SHORT-TERM RETENTION
CHAPTER 8

I. GENERAL ISSUES

A. Short-term memory (STM) deals with the information storage system that has a limited capacity and duration, and is typically studied in contrast to long-term memory (LTM), which has virtually no capacity or duration-based restrictions.

B. STM is critical for virtually everything we do, as it serves as a mental workspace that is used and reused constantly.

II. DEFINITIONS

A. William James, one of the American founders of Psychology, made an early distinction between what is now referred to as STM and LTM. James referred to these processes as primary and secondary memory.

1. Primary memory is information that is currently in one’s consciousness.

2. Secondary memory is absent from current consciousness and is part of one’s psychological past.

B. Waugh & Norman added to our knowledge of memory by arguing that recall can come from either primary or secondary memory.

C. Atkinson & Shiffrin (1968) developed what has come to be known as the “modal model” of memory.

1. The Short Term Store (STS) is responsible for temporary processing, governed by Working Memory control processes.

2. The Long Term Store is a permanent storage system, receiving data from STS.

III. SHORT-TERM MEMORY TASKS

A. One way that STM ability is assessed is via the implementation of the Brown-Peterson task.

1. The task requires subjects to attend to some type of stimulus (e.g., a set of words, a nonsense syllable, etc.), and then after presentation of the stimulus, subjects are required to count backwards by 3s from a given number (e.g., 124).

2. After a given amount of time (e.g., 3, 9, 12 seconds), subjects are told to stop counting and recall the initially presented stimulus.

3. Performance on the task reveals how much (or little) information can be held in STM without rehearsal (the counting task, ideally, acts as a distractor, preventing rehearsal of the critical stimulus).

B. Although the lack of rehearsal is one explanation for the memory loss demonstrated on the Brown-Peterson task, other possibilities stem from interference.

1. Proactive interference occurs when one’s memory to retain information is prevented by information that is encountered before the critical information is presented.

C. Beyond the Brown-Peterson task, the Memory Span task is also used to assess STM.

1. Memory Span is defined as the longest sequence of information that can be accurately recalled, in order of initial presentation.

2. An example of the task would be to present a sequence of random numbers to a subject, and, without delay, have then recall the sequence following the presentation of the final number in the sequence.

3. The maximum span for a healthy adult is in the range of 5-9 items (although there have been a few extraordinary individuals over the years who have had memory spans well above this!).

 George Miller (1956)—“The magic number seven, plus or minus two"

       Two main findings: 

       (a) Ss are unable to identify a set of items that vary along only one dimension if there are more than a few items

  (b) Chunking 

  Increase capacity of short-term memory by grouping individual units of information into meaningful units.

4. One limitation to memory span is the Word Length Effect, which basically argues that longer words are more difficult to recall than shorter words (e.g., short words (man, dog) are recalled better than long words (gentleman, canine)).

 Baddeley, Thomson, and Buchanan (1975)--word length and pronunciation time. 

 As the number of syllables in the words increased, the proportion of words that could be recalled decreased.

        Results--linear relationship between how long it takes to pronounce a word and the level of recall.

         Working Memory explanation--number of items that can be immediately recalled depends on how often each item can be subvocally rehearsed by the articulatory control process

The shorter the items, the more items can be rehearsed before a particular trace decays. 

5. Other individual differences, such as one’s familiarity with the stimuli, may also play a role in the size of one’s memory span.

IV. CHARACTERISTICS OF VERBAL SHORT-TERM RETENTION

A. A variety of features have been found to differentiate STM from LTM.

1. Much, although not all, of the encoding that occurs in STM is acoustic, whereas LTM tends to be more semantic.

2. STM’s capacity is limited to 5-9 pieces of information, whereas LTM is virtually limitless.

3. The duration that information can be held in STM, without rehearsal, is approximately 15-30 seconds.

4. Forgetting in STM can occur due to a fading of the memory trace, which causes the memory to not exist. In LTM, by contrast, forgetting is based more on interference or retrieval problems, which means that the memory exists, but is just blocked.

V. OTHER MODALITIES OF SHORT-TERM MEMORY

A. Beyond the typical acoustic code, information in STM can be encoded in a variety of other ways.

1. Visual Imagery codes

2. Spatial codes

3. Motor/Action codes

4. Olfactory codes

VI. WORKING MEMORY

A. Working memory elaborates on the concept of STM by including both a place for storage of information, as well as a way in which to control those storage systems and process information.

Does STS really serve as a general, unitary working memory where storage and manipulation compete for space in a limited capacity STS?

Evidence:

 Use dual-task technique--S is required to perform one task that absorbs most of the capacity of his/her working memory, while at the same time performing learning, reasoning or comprehension tasks.

Assumption: Performing a concurrent STM task should lead to a dramatic impairment in performance.

       Baddeley (1986)--Ss were required to remember number sequences ranging from zero to eight digits in length, while at the same time performing a reasoning test. 

     Effect of concurrent memory load on the speed and accuracy with which Ss performed the syntactic reasoning test:

Results: (1) reasoning time increases clearly and systematically with concurrent memory load (2) The effect, however, is not catastrophic.

If STS is a unitary system, a concurrent load of eight digits should cause reasoning performance to break down completely.  It does not.

So earlier concept of a unitary STS is challenged and replaced by a multi-component working memory model. The limits of digit span may be set by one of a number of subsystems, leaving other components of working memory relatively unimpaired.

B. Noting that STM seemed a bit restrictive, Baddeley & Hitch (1974) proposed that STM be altered into what they called Working Memory, which has several components.

1. The Phonological Loop is responsible for the immediate storage and rehearsal of verbal information.

a. This is comparable to verbal Short Term Memory.

Purpose: account for evidence regarding importance of speech coding in STM 

Phonological loop =  phonological store + articulatory control process

 Helps to explain the following phenomena:

(1) Phonological similarity effect-- memory is worse for items that sound alike than for items that differ. 

PGTCD is harder to recall from memory than the sequence RHXKW

Assumed to occur because the store is based on a phonological code, so similar items will have similar codes.  Recall will require discriminating among the memory traces.  Similar traces will be harder to discriminate, leading to a lower level of recall.

2. The Visuospatial Sketchpad is responsible for processing images and other spatial information.

a. This is comparable to visual and spatial Short Term Memory systems; research suggests that these are indeed separate processing mechanisms.

3. The Episodic Buffer acts as a bridge between information in phonological or visuospatial memory and LTM.

a. This system is a relatively new addition to the classic Working Memory model.

b. The Buffer integrates information across the phonological/visual stores, the central executive, and LTM.

4. The Central Executive controls the different subsystems of Working Memory by directing attentional resources to the subsystems as needed.

C. Working Memory & Consciousness

1. Consciousness, although not part of Working Memory, has been implicated as directing the functioning of the components of this system.

2. A related issue is the consciousness binding problem, which attempts to understand how the mind integrates what is represented in different coding forms (e.g., visual, verbal, etc.).

Phonological loop activity
            Sketchpad activity

VII. INDIVIDUAL DIFFERENCES IN WORKING MEMORY

A. The aging process influences Working Memory.

1. Aging tends to slow down the rate at which information is processed.

2. Aging also seems to inhibit one’s ability to screen out irrelevant information, resulting in the Central Executive system using attentional resource in a nonproductive manner.

3. The lack of attentional control also leads weaker encoding of critical information.

B. One’s anxiety level can also impact the functioning of Working Memory.

1. The activation of a negative mental stereotype, when perceived by a person who is the target of the stereotype, has been found to compromise Working Memory in the affected individual.

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