Short-Term Memory

Short-Term Memory

A demonstration

Additional physiological evidence:

·         Hippocampal Lesion Evidence

o        Sperry and Gazzaniga

What is the Capacity of STM?
How does Forgetting occur in STM?
What is the Mental Code ("mentalese") of STM?
What is the role of Rehearsal in transfering information from STM to LTM?

Baddeley's Working Memory Model

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The Capacity of Short-Term Memory

An example

Miller (1956) believed that the "span" of STM was 7 + or - 2 chunks.

What is a chunk?

·         A chunk is a cluster of items that have been previously stored as a unit in long- term memory.

Issues in Chunking:

·         Relationship of short-term memory span to intelligence

·         Exceptional STM

·         Expertise and STM:

o        Master vs. weak chess players.


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Forgetting in Short-Term Memory

Peterson & Peterson (1959)--The rate of forgetting in STM
Basic Methods:

·         S's were given 3 consonants to try to remember (SBJ).

·         S's were given a 3 digit number (394) & asked to count backwards by threes from this number (e.g., 391, 388, 385, . . . ).

·         After a variable amount of time counting, S's were asked to recall the 3 letters.


Conclusion: This seems to indicate that STM fades away after approximately 12 seconds without rehearsal.

Waugh & Norman (1965) suggested that it could be that the counting backwards is interfering with STM recall. They designed an experiment to try to separate decay theories of forgetting from interference theories.


·         S's were presented w/ lists of 16 digits. S's task was to remember the prior presentation of the last digit and to recall the digit that followed it in the list earlier.

·         For example: 7 4 4 1 2 9 5 7 5 3 4 2 8 7 6 8

·         The numbers were read at one of two rates: 1 digit per second or 4 digits per second.

Predicted Results if Decay Theory is correct.

Predicted Results if Interference Theory is correct.

Actual Results:

Conclusion: Interference seems to play a bigger role in forgetting in STM than memory decay. The type of interference found in this experiment is called retroactive interference.

Proactive Interference also occurs.

·         Proactive interference refers to forgetting that occurs due to prior learning.

Keppel & Underwood (1962)

·         They replicated the Peterson & Peterson Task keeping the time delay constant (e.g. 12 seconds).

·         They analyzed their data by trial number (1st trial, 2nd trial, 3rd trial, etc.).


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The Mentalese of Short-Term Memory

Conrad (1964)
He performed the Peterson & Peterson Task using the letters B C P T V & F M N S X and looked at the error patterns when S's recalled the wrong letters.
He found that 75% of the errors were from the same acoustical class suggesting that STM mostly contains acoustical information.

However, Brooks (1968) showed that visual/spatial information must exist too.


Also, Wickens (1970) showed that semantic information may be important to STM.

The Release from Proactive Interference

Wickens replicated Keppel & Underwood's experiment but changed the category of the memory items on the 4th trial for some subjects. (e.g., changing from letters to words or vice versa).

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The Role of Rehearsal in Transfer from Short-Term Memory to Long-Term Memory

Atkinson & Shiffrin suggested that information was transferred from STM to LTM through rehearsal.

·         Rehearsal = Verbal repetition of information.

Early research by Rundus (1971) supported this claim.

·         Rundus conducted a standard learning paradigm in which S's heard a long list of words to try to remember.

·         S's were instructed to talk aloud while learning these words.

·         After the list presentation, S's counted backwards by 3's for 30 sec. to clear out their STM.

·         He found that the more times a S repeated a word during learning, the greater that S's memory for that word was suggesting repetition led to transfer to LTM


Craik & Watkins (1973) suggested that mere repetition wasn't enough to tranfer information to LTM.

·         In their expt, they required S's to only hold one word in STM at a time, and they varied the amount of time the word was held in mind.

·         S's were told to remember the last word they heard that started with the letter G and were given a 21 word list.

·         Rehearsal time was varied by manipulating how long it was between words that started with G. (e.g., daughter, oil, rifle, garden, grain, football, table, anchor, giraffe --"garden" would be held for 1 second, "grain" for 4 seconds, etc.).

·         After 27 lists, S's had to recall all the G words.

Results: No correlation was found between amount of time in rehearsal and later recall.

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Baddeley's Working Memory Model

In Baddeley's model, we see a shift away from emphasizing the structure of memory to an emphasis on the processes of how information gets into and out of memory.

Research examples: Baddeley & Hitch (1974)

Expt1 Methods: S's perform two tasks simultaneously.

·         A difficult or easy standard STM task. Remember & repeat either 6 random digits or 1,2,3,4,5,6 over and over.

·         A simple reasoning task. S's had to judge the veracity of simple sentences like:

o        A is not preceded by B.

o        AB


Expt2 Methods:

·         S's hear a prose passage.

·         S's see digits on a computer screen & either:

o        write them down as they see them or

o        write 6 of them down after seeing the 6th one

·         S's are then given a prose comprehension test.


Conclusion: Performing mental reasoning and language comprehension utilize the same mental resources as STM and should be thought of as involving many of the same processes.

Independence of the Visuospatial Sketchpad and the Articulatory Loop:

Use tasks that occupy VSSP or AS but take little mental effort (i.e., Central Executive resources) and look at how these affect performing visual or auditory STM tasks.

·     Visual – Perceptual Vigilance task

·     Auditory – Articulatory Suppression task

These tasks disrupt STM performance in the same modality but not in the other modality.

Individual differences in Working Memory Capacity

Feldman-Barrett, Tugade, & Engle (2004) showed that WMC is highly related to how people do on a whole bunch of tasks.

Their findings across 20-30 publications is that WMC affects the amount of automatic or controlled processes that people use.  Individuals with high WMC use more Controlled processes; individuals with low WMC use more Automatic processes.

This fits with a wide variety of dual-process models of cognition & behavior.


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