1Cognitive Psychology C81COG 5. Memory – Structure & Processes Dr Jonathan Stirk
2Background ReadingBaddeley, A.D. (1999). Essentials of human memory. Hove, UK: Psychology Press.Chapters 2 & 3
3Overview Dichotomies in the description of memory Memory Processes Structural attempts to separate STM and LTMforgetting by decay or interferencecapacity differencescoding by sounds or by meanings?The simple multi-store model fails, soan alternative to structural distinctions?a revised model, based upon “working memory”
4Common distinctions in the description of memory Short-term (1°) vs. Long-term memory (2°)The phone number of your dentist (look it up in the phone book, then dial it) vs.A very familiar phone number (e.g. Home)Distinction based on temporal aspects of memoryTemporary and fleeting vs. more permanent and stablePrimary memory (STM) is what is in consciousness at the present timeSecondary (LTM) is what is more permanently etched in memory
5Common distinctions in the description of memory (LTM)Procedural[non-declarative](Skills, priming, conditioning)Declarative(Knowledge)Open to intentional retrievalSquire (1992) – components of LTMMeasured through performance rather than conscious recall/recognitionEpisodicSemanticLarry Squire (1992)
6Procedural vs. Declarative LTM How to tie your shoelaces vs. the name of the current US presidentProcedural Memory: ‘knowing how’, remembering how to perform skilled actions, implicitDeclarative Memory: ‘knowing that’, explicitHow?That?
7Episodic vs. Semantic LTM What did you have for lunch today? vs. What kinds of animals are canaries?Tulving (1972) distinguished between episodic & semantic memoryTulving (2002) – “Episodic memory is about happenings in particular places at particular times or about “what”, “where” & “when”.Episodic Memory: autobiographical, temporally dated, memories of life experiencesSemantic Memory: memory for words (lexical memory), world knowledge, not temporally dated, very well-organized (organization protects memory from interference)
8Semantic Memory – Tulving (1972) “It is a mental thesaurus, organised knowledge a person possesses about words and other verbal symbols, their meanings and referents, about relations among them, and about rules, formulas, and algorithms for the manipulation of these symbols, concepts, and relations.”
9Memory ProcessesProcess - Activities taking place within memoryEncodingConverting information into a form suitable for use in memoryStorageRetaining information in memoryRetrievalBringing to mind information stored in memory
10Memory Structure - Multi-store Model (Modal model) Sensory registersShort-term storeLong-term storeStructure refers to the organization of memory/ the architectureOne model of memory is that it is structural with a number of separate stores for information (multi-store)Prior to this many assumed a single store (unitary) model of memory!! Structural distinction between STS and LTSDeveloped from numerous findings at that time in the memory literature.Sensory registers: modality specific, fast decaySTM: Limited capacity; information displacedLTM: Unlimited capacity, holds info over long period of time, prone to interferenceAnimation: 3 processes in which information is lost from 3 stores (decay, displacement, interference)Attention allows us to transfer information from sensory store to STMRehearsal allows us to transfer from STM (primary memory) to LTM (secondary memory- info left consciousness)Maintenance rehearsal- consciously repeating info (STM to LTM)Elaborative rehearsal- consciously focusing on the meaning of info (STM to LTM)- see next slideForgetting mechanismsDECAYDISPLACEMENTINTERFERENCE(Atkinson & Shiffrin,1968)
11Elaborative Rehearsal A strategy of associating a target stimulus with other information at the time of encodingI.e. Creating meaningful associationsBy creating meaning and associating meaning with other information in memory, information can be maintained in memoryWill come back to elaborative rehearsal later in ‘levels of processing’ section
12Differences Between Memory Stores Evidence for separate and distinct memory stores has been supported by looking at:Forgetting mechanism(s)Storage capacityTemporal durationEffects of brain damageIn order to justify the 3 qualitatively separate and distinct memory stores, we would expect to find major differences between them.This has been shown to be the case.
13Properties Of The Short Term Store FORGETTING MECHANISMSLoss of information through autonomous decayDistraction results in loss of information (Peterson & Peterson, 1959)LIMITED STORAGE CAPACITYSTM span limited to 3 items (pure STM capacity limit; not Miller’s 7+-2; see next slide)Recency in serial recall curve is read-out from Primary Memory (Craik, 1964)Delayed recall eliminates recency (Glanzer & Cunitz, 1966)STM loses information if it is not rehearsed by processes of forgetting (decay/displacement)Decay- the memory trace fades as a function of timeDistraction prevents rehearsal- discuss P & P study on next slideLimited to 3 items (limit to STM)- Immediate memory span which includes LTM is 7+-2 (Miller Magic Number)- allows for chunking!!Immediate memory span allows info to be transferred to LTM increasing the span. When rehearsal stopped a more accurate capacity of 3-4 items is obtained
14Chunking Allows More Information To Be Stored Miller (1956) suggested that memory capacity is not limited by number of items that can be stored but by number of chunks. Chunking requires support by LTMStoring a long phone number may be helped along by chunking information into meaningful bits as in slide. This however requires support from LTM e.g can be stored as 1 chunk – Nottingham dialling code
15Evidence for forgetting by decay in a STM task Peterson & Peterson (1959) distracter taskListen to a consonant trigram (e.g. SKB)Now start counting backwards in threes from this number (e.g. 751)Varied how long they did this for (variable delay to allow the counting to have an effect)Now recall the trigramRepeat 1-3 for more trials/trigramsQ. What % of trigrams are correctly recalled, and how is this influenced by the delay between presentation and recall?Distraction prevents rehearsal – P & P examined effects of stopping rehearsal on STM – stopping rehearsal should prevent information being passed into LTM (according to the modal model!)A trigram contains less items than the ST immediate memory span. So should be easy to remember.Presented consonant trigrams (3 letters)Count back: etc varied delay btwn presentation of trigram and recall (i.e. length of distracter task)
16Loss Of Information From STM By Decay ResultsInterpretation: We lose information from STM through autonomous decay when information is left unattended.Around the 1960’s forgetting in LTM was thought to be by interferenceSee also Brown (1958)Also known as Brown-Peterson distracter taskAbility declined to approx 50% after about 6 seconds of distracter task; after 15 sec recall close to zeroSo P&P showed rapid loss of information through trace decay.Same effect when words used instead of trigramsCompare STM to the reverberations of a bell, bang bell and hear sound for a while but it dies down unless banged againDelay between presentation of trigram & recall, during which participants are distracted by counting backwards, & during which forgetting is possible
17Glanzer & Cunitz (1966) – Further evidence of 2 stores (STS & LTS) LTMSTMUsual recency effect (about 3 items!)G & C presented 10 words to subjects and then tested free-recall immediately or after 10 & 30 seconds delay.Primacy & Recency effect – in free recall (words recalled in any order) words at beginning & end recalled betterSerial Position Curve (U-shaped) – Serial position effectThe U shape was evidence for 2 memory stores – Primacy section items made it to LTM (more time for rehearsal) , Recency section items left in STM before decayDelay effects the end part of the curve but not the middle or start:The recency effect is eliminated by delay in a Brown-Peterson distracter task (see orange)-trace decay due to no rehearsalSo Recency effect is caused by read-out form Short Term Memory storeRest of curve represents read-out from LTMRecency effect is eliminated by delayPrimacy Effect
18Other factors effecting the serial-position curve: Word Frequency & STM high freq (common)low freq (rare)LTMSTMUnlike delay, word frequency seems to effect the beginning and middle parts of the curve but NOT the endMore frequent/common words recalled betterWord frequency affects recall from LTM but not STM (Raymond, 1969; )Common words have better established meanings which are stored in LTMRaymond, 1969
19Double Dissociation The primacy effect is altered by Double Dissociation: two situations or theoretical entities are affected in opposite ways by one or more independent variablesThe primacy effect is altered byThe word frequency of items used in the taskLow frequency words → lower recall of first few items in listThe recency effect is altered bythe use of a delay between learning & recalldistracter task → lower recall of last items in listThe previous 2 slides show an example of a Double Dissociation: two situations or theoretical entities are affected in opposite ways by one or more independent variables (e.g., distraction affects WM but not LTM; word frequency affects LTM but not WM)if we can influence primacy without recency ANDwe can influence recency without primacyBut NOT by a delay!But NOT by word frequency!
20Recall These 8 Letters In Order V C B D G E P TR F Q P L N Z KAsk class to recall letters in order –click appear then click disappear!Did they do better in List 1
21Did you perform better for list 2? Recall These 8 Letters In OrderV C B D G E P TR F Q P L N Z KDid you perform better for list 2?
22Further Properties Of The Short Term Store CodingCoding in LTM is thought to be semantic (based on meaning)/associative.What about coding in STM then?Evidence for Acoustic codingConfusions in recall between items which have similar sounds (Conrad, 1964; RLTKSJ →RLCKSA)Categorical but non-associative storageMeaningful relationships between words are not appreciated (Tulving & Patterson, 1968; )Evidence that the code is acoustic/phonological. Conrad (1964) – found that when recalling letters in a 6 letter stimulus people made substitutions with similar sounding lettersUnlike Iconic memory, code is categorical- words can be assigned to semantic classes e.g. Letters( consonants vowel consonant), numbers.T & P (1968) lists of words to free-recall, some lists contained 4 semantically related words (arm, hand, leg, foot)C – Unrelated words, E – Related words form a group at the end of the list (STM), M – Group in middle (LTM), D – distributedFindings: related words retrieved from LTM as a single unit from the M list but not the E list.Unitization of related words much smaller in E(nd) lists. Semantic relationships between words NOT coded in STM!
23Summary of Properties Of STM The short-term store retains a limited amount of information for a brief interval, and what it retains is categorical but non-associative items using an acoustic codeLimited capacityShort duration (information lost by decay if not rehearsed)Phonologically codedMore common words recalled better ( common words have better established meanings – stored in LTM)
24Problems With Earlier Interpretation of Peterson & Peterson’s (1959) exp’t! Keppel & Underwood (1962)An average taken for each subject across numerous trialsThis assumes no performance change across trialsNo forgetting on trial 1, some on 2, more on 3After an 18 sec delay, PI from triplets presented on earlier trials builds up.Pro-active interference/inhibition (interference from info presented before the to be remembered info)So it;s looking like STM and LTM have different properties, suggesting that they are separate distinguishable stores. BUT!!!!!K & U suggested that interference could explain the results!Interference theory stemmed from work of SINGLE MODEL THEORISTSUsed the same technique as P & P but looked at trial by trial analysis.NO forgetting apparent on trial 1, despite the large delayAt this stage there was evidence to support both single and multi-models of memory.So as STM may use interference as a mechanism for forgetting it is now looking very similar to LTM!!!!!!
25Problem: Evidence of Semantic Coding In a STM task Warren & Warren (1976)S hears PRINCE, KNIGHT, QUEEN (the “memory set”)10 seconds of a distracter taskSubject recalls the “memory set” (“Prince…”)Next trial sometimes contains a homophone-related set e.g. MORNING, NOON, EVENING10 seconds of distraction, etc, etcQuestion - Do subjects ever confuse KNIGHT and NIGHT in the recall of the homophone-related set? (Is night offered in error in the recall of MORNING, NOON, EVENING?)Answer - YES, therefore there has been some semantic processing of these words even though they are in a STM taskBy the early 1970’s the Atkinson & Shifrin 3 stage structural model was being questioned.Patients with poor short term memory still could lay down detailed long term memories. This shouldn’t happen according to 3 stage model as rehearsal in STM should be necessary to transfer to LTM.So for STM the code seems acoustic but is there evidence of coding by meaning (semantic coding)?W&W seemed to show that there is evidence of semantic processing.Suggests that the idea of a multi-modal model may be flawed and that we needed something else.
