5 Human Memory Encoding

8/19/2019 5 Human Memory Encoding

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Human Memory Encoding,Storage, Retention, and RetrievalMemory is retention of information over a period of time. Ebbinghausstudied memories by teaching himself lists of nonsense words and thenstudying his ret ention of these lists over p eriods of hours to days. This

was one of the earliest studies of mory

Contents:

1.Short Term Memory2.Working Memory

3.Long Term Memory4.Spreading Activation Model5.Practice and Strength6.Depth of Processing7.Elaborative Processing and Text8.Forgetting: Gone or I naccessible?9.Forgetting: Decay or I nterference?10. Retrieval and Inference11. Other Facts about Memory

Short Term Memory

While Ebbinghaus studied retention over long intervals, laterexperiments studied memory loss over periods of seconds to minutes.Short term memory was postulated to explain temporary retention ofinformation as distinct from long term retention of information. Shortterm memory acts to also store current sensory information and torehearse new information from sensory buffers. It h as limited capacity(Miller's 7 plus or minus 2). The probability of encoding in Long termmemory has b een directly related to time in short term memory.

It is now believed that t he loss of information stored in short t ermmemory has the same characteristics as loss of information stored inlong term memory. It happens quicker becau se it involves informationthat is not learned as well. What we call the learning process istransferring information from short term to long term memory an d is a


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physiological process. The shape of the memory loss curves are thesame. Hence we don't need to postulate a special type of memory.Instead, we n eed a t heory o f:

• Why we can rehearse only a limited amount of information at atime.

• How different memories get different strengths (and so areforgotten at differen t rates).

Working Memory

Here we address w hy we can rehearse only limited information at a time.

Articulatory Loop Rehearsal limitations are d ue to limits in how long ittakes verbal material to decay, not how many items we can store. Hence,the faster we can rehearse, the more we can store (Baddeley, 1986).Experimental support: word length effect. How long it takes to read

words predicts how many words will be remembered. Articulatory loop icalled the phonological loop due to evidence that i t involves sp eech. Wecan rehearse about 1.5 seconds of verbal material before i t decays. Timein the loop is not related to probability of coding in long term memory.Baddeley's model proposes that we have a vi sual/spatial sketchpad as

well as the phonological loop. These hold

executive. There i s ev idence that a particular area of the frontal cortex isinvolved in working memory.

Long Term Memory

A simple observation: we often need to recallong ago. How quickly and reliably we recall it depends o n:

• Activation: How long since we last used the information.• Strength: How well we h ave p racticed it.

Experimental Evidence: (Anderson 1976) - Subjects learn somesentences. Some sen tences are s tudied twice a s long as others. Subjectsmust discriminate sentences they learned from distracters. They aretested for each sentence more than once, with varying interveningsentences. Results: Both amount of study and how recently the


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information was accessed affect speed of response. However amount ofstudy matters only if the information was not recently accessed (aninteraction effect).

Delay (number of interveningitems)

Degree of Study

Less Study More StudyShort (0-2) 1.11 seconds 1.10 secondsLong (3 or more) 1.53 seconds 1.38 seconds

Spreading Activation Model

When information becomes easier to access as a result of having beenused recently, we say it is more activated. This activation spreads

between semantically related concepts.

Empirical Evidence:

• Subjects are faster at c onrming that a pair of words are both words if the second word is an associate of the rst, for example, bread and butter (Meyer and Schvaneveldt 1971).

•

Given a word, subjects a re asked to give an associated word. Theirresponse is faster if subjects have responded with an associated word on a previous trial (Perlmutter and Anderson, gure 6.8).

• Speed of activation seems to be about 200ms (as measured byRatcliff and McKoon, 1981).

Implication: Text is ea sier t o rea d if semantically rel ated words a re u sed.

Practice and Strength

We've seen that speed of recall of information femorydepends in part on how recently that information has been activated.However, what about the fact that speed of recall also depends onamount of practice? Activation changes quickly over time. The effect ofpractice decays much more slowly over time (witness Ebbinghaus, thealphabet). Thus t hese are b elieved to be d istinct processes.


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Power Law of Learning

A very robust result: the effect of practitasks ts a p ower law

Reaction Time equals C * Practice Time K where C and K are constantsthat depend on the task.

Practice h elps a lot at rst, then provides decreasing gains as you reachthe l imits o f your p erformance ability.

Long-Term Potentiation - There appears t o be a neural basis for t his lawof learning. Neural pathways in the hippocampus (known to be involvedin learning) become increasingly sensitive when stimulated. The change

in sensitivity follows a power l aw relationship.

Depth of Processing

Craik and Lockhart (1972) proposed that strength of memory depends onhow deeply information is p rocessed, not on how long it is p rocessed

Experimental support: Memory for words not improved by merelyrepeating them for a longer p eriod of time (Glenberg et al. 1977). A largenumber of studies su pport the depth of processing conclusion. It appliesto subject matter l earning as well as laboratory situations. Subsequent

work focused on what constitutes deep processing.

Processing Meaning:

Some lab studies compare tasks that require processing meaning of words versus form (e.g., what letters

Elaborative Processing and Text

Studies show benets of connecting the items to be remembered to otherrelated information (e.g., elaborating on sentences t o be rem embered, orrhyming). Intention does not matter. Subjects in deeper processingconditions do better regardless o f whether t hey know they will need toremember the processed items.


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Implications for study habits and method.

1.Preview the m aterial2.Make up questions3.Read, trying to answer the qu estions4.Reect while you read. think of examples, relate it to what you

know.5. Recite the information in each section after you 've read it. Re-read

what6. you can't recall.7.Review the major points an d the answers to your questions at the

end.

• Question generation is a t least as b enecial as qu estion answering.•

Questions generated before the material rather t han after m ay bemore benecial

Forgetting: Gone, or Inaccessible

Do we forget because the information is gon e, or do w e forget because wecan't ac cess information that i s still there? It i s difficult t o distinguishthe two. However, there is evidence that we retain more than we canretrieve.

Experiment: (Nelson 1971) - L earn paired associates (numbers tonouns). Tested 2 weeks later to see which were remembered. Then givennew material to learn that had some of the forgotten numbers, both withand without their or iginal nouns.

Results: Subjects relearned the original associations faster (in spite ofthe fact that they co uld not recall them). Subjects rel earned the originalassociations faster ( in spite of the fact t hat they could not r ecall them).

This suggests that some associative information was retained. One

possible interpretation: s trength of m emories decay gradually. If thesestrengths fall below a certain threshold, we can't r ecall the information,

but the remaining memory trace is still

Forgetting: Decay or Interference?


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Is forgetting due t o decay of unused information, or t o interference of newinformation with old information? Different kinds o f evidence a re offeredfor ea ch position.

A survey of forgetting research concluded thainformation usually conforms to a power law: we forget a lot at rs t, butover t ime th e ra te o f forgetting diminishes.

Decrease in long-term potentiation follows a similar power law. Thesefacts a re interpreted by so me a s evi dence for a physiologically determineddecay ra te.

Interference Experiments Typical Experiment (A-D C-D paradigm):

1.Subjects all learn A-B association (between items on list A anditems o n list B).2.Experimental subjects learn A-D associations (which use the same

stimuli items as the A-B associations), while control subjects learnC-D association.

3.Everyone is t ested on A-B associations.

Typical Results: Experimental subjects t ake longer t o learn their secon dset of associations than controls, and make more errors on the A-B test.Experimental subjects take longer to learn their second set of

associations than controls, and make more errors on the A-B test. Theseresults are interpreted as evidence that learning new associations tostimuli causes forgetting of ol d associations. However, interference doesnot happen with factual material when the additional facts areredundant with (e.g., causally related to) the original facts.

Fan Effect (a model) - Interference effects can be modeled as weakeningof spreading activation over m ultiple links in a propositional network.

Stimulus activates concept n odes.- F ixed (limited) amount of activationspreads from activated nodes over associative links, d ivided equally

between links. (Hence the more links, the less activation per l Activation converges at propositional nodes (candidat

one emerges as the answer. Time to identify the response is inverselyrelated to level of activation.


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Decay or Interference? Some claim that interference can produce theappearance of decay although it appears, both mechanisms a re involvedin forgetting or memory l oss.

Retrieval and InferenceIt is well established that people make inferences during retrieval, and

believe that they saw or heard things tmore likely to erroneously think they read a sentence if it is animplication of something they read .

Effect of Prior Knowledge - People add other knowledge they have aboutthe m aterial studied.

Effect of Question Wording - Subjects shown lm of automobileaccident. Subjects ask ed: Did you see a b roken headlight? or D id you seethe b roken headlight? (There was actually none.) Results: Subjects morelikely to respond yes to th e broken headlight. Implications for co urtroomtestimony!

Other Facts about Memory

Organization of Material

Retrieval of information is better i f the information is organized in somemanner supporting syst ematic searc h, such as in hierarchies.

Method of Loci

The ancients remembered things by imagining taking a familiar walk,and placing the things to be remembered at locations along the way. Thismethod works because it organizes the material to be remembered and it

encourages el aborative processing and memorable imagery.

Context-Dependent Learning

Physical and emotional context may be inadvertently coded as retrievalcues, along with the intended cues.


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Consistent with this idea, various st udies sh ow that recall is b etter w hentested in the same context (physical or em otional) as in which learningtook place. Some benet has b een found studying for important exams inthe sam e room as t hey will be taken. However these r esults are variable.

5 Human Memory Encoding

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