Short-Term Memory Notes

Short-Term Memory and Working Memory

Memory is the process of retaining, retrieving, and using information about stimuli, images, events, ideas, and skills after the original information is no longer present.
Memory is active whenever a past experience affects how you think or behave now or in the future.
Memory connects the past to the present and potentially the future.

Types of Memory

Sensory Memory: Brief persistence of perception after a stimulus is presented (e.g., seeing a face illuminated by a flash).
Short-Term Memory/Working Memory: Information held for brief periods (10-15 seconds), unless repeated.
Long-Term Memory: Storing information for long periods (minutes to a lifetime).
- Episodic Memory: Long-term memories of experiences (e.g., a picnic).
- Procedural Memory: Ability to perform tasks involving muscle coordination (e.g., riding a bicycle)
- Semantic Memory: Memory of facts (e.g. address, birthday).

Modal Model of Memory

Models of how the mind works are central to research in cognitive psychology.
Atkinson and Shiffrin (1968) proposed the modal model of memory, which includes three types of memory:
1. Sensory Memory: Initial stage holding incoming information for fractions of a second.
2. Short-Term Memory (STM): Limited capacity, holding 5-7 items for 15-20 seconds.
3. Long-Term Memory (LTM): Limitless capacity, holding large amounts of information for years.
These three types are called structural features of the model.
Control Processes: Dynamic processes associated with structural features, regulated by the person (e.g., rehearsal).
Rehearsal: Repeating a stimulus to hold it in mind.
Other control processes include strategies to make stimuli memorable (e.g., relating digits to a familiar date) and attention strategies.

Illustration of Structural Features and Control Processes

Information enters sensory memory.
Selective attention focuses on specific information, which enters short-term memory.
Rehearsal keeps the information in short-term memory.
Encoding: Storing the information in long-term memory.
Retrieval: Remembering information stored in long-term memory, returning it to STM.
Components of memory interact; information is transferred between STM and LTM.

Sensory Memory

Sensory memory retains the effects of sensory stimulation for brief periods.
Persistence of Vision: Continued perception of a visual stimulus even after it is no longer present.
Example: The trail of a moving sparkler.
Persistence lasts for a fraction of a second.

Sperling's Experiment

Sperling (1960) investigated how much information people can take in from briefly presented stimuli.
Letters were flashed on a screen for $50$ milliseconds.
Whole Report Method: Participants report as many letters as possible from the entire display.
- Participants reported an average of $4.5$ out of $12$ letters ( $37.5$ %).
Participants reported seeing all letters, but perception faded rapidly.
Partