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Short-Term Memory

5 Pages

Course Code
Psychology 2135A/B
Robert Brown

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Lecture 7 - Short Term Memory The case of Clive Wearing - random convulsions, except in music; can still play piano (different kind of memory that has been preserved) - could still remember to play music and sing, but no longer able to remember things for over 20- 30 seconds - very little memory before and after illness - experiences things are like just waking up - declarative memory (things able to talk about); procedural memory (things know how to do, usually survives) - recognizes wife but not children; like seeing her for the first time in a long time - some manners have survived - what life would be like if all we had was STM - lost some semantic memory, even those prior to injury; cannot learn new semantic memory - brain scans show some loss of fluid and other parts William James on memory - see quote on WebCT Donald Hebb on memory - 1949, the Cell Assembly model - neurons that fire together wire together - every time neuron A sends a signal to neuron B as part of response to a stimulus, connection between two becomes stronger - stronger connection means stronger signal from A arriving at B, so it is more likely that B will fire as a result; more likely that both fire together - two ways to represent experience: - which neurons are active right now in response to what just happened - state (what goes on right now) - strengths of connections between neurons, which reflect experience (learning) - trait (structural changes over a period of time due to experience) - strengths of connections = LTM - LTM is structural changes in the nervous system - active right now = STM - STM = changes in activation level George Miller (1956) on short-term memory - the magical number seven, plus or minus two - capacity of STM - consistent finding of a limit on human ability to remember information - but amount of information in immediate memory can be increased through chunking - chunk is a collection of elements strongly associated with one another but weakly associated with elements in other chunks; use knowledge in world to make connections - reduces the amount of information to be stored Why did researchers come to believe in STM independent of LTM? - Arthur Melton (1963) started formal arguments for the existence of STM at the APA annual meeting - theory of STM is distinct from LTM is currently controversial; some people reject theory (Sederberg, Howard, Kohana, 2008) Memory loss following brain damage - can get new information into STM but not LTM? - HM is most famous patient - had access to some of old memories (childhood); could not learn new memories - surgery to relieve severe epilepsy in 1953, at age 27 - bilateral excision of medial temporal lobe - "it's like waking from a dream" - anterograde amnesia: inability to remember things that happened after brain damage. Implies inability to transfer new memories from STM into LTM - retrograde amnesia: inability to remember things that happened before brain damage. Implies inability to retrieve existing memories from LTM - Scoville and Milner (1957); after surgery, profound anterograde amnesia; also showed some retrograde amnesia - studies by Brenda Milner: - good vocabulary and language, normal IQ, no attention disorder - things unable to learn: - where he lived, who cared for him, what he ate at his last meal, the year, president, age, failed to recognize himself on his 40th birthday in 1982 - somehow learned that, in the 1970s sitcom All in the Family, Archie Bunker's son-in-law was called "Meathead"; possibly done by residual of hippocampus - could not learn declarative tasks: photographs of people, verbal material, sequences of digits, nonsense patterns, complex geometric designs, could not expand his digit span - showed procedural learning: improved with practice (procedural memory) but denied having that practice (declarative memory) - Milner (1962) trained HM on a mirror-drawing task - Cohen and Corkin (1981); HM showed procedural learning on Tower of Hanoi puzzle - consensus was that LTM was impaired but his STM spared Capacity - capacity of LTM is essentially infinite (can always learn), what about STM? - Shepard and Teghtsoonian (1961); present 200 three-digit numbers in a row - task: say when you hear a repeated number - IV: interval before repetition; DV: probability of noticing repetition - forgetting function: how does probability of noticing repetition vary with interval? - are there separate forgetting functions for STM and LTM - probability of noticing repetition fell dramatically at first - steep decline in probability ended at interval = 7 items (between first and second appearance) - probability of noticing then fell more gradually, asymptoting at 60% - initial steep decline occurs because response comes from STM (decays quickly) - more gradual decline occurs when response depends upon LTM (slow decay, if at all) - different slopes represent different forgetting functions so different storages Why should STM have so small a capacity? - sensory and LTM both have large capacity - if STM was any larger, it would take too long to search through; need it fast Duration - LTM lasts a long time (Bahrick 1984 - permastore) - Brown (1958) and Peterson and Peterson (1959) - task: subjects see a stimulus and have to recall it after an interval - rehearsal is prevented by having them count backwards during retention interval - IV: length of interval in seconds - result: interval longer than 18 seconds, no longer remember - memory system where things must be rehearsed or are soon lost, but do not rehearse in LTM so STM must be different from LTM - criticism: counting backwards may interfere with STM - STM is at most 30 seconds Type of Code - every stimulus has multiple aspects; colour, brightness, shape, surface texture, category, name; All found in LTM, are all in STM? - Brown/Peterson paradigm - task: subjects briefly see a stimulus and have to recall it after an
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