Ch. 3 - Short-term memory

Digit span

Digit span

Maximum number of sequentially presented digits that can reliably be recalled in the correct order. Reflect short-term memory.

Working memory span

Term applied to a range of complex memory span tasks in which simultaneous storage and processing is required. Reflect working memory

Short-term memory (STM)

Refer to performance on a particular type of task, one involving the simple retention of small amounts of information, tested either immediately or after a short delay.

Working memory

A system that not only temporarily stores information but also manipulates it so as to allow people to perform such complex activities as reasoning, learning, and comprehension.

Memory span measures require two things: 

1. Remembering what the items are

2. Remembering the order in which they were presented

Things that affect memory span

• In the case of the digits, we already know the items very well, so the test becomes principally one of memory for order.

• If an order of letters in the sequence allowed you to break it up into pronounceable word-like subgroups or chunks.

C T A I I L T C S F R O vs. F R A C T O L I S T I C

Chunking

The process of combining a number of items into a single chunk typically on the basis of long-term memory. Proof that LTM can influence STM. Grouping can also be induced by the rhythm with which a sequence of items is presented.

The modal model

1. Flow of information from the environment 

2. Into a series of parallel sensory memory systems, the iconic and echoic systems

3. From here it enters a short-term memory store which also serves as a “working memory” capable of both storing and manipulating material 

4. Which is then fed into a more durable long-term store.

Phonological loop

Term applied by Baddeley and Hitch to the component of their model responsible for the temporary storage of speechlike information.

Phonological similarity effect

A tendency for immediate serial recall of verbal material to be reduced, when the items are similar in sound.

Articulatory suppression

A technique for disrupting verbal rehearsal by requiring participants to continuously repeat a spoken item. The subvocal rehearsal system can be blocked if you are required to repeatedly say something unrelated.

Word length effect

A tendency for verbal memory span to decrease when longer words are used.

Irrelevant sound effect

A tendency for verbal STM to be disrupted by concurrent fluctuating sounds, including both speech and music.

Changing State hypothesis

This assumes that retention of serial order can be disrupted by irrelevant auditory stimuli provided that these fluctuate over time

The problem of serial order

The purely verbally specified phonological loop model had two major shortcomings. 

1. No adequate explanation of how serial order is stored. 

   • Given that the classic digit-span task principally involves retaining serial order, this is clearly a major limitation. 

2. Second, the model had no clear specification of the crucial processes involved in retrieval from the phonological store. 

Free recall

A method whereby participants are presented with a sequence of items which they are subsequently required to recall in any order they wish.

Recency effect

A tendency for the last few items in a list to be well recalled during free recall.

Primacy effect

A tendency for the first few items in a sequence to be better recalled than most of the following items during free recall.

LTM variables studied include:

1. Presentation rate: slower is better

2. Word frequency: familiar words are easier

3. Imageability of the words: words that are visualizable are better

4. Age of the participant: young adults remember more than children or the elderly

5. Physiological state: drugs such as marijuana and alcohol impair performance.

Long-term recency

A tendency for the last few items to be well recalled under conditions of long-term memory.

Two aspects of visual working memory

1. Spatial memory (where?) 

2. Memory for objects (what?)

Active rehearsal in visual STM

Visual STM appears to benefit from an active attempt to maintain an item in the focus of attention. 

What is stored in visual STM?

The visual system processes the world through a range of separate sensory channels, with shape, color, and movement for example all being detected by different neural systems. The fact that we experience an object such as a red square means that the separate features of color and shape that are present in the stimulus, must then have been recombined, allowing the separate channels encoding shape and color to be experienced as a single object, a colored square

Binding

The capacity to reunite the features of an object. The attentional disruption did not differ across conditions, suggesting that the process of binding shape and color is automatic.

The act of binding appears to be relatively automatic, although remembering is clearly not, as overall performance in all conditions suffers from the additional task. 

Visuo-spatial STM

We have made a distinction between spatial STM, remembering where, and object memory, remembering what. In practice, these two systems work together but tasks have been developed that particularly emphasize one or other of these two forms of visuo-spatial memory. Visual STM is not of course limited to remembering patterns, but also involves shapes and colors.

The Corsi test (Corsi block tapping)

Visuo-spatial counterpart to digit span involving an array of blocks that the tester taps in a sequence and the patient attempts to copy.

What limits the capacity of visual STM?

• Attentional blindness

• Fixed slots versus flexible resources

Deficits in visuo-spatial short-term memory

• Impaired performance on either visual or spatial STM

• Colors or shapes 

• Impaired visual memory coupled with a grossly impaired capacity to draw

Visuo-spatial STM

Retention of visual and/or spatial information over brief periods of time.