Short term memory + research modules 7

MBB1

Short term memory

• our conscious representation of ‘the present moment’

• a temporary store in which we integrate current sensory experiences with long-term memory to achieve current goals

• capacity

  • limited

• duration

  • 15-30 seconds

Measuring verbal short term memory capacity

• assessed using digit-span task

  • immediate serial recall of verbally presented digits (i.e., number names) in the order the were presented

  • the length of sequence is increased by one item after each successful attempt to determine the upper limit or “span”

  • A participant’s span is reached when they fail on two trails at a given series length

  • So, if you were unable to recall both trials for a series of 8 items, then your digit span would be 7 items

• Average adult span is 7 (± 2) items

  • “Seven plus or minus two” items of information

Duration of short memory

• the Brown- Peterson task

• recall the names of 3 consonants

  • (e.g.,”D-P-R”)

• Memory probed (tested) at 3-second retention intervals

• To prevent rehearsal, participants were required to count backwards from a given number in 3’s until told to stop

  • i.e., a “filled retention interval”

• For example: Participants hear “D-P-R- 306”

  • Count backwards (aloud) from 306 until asked to recall the sequence of letter names

Maintenance rehearsal and transfer to long term memory

verbal rehearsal keeps information active in short term memory and strengthens the trace to increase the chance it will be stored in long term memory

Serial position effects and transfer to LTM

• immediate free recall of lists of numbers or words is affected by the position of items in the studied list

• primacy effect

• recency effect

Primacy effect

provides evidence for transfer to long term memory for items that receive more rehearsal

Recency effect

• reflects availability of information still in short term memory

  • is reduced by introducing a filled retention interval before recall

  • are eliminated if rehearsal is prevented by introducing a concurrent task

Towards ‘working memory’: levels of processing

• the purpose of a short term memory is to encode information meaningfully

• meaningful, or “deep”, processing of information during encoding will produce long-term memory traces

• ‘shallow’ processing is less effective for long-term retention

• Craik& Tulving (1975) test this hypothesis with their study of level of processing

  • test the idea that long term memory for words is influenced by the depth (level) of the encoding process used in STM

A shift from short term memory to working memory

• studies like Craik and Tulving’s suggested the need for a more detailed account of short term memory as a multi-component system that supports meaningful encoding and active reasoning and problem solving

• Rather than focusing on maintaining information for immediate recall, the focus shifts to thinking about short term memory as providing a mental work space that helps us to achieve our current goals and update our understanding of the world

• Alan Baddeley introduces his model of working memory

Central executive

• visuo-spatial

• episodic buffer

• phenological loop

• directs attention to and retrieves information from PL and VSS for integration in the episodic buffer

• Executive processes are used in planning and coordinating complex behavior:

  • Goal orientation

  • Focus attention

  • Control of social behaviour

  • Switching between tasks, updating memory, inhibition of distracting information

  • Planning and problem solving

  • Executive processes are governed by circuitry in the pre-frontal cortex, especially dorsa-lateral prefrontal cortex and the anterior cingulate cortex (ACC)

Phenological loop

• language

• with VSS are independent but interacting sub-systems, one for visual-spatial information and one for auditory-verbal information

• with VSS access and update language-based and visual representations in long term memory

• A mental workspace for manipulating auditory and verbal information.

• Digit-span backwards is considered a test of phonological/verbal working memory because you must actively manipulate the information in memory, rather than just maintain the sequence.

• Important in language development and verbal reasoning tasks.

Visuo-spatial sketchpad

• visual semantics

• with PL are independent but interacting sub-systems, one for visual-spatial information and one for auditory-verbal information

• with PL access and update language-based and visual representations in long term memory

• A temporary store for representations of visual and spatial information such as faces, objects written words and cognitive maps

• Enables the mental manipulation of visually and spatially represented information.

  • Mental rotation of objects

  • Visual and spatial mnemonics

  • Mental arithmetic

  • Cognitive maps” for navigation

Episodic buffer

• episodic long-term memory

• multi-modal memory traces formed in the episodic buffer and stored in episodic long term memory

Neural basis of working memory

• Executive processes are based within networks in the pre-frontal cortex

• The phonological loop (PL) is a left- hemisphere fronto-temporal lobe network.

• The visuo-spatial sketchpad (VSS) is a right occipital-parietal network.

• The episodic buffer integrates multi-modal information in an integrated ‘episodic trace’ within the parietal cortex (association cortex)