PSYC327: Short-Term Memory

Short-Term Memory (STM)

processes that maintain info. for very short periods (< 1 min).

- e.g., digit span task

- No manipulation or observation going on

Working Memory (WM):

processes that maintain and manipulate info. to achieve an immediate goal

- e.g., 55+12+9 = 76

- Manipulation and active

Working Memory Task

retain & manipulate task

Short-Term Memory & Brain Damage: Case KF

- He was able to remember which tasks/clients he had worked with just before his illness, and had no problem learning new tasks and remembering new clients.

- Difficulty repeating digits (digit span of 1)

Case KF: Key Point

Short-term memory not a "gateway" to long-term memory (loss does not affect long-term learning)

Verbal Short-Term Memory: Brain Regions - Experiment w Stroke Survivors

Damage in left posterior temporal, inferior parietal lobe: region associated with poor digit span scores, large group of stroke survivors

Located in the junction/intermediate area of the ventral and dorsal language streams

Damage to area = difficulty with verbal short-term memory

Verbal Short-Term Memory: Brain Regions - fMRI

Found a small amount of activity in the left posterior temporal, inferior parietal lobe and Broca's area

Verbal Short-Term Memory: Brain Regions - MEG Study

The activity was different between the fMRI (Broca's area) & MEG study because during the fMRI delay had a rehearsal of the digits

- more activity in frontal cortex

Visuospatial Short-Term Memory: Brain Regions

- right hemisphere damage > left (spatial memory favoured by right hemisphere)

- More likely to have a thinning in the posterior (same structures that processes space)

Corsi Blocks Task

- Present the pp with a series of blocks and examiner points to a random sequence of blocks

- Participants has to point to the blocks in the same order

- Measures STM & visuospatial aspects

- No verbal information is tested

Brain Region Damage Associated with Poor Corsi Block Task Performace

Found that damage that lead to poor performance had the dorsal stream involved and it was right lateralised

Working Memory: Baddeley's Model

- two "passive" stores = one for verbal and the other for visuospatial information

- a control centre = the Central Executive

○ Central Executive can manipulate the stored information to solve problems

○ Can operate to extent how much time something is stored

§ Happens due to actively using frontal systems

Baddeley's Model: Verbal STM

Left temporo-parietal; Phonological store

Baddeley's Model: Visuospatial STM

Right parietal

Baddeley's Model: The Central Executive

- Central Executive can manipulate the stored information to solve problems

- Can operate to extent how much time something is stored due to actively using frontal systems

- • Refreshes, reorganises & rehearses info in "slave" storage systems

- Can manipulate that information on-line

- Requires mental effort and sustained attention

- Phonological loop = rehearsal

Location of the Central Executive

prefrontal cortex/frontal lobe

The Role of Prefrontal Cortex

Prefrontal areas especially active during rehearsal

The Role of Prefrontal Cortex: fMRI Studies

- Participants heard strings of words or letters, had to repeat back after an 8-12s delay

- Left prefrontal cortex activated only during delay (while person is rehearsing)

- Supports idea of rehearsal "loop"

The Role of Prefrontal Cortex: Stroke Survivors

- Poor scores on corsi block tapping task were associated with damage in the left posterior temporal and inferior parietal cortex

- Manipulating to reversal = more prefrontal areas engaged

- Supports the Central Executive being located in the prefrontal cortex

The Role of Prefrontal Cortex: fMRI & Visuospatial Information

- condition one: remember whether they've seen the image

- condition two: remember whether they've seen the image but image is rotated so must mentally rotate

- Regions more activated for manipulation task: activates parietal cortex AND prefrontal areas, especially on the right

Number of Central Executives

there are multiple central executives because there are two different sides of the brain (visuospatial and verbal)

Working Memory: Cowan's Model

- Short-term memory is not a separate system (or set of systems)

- Rather, STM involves temporarily activating & maintaining knowledge elements from LTM

- The brain structures activated depend upon the material

Cowan's Model: LTM

Network of knowledge already acquired

Cowan's Model: WM

Activation of specific stimuli

Cowan's Model: Complex WM

Focus of attention on 3-4 elements activated to manipulating the information