Working Memory:The Feature Model

Presented by: Umer Fareed

Outline Basic Concept of Working Memory

(WM) Three Component Model of WM Working Memory Capacity The Feature Model Feature Model Operation Simulations using Feature Model Pros and Cons of Feature Model Conclusion

Basic Concept of Working Memory A dedicated system that maintains and

stores information in the short term Supports human thought processes by

providing an interface between perception, long-term memory and action

Information decays quickly unless actively rehearsed

Sometimes referred to as short term memory

Proposed by Baddeley and Hitch Comprises a control (supervisory) system

and two storage (slave) systems; The Central Executive The Visuospatial Sketchpad The Phonological Loop

Three Component Model of WM

Working Memory Capacity Measures the extent to which a person can

control and sustain attention in face of interference and distraction

Ability to activate items in memory and to ignore or disregard interfering items

Correlate highly with many cognitive tasks including reading comprehension, spelling, vocabulary learning, writing and reasoning

Not about storage and processing but is about retention over a period in which there is distraction from stored information

Measured by a variety of tasks, commonly used are Reading Span and Operation Span

Reading span includes reading of a number of sentences and trying to recall the last word of each sentence in their correct order

In operation span, subject performs mathematical calculations and word reading and then asked to recall the words in order

Larger WM capacity means better ignorance to irrelevant or distracting information

Working Memory Capacity

The Feature Model Proposed by Nairne in 1988 Computational model of Serial Recall

guided by a set of “Primary Memory” (PM) cues of varying effectiveness in identifying the target item from a search set defined within “Secondary Memory” (SM)

Items are assumed to be represented as a set of features

A simplifying assumption is that only immediately adjacent items interfere

The Feature Model Items in PM and SM comprise sets of internally-

generated modality-independent (MI) and externally generated modality-dependent (MD) features organized as row vectors

MD features represent the conditions of presentation whereas MI features represent the nature of the item itself

For each partially degraded trace in PM, the subject tries to select an appropriate recall candidate by comparing degraded traces with intact traces in SM search set

Serial Position Function: Effect of change in MD features while keeping MI features constant

The Feature Model

The Feature Model

Item Presented Primary Memory

1 [ +1 -1 +1 +1, +1 -1 +1 -1] [ +1 -1 +1 +1, +1 -1 +1 -1] [ +1 0 0 +1, +1 0 +1 0]2 [ -1 -1 +1 -1, -1 -1 -1 -1] [ -1 -1 +1 -1, -1 -1 -1 -1] [ +1 0 0 +1, +1 0 +1 0] [ -1 0 +1 0, -1 -1 0 -1]3 [ +1 -1 -1 -1, +1 +1 -1 +1] [ +1 -1 +1 +1, +1 -1 +1 -1]

[+1 0 0 +1, +1 0 +1 0]

[ -1 0 +1 0, -1 -1 0 -1] [+1 -1 0 0, +1 0 -1 0]

4 [ -1 +1 -1 -1, -1 +1 +1 +1] [ -1 +1 -1 -1, -1 +1 +1 +1]

Example : Four Items are presented

Feature Model Operation Each to-be-remembered item is made

up of features Assume there are 20 MI features and 20

MD features, each of which is randomly set to a value of 1 or -1

These 40 features represent the first item presented, second item presented also contains 40 features

Item2 features overwrite Item1 features due to retroactive interference

Feature Model Operation If MI feature no 5 of item2 has the same value

as MI feature no 5 of item1, then original value of item1’s feature 5 is overwritten with a value of 0

Then item3 and item4 are presented, the final item presented is not followed by any external information but by rehearsal

At end of list presentation, primary memory contains trace of each item presented but these traces are degraded due to certain features being overwritten

Feature Model Operation Only the modality-independent features of

final item are overwritten whereas its modality dependent features remain intact

The subject then tries to match each primary item with an intact secondary memory trace

Beginning with first item, each PM item is compared with SM items in the comparison set, SM item with fewest mismatching features will be selected as a candidate for recall

Simulations using Feature Model The Serial Position Function Recall generally declines over serial positions

due to output interference If feature x of item n+1 is identical to feature x

of item n, then the value representing feature x of item n is lost and cannot be used as a recall cue

The recency effect seen in serial recall of auditory items arises because the MD features of the last list item are not overwritten whereas recency effect is not seen in visual presentation

Simulations using Feature Model The Suffix Effect Occurs whenever modality-dependent

features of the final item are overwritten Speech suffix significantly reduces serial

recall of auditory presented lists overwriting modality-dependent features of list of speech items

Visual suffixes have little or no effect on auditory list items

Simulations using Feature Model

Effects of Irrelevant Speech and Articulatory Suppression

Immediate serial recall of verbal material is reduced significantly if participants are exposed to irrelevant speech while studying the list items

If the target item is presented auditorily then irrelevant speech reduce serial recall performance under articulatory suppression

Feature adoption occurs when some of the MI features in PM are replace by features of word that is articulated

Simulations using Feature Model Effects of Irrelevant Speech,

Phonological Similarity and Word Length With visual presentation of list items, the

feature model predicts that there will be no effect of phonological similarity under conditions of irrelevant speech

Recall of visually presented material depends heavily on MI features, therefore, phonological similarity will produce no further damage to them

World length effect is eliminated by articulating suppression

Simulations using Feature Model

Suffix Effect and Articulatory Suppression Effect

Pros & Cons of Feature Model Can address effects at different serial

positions, including modality and suffix effects observable with auditory stimuli

Readily explains the absence of time-based word-length effects whereas working memory (Baddeley) has to predict that they will occur

Provides precise and unambiguous predictions as numbers used are easy to compare

Pros & Cons of Feature Model No role of time in the Feature

Model Only addresses serial recall not

free recall or recognition Recall of single list implemented in

the model whereas most experiments ask subjects to recall multiple lists

Conclusion Differs from other working memory

models as it does not use the concept of decay, rather interference degrades memory performance

Accounts for suffix effect remains even when subjects engage in articulatory suppression

Directly addresses modality effects

Questions

1. How has working memory capacity been found to affect dichotic listening?

2. Identify two shortcomings of Nairne’s feature model?

3. Identify two advantages that Nairne’s feature model enjoys over Baddeley’s working memory model?