Sensory, short-term and working memory - summary of chapter 4 of Cognitive Psychology by Gilhooly, K & Lyddy, F, M

Cognitive Psychology 
Chapter 4
Sensory, short-term and working memory

Memory

• Encoding: the function by which information is coded in a form that allows it to be stored in memory.
• Storage: the function by which information is retained in memory
• Retrieval: the function by which information is recollected as needed.

Distinction between:

• Short-term memory (STM): the store where information is temporarily held in an accessible state.
• Long-term memory (LTM): the system where information is held for longer periods, and can be accessed when needed.

Recollection: the act of recalling something to mind. Used by LTM
STM allows a small amount of information to be held in mind, so that it is immediately accessible and can be used.

Working memory (WM) refers to memory that allows us to manipulate active information. There is considerable overlap between the terms short-term memory and working memory.

Before a piece of information enters short-term memory, its sensory aspects are stored temporarily in a very short-lived store called sensory memory.
Sensory memory: a temporary sensory register that allows input from the sensory modalities to be prolonged.

Sensory memory

The sensor memory stores allow input from the sensory modalities (vision, hearing, etc.) to be prolonged briefly in order for us to process relevant aspects of that input.
It is essentially a temporary sensory register, of large capacity, by which fades rapidly.
Models of sensory memory assume a number of modality-specific sub-stores dealing with different types of input.

Sensory memory consists of a number of modality-specific stores.

• Iconic memory: visual stimuli
• Echoic memory: auditory stimuli
• Haptic sensory memory: touch-related stimuli.
• The sensory store prolongs sensory information so that we an attend to important parts of it. Aspects that are not attended to fade away.

Iconic memory

Iconic store is the sensory memory store for visual stimuli.
The spatial advantage disappears after a delay of about half a second.
There is a brief memory of a visual image, which is potentially very large in capacity but which rapidly fades away. Thus iconic memory.

Iconic memory allows visual input to be prolonged, which means that our visual experience is not an exact reflection of reality.
This allows us to see a series of still images as moving picture sequences in motion pictures and animation.

Echoic memory

Echoic memory is sensory memory for heard information.
A large initial memory of auditory information which decayed rapidly.
The echoic store provides an acoustic register, allowing auditory presented information to be prolonged so that some aspects of the input can be retained later.

Shadowing: a technique that involves repeating back an auditory presented message.

An auditory store that prolongs auditory stimuli, and provides and estimation of echoic persistence.

Information held in the sensory register is not yet in a form that the cognitive system can effectively utilize and manipulate. For this, further processing and transfer to short-term memory is needed.

Sensory memory is fragile and can easily be disrupted before stimuli can be transferred into short-term memory.

• Backward masking procedures involve the presentation of a ‘masking’ stimulus immediately after the target stimulus.
  Masking: reduced perception of a visual stimulus when another stimulus is presented in spatial or temporal proximity to it.
  Stimulus onset asynchrony: the time between the onset of a stimulus and the presentation of a mask.

Two stages to sensory memory in each of the modalities.

• A short, per-perceptual phase lasting about 250 milliseconds
• Longer, lasting several seconds and involving more substantial processing and access to memory.

Haptic memory

Sensory memory provides a temporary register that is rich in sensory detail, such memory is short-lived and cannot be manipulated.
In order for effective processing to occur, information must be held in short-term memory.

Short-term memory

Holds information in consciousness. It provides temporary storage of active information.
STM has limited capacity and information can be lost from it relatively easily.
It allows us to complete the many daily tasks that involve active use of information.
It is not limited to verbal information.
Much of the information that we process in STM is not retained, and is quickly purged from STM, allowing our attention to move on to the next task.

The modal model
Three memory stores.

• Long-term store
• Short-term store
• Sensory register

Memory is
First registered in the sensory store. Salient information is transferred to STM.
A number of control processes are supported by STM and the type of processing carried out will determine whether information will be stored in LTM.

• Rehearsal: recycling of information
• Maintenance rehearsal: retains information in STM. Repeating it to yourself to keep the information refreshed in memory
• Elaborate rehearsal: organizes the information so that it can be integrated into LTM

Information is lost from STM through

• Decay: a time-based limitation
• Displacement: information coming into STM causes information already held there to be lost.

Digit span: the number of digits that can be held in memory and is used as measure of STM.

