working memory: the feature model presented by: umer fareed
TRANSCRIPT
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
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