26Separate Properties?So, is STM a “pure” system, with its own forgetting/coding characteristics, or does it share its properties with LTM?A qualitative difference from a quantitative change?Oxidation of silver over timeAfter 10 minutes (insensitive method)After 10 months (now more sensitive)The same process is at work, but the effects appear to be different over different time intervalsPerhaps the methods of studying forgetting/coding are also insensitive and have also given misleading conclusionsWe assume from the data / studies that quantitative differences mean qualitative difference between STM & LTMWe can compare this with looking at oxidation of silver- nothing seems to be going off over 10 minutes but after 10 months there are noticeable differences.
27Separate Stores? So evidence for 2 separate stores is not conclusive! Rather than focusing on structure, why not look at the processing of information instead?Craik & Tulving (1975)
28Levels Of Processing Approach (Craik & Tulving, 1975) Structural model breaks downAtkinson & Shiffrin (1968)Rehearsal always enhances transfer to LTMNot true!Remembering is influenced by the “level of processing” during input (e.g. visual processing vs. semantic processing)The emphasis is now upon process rather than structureSuch evidence was making it harder to argue for separate structural distinctions between STM & LTM.A newer approach was to look primarily at the processes rather than the structure of memoryC&T argued that nature of processing affects how effectively info is transferred and stored in LTM
29Craik & Lockhart (1972)- Levels of processing hypothesis Depth of processing predicts durability of memoryCraig & Tulving (1975) - List of visually presented, unrelated words.3 groups each with a different decision task1. Is the word in CAPITALS?2. Does it rhyme with “ate"?3. Is it a type of fish? Or does the word fit into the following sentence?Measured latency (decision time)Then surprise memory test – recognition from list of targets & distractersDistinguished between shallow( e.g. detecting specific letters in words, physical characteristics) and deep/semantic processing (meaning)C&T did a number of exp’ts (10) to investigate their levels of processing theoryC &T had subjects make various decisions about unrelated words presented to themVisual processingAcoustic processingSemantic processing
30Craik & Tulving’s Results As the depth of processing increases decisions take longer to make (latencies increase – red figures)andUnexpected recognition improves (blue bars)0.7460.689Increased depth of processing improves recognitionAmount of processing is also importantIncreased latencies infer increased depth of processingThey also looked at Recall as well as recognition and also found same affect0.614RED = latencies (secs)
31Updating The Multi-store Model Of Memory Baddeley & Hitch (1974)Model emphasises both storage AND processingNot unitary – verbal /visual-spatial subsystemsOriginal incarnation was tripartite (3 components)The shift towards focus more on process rather than structure prompted Alan Baddeley to suggest a newer and more intricate model of STM which he named his “working memory” modelShifted the emphasis from passive storage (short-term memory) to active processing (working memory)Purpose of STM was to hold information so it could be worked onWM not a unitary system- has separate verbal and visual-spatial subsystems
32Working MemoryCentral executive: directs and controls all WM functions; can be thought of as ‘attention’. Integrates infoVisuospatial scratchpad/sketchpad: a system for holding visual informationArticulatory/phonological loop: a system for holding and recycling auditory/acoustic informationRehearsal/Articulatory loop : a process for recycling, using subvocalizationPhonological buffer/store: a structure for holding acoustic informationEach component is capacity limitedArticulatory loop & VSSP are modal, whereas CE is modality independent and whether CE is a unitary system or has multi-components.
33Working Memory Updates Later version (Baddeley, 2000) incorporate an “episodic buffer” which time-stamps memoriesSo we know when something happened and not just that it happenedLater versions split the articulatory loop and visuo-spatial sketch pad into two dual slave systems which are used by the CEStill problems with this model though.Little known about the CE and its precise functions