7+/- 2

Chunking: a strategy to improve memory by grouping smaller units together into a larger unit or ‘chunk’.
Increases the capacity of STM.
Information from LTM can be used to facilitate chunking.

Serial position curve: used to plot of a word list such that performance is examined as a function of a word’s position in a list.

The recency effect: the tendency, given a list of items to remember, to recall those from the end of the list more readily than items from the middle.
Items held in STM.

Primancy effect: enhanced recall of items at the start of a list compared to those in the middle.
Items that have already been transferred to LTM.

The negative recency effect:; reflects poorer memory for list-end items compared to items from earlier input positions, in multi-list recall tasks.

Double dissociation of function: contrasting patterns of deficit in two patients or patient groups which provides evidence for functionally independent systems.

The modal model is incomplete.

Working memory: memory that allows us to make plans and to keep track of goals.
Not entirely distinct from short-term memory. It includes storage and processing components.

Working memory

Different sub-systems must underlie tasks such as digit span and word list learning.

Working memory
The ‘workbench’ of human cognition.
The collection of mental processes that permit information to be held temporarily in a accessible state, in the service of some mental task.

• The focus of attention
• Information that is temporarily activated in the system, including information about our current goals and plans.
• A sensory-specific multi-component storage system for short-term storage and processing information.

Accounts of working memory also vary in how they consider the relationship between working memory and long-term memory.

Cowan’s embedded processes model:
WM as consisting of a capacity-limited focus of attention and a temporarily activated subset of long-term memory.
This account places emphasis on the interaction of attention and memory and considers WM in the context of LTM.
Three components contribute to working memory:

• Temporarily activated information that is not yet accessible to conscious awareness.
• Memory within the focus of attention
• Information stored in LTM, which is currently inactive but could be retrieved/ activated if relevant to the task.

These key components contribute to WM as embedded processes, with the current focus of attention being a subset of active memory and active memory presented as a subset of LTM.
Information is lost from WM trough processes of:

• Decay
• Displacement

The focus of attention is capacity limited and information can be easily displaced from it, while the activated memory is time-limited, and information can decay if not rehearsed.
The nature of the representation may vary in WM but it does so within a single structure that has fixed properties. The distinctness and non-interchangeability of phonetic and spatial information occurs because different types of features are being activated, not because of distinctly different storage modules’.

Multiple component models of WM.
WM can be fractionated into component parts.
The principal function of WM is the coordination of resources and focuses on identifying and examining the nature of the structures that carry out this function.
WM consists of both storage and processing components and might be defined as ‘the simultaneous processing and storage of information’.
Mulitcomponent, limited-capacity system responsible for retaining as well as transforming fragile representations.
A brain system that provides temporary storage and manipulation of the information necessary for such complex tasks as language comprehension, learning and reasoning.

Baddeley’s working memory model

The essence of the concept of working memory lies in its implication that memory processes play an important role in non-memory tasks.
WM is not just a store for maintaining information in consciousness, it plays an integral role in ongoing or ‘online’ cognitive processing.

The core of the WM system is a limited capacity work space. Which can be divide between storage and control processing demands.

Four main components to working memory:

• The central executive
  Proposed to control and coordinate the activity of the other components.
  Provides the attentional control of working memory.
  Modality-free. It can deal with input from any modality.
  Similar to attention.
  Served by the visou-spatial sketchpad and the phonological loop.
• The visuo-spatial sketchpad
  Proposed for the temporary storage and manipulation of visual and spatial information. (these are modality-specific)
• The phonological loop
  Proposed for temporary storage and manipulation of sound or phonological information. It comprises a short-term phonological store for auditory memory traces and an articulatory rehearsal component to reactivate memory traces.
• The episodic buffer
  Proposed for the temporary storage of information integrated from the phonological loop, the visuo-spatial sketchpad and long-term memory into single structures or episodes.

The phonological loop

Specialized for speech-based information.
Implicated in tasks involving verbal materials.
Also involves sub-vocal articulation.

• The inner voice

The articulartory loop has limited capacity, restricted by temporal duration, and it holds as many verbal items as a person can say in about 2 seconds.

Anarthria: a disorder affecting the motor function underlying speech.

The phonological loop has two sub-components

• A phonological store.
  Holds speech-based information for a period of about 2 to 3 seconds.
• An articulatory control processes
  Which allows the maintenance of information in the store and converts visual information to a speech-based form.

The articulatory control process uses sub-vocal rehearsal to fulfill these functions, a process that can be linkened to inner speech.
Auditory presentation of phonological information gains direct access to the loop.
Visually presented information gains access via sub-vocal articulation by the articulatory control process.

Evidence for the phonological loop:

• The word length effect
  The advantage found for recall of lists of short words compared to longer words. The duration it takes to articulate the word is the crucial factor, not the number of syllables.
• The effects of articulatory suppression
  The ability to rehearse sub-vocally can be disrupted if we require a participant to rehearse a string that is irrelevant to the current task.
• The irrelevant speech effect
  Recall of visually presented verbal material is poorer when irrelevant speech is presented during learning. The effect is limited to speech sounds and one does not need to understand what is being said in order for the speech to disrupt processing.
• The phonological similarity effect
  Recall is poorer for an ordered list of verbal items when the items sound alike, relative to performance on lists of items that do not sound alike. Items that are similar in meaning do not show this effect. But, when information from LTM comes into play, the phonological similarity effect may be diminished or absent.

Functions of the phonological loop

• Plays a key role in the acquisition of new vocabulary
• Involved in the temporary storage of part solutions during mental arithmetic, while the central executive performs the more demanding manipulations.

The visuo-spatial sketchpad

The ability to manipulate visual images relies on visual short-term memory and this type of memory is provided by a separate component. The visuo-spatial sketchpad. (VSSP)
Specialized for dealing with visual and spatial information.
It has limited capacity, of about three or four objects.

Two components. Separate, but strongly interconnected.

• A visual cache
  The component within working memory that stores visual information.
  Stores information relating to visual form.
  Passive.
• Inner scribe
  Allows spatial processing.
  Maintains information in the store through a type of rehearsal process.
  LTM involvement is central to VSSP functioning.

Data from dual-task performance shows selective interference of visual and spatial working memory tasks.
Further evidence supporting the distinction between the visual cache and the inner scribe comes from neuropsychological case studies.

The central executive

The workhorse and mastermind of human cognition.
The most important component of working memory.
A general processing mechanism that handled the more complex types of short-term memory task that were not delegated to the PL or the VSSP.
A supervisory system which plays a key role in controlling and regulating working memory function.
It:

• Coordinates the activities of the PL or the VSSP
• Focuses
• Switches attention.

Involved in controlling active information, but not in the storage per se.
It is useful to separate the storage and control functions of working memory.
It is likely that the central executive consists of a number of subsystems, which have yet to be identified.

Two types of cognitive control reflecting the distinction between automatic and controlled processes

• The automatic system of control allows us to perform routine and well-practiced actions trough the selection of learned habits and schema's without the need for deliberate cognitive control.
  Our actions are directed by relevant schemas, activated by triggers in the environment.
• Attentional control mechanism (the supervisory activating system or SAS)
  Which can interrupt automatic processing, select an alternative schema and allow attention to be directed towards a goal.

These two qualitatively distinct control systems allow three levels of functioning:

• A fully automatic mode for routine actions
• An intermediate, partially automatic mode which allows attentional control of actions
• The deliberate control of action for non-habitual or novel tasks

Evidence for two separate control systems (one governing performance or routine actions and the other allowing control of non-routine action)

• Studies of patients with frontal lobe damage.
  Capture errors: failure to override a routine set of actions. (stroop test)
  Dysexecutive syndrome: a range of deficits reflecting problems with executive function and control. Often associated with injury to the frontal areas of the brain.
  Perseveration: the inappropriate repetition of an action.

The central executive also allows us to maintain focus and to keep our attention on the task at hand.

Utilization behavior: dysfunctional automatic reaching for and use of objects in the environment.

The episodic buffer

Working memory can make use of additional storage capacity.
Some verbal learning tasks involve a larger storage capacity than is supported by data on the phonological loop.
The episodic buffer can be accessed by the central executive or by the slave systems, which links to LTM.
A crucial feature of the capacity of working memory to act as a global workspace that is accessed by conscious awareness.
A temporary storage structure of limited capacity that is controlled by the central executive and allows information from different sources to be integrated, essentially providing a means of interface between the modality-specific systems of WM and LTM.
It is the storage component of the central executive.
Episodic in the sense that it holds episodes whereby information is integrated across space and potentially extended across time. It is assume to be a temporary store and to play an important role in feeding information into and retrieving information from episodic LTM.