to ask about the impact of the interval between the original training and extinction, as a determinant of spontaneous recovery. The retrieval theory proposed by Spear and the weighting rule described by Devenport both suggest that spontaneous recovery should be maximal when the interval between acquisition and extinction is minimized. In both cases, the intuition is that when training and extinction are close in time, it should be more difficult for the animal to recall which is the more recent. Immediately after extinction, the relative temporal recency of the nonreinforced experience should be maximal. However, as time passes, and the two experiences are more equally distant in time, they should become more equivalent in their likelihood of being retrieved. The increase in the relative likelihood of retrieving the original acquisition experience would then produce spontaneous recovery. A similar reasoning would lead to the relatively greater impact of the acquisition experience according to the weighting rule. Mechanisms of recovery that appeal to the loss of the extinction experience have no natural way to predict that the interval between training and extinction should matter. Unfortunately, there are very few attempts to examine this possibility. There is some supportive evidence from studies of proactive inhibition in humans (Underwood and Freund 1968) and from  counter-conditioning in rats (Gordon and Spear 1973), but little for the case of extinction. Recently, Rescorla (2004) has reported that a longer time interval between training and test diminishes spontaneous recovery in magazine approach and instrumental responding in rats and in sign-tracking in pigeons. One illustration is shown in Figure 4. That figure displays the results of extinction and testing with two stimuli given acquisition, extinction, and a test for spontaneous recovery in a magazine-approach procedure using rat subjects. The stimuli shared the same 48-h recovery interval after extinction but differed in that a greater interval (8 d versus 1 d) intervened between training and extinction for S1 than for S2. The two stimuli showed virtually identical behavior over the course of extinction. However, the results of a test for spontaneous recovery given 48 h after extinction show greater spontaneous recovery for the stimulus with the shorter training/extinction interval (S2). Figure 4 View larger version: In this page In a new window Download as PowerPoint Slide Figure 4 Evidence for greater spontaneous recovery with a greater interval between training and extinction. Rat subjects were given Pavlovian magazine-approach training, extinction, and a common test for spontaneous recovery with two stimuli, S1 and S2. The stimuli differed in the interval between their original training and extinction. Results such as these suggest that, consistent with some retrieval theories, spontaneous recovery may be a decreasing function of the acquisition/extinction interval. But clearly more work needs to be done on this potentially informative parameter. Previous SectionNext Section Conclusion The picture that emerges from this discussion of spontaneous recovery is one of a process that is greatly in need of further empirical investigation. The available evidence fails to identify any one proposed process as the sole basis for spontaneous recovery. However, there is also evidence in support of all of the suggestions so far offered. This, together  with the ubiquity of spontaneous recovery, encourages the belief that it is a result that is multiply determined. Perhaps this is not surprising because it seems almost certain that the response decrement that is observed in extinction itself has multiple contributors. The fact that spontaneous recovery is likely to have multiple sources limits our ability to use it to identify the learning underlying extinction. The inference that extinction does not fully remove all of original acquisition seems secure. Spontaneous recovery is joined by a variety of other phenomena, such as disinhibition, renewal, reinstatement, and augmented summation (see Reberg 1972) as a basis for that inference. But the simple observation of spontaneous recovery does not force the inference that all of original learning remains nor even that the learning that occurred during extinction fades in time. In the light of this conclusion, it is unfortunate that we do not have a clearer picture of how some of the parameters of most potential interest affect spontaneous recovery. But it suggests that if one is to use spontaneous recovery as a tool to understand the nature of the processes occurring in extinction, one cannot simply celebrate its occurrence or its failure to occur. We will have to do much more analytic experiments determining the circumstances under which it occurs in the particular extinction situation under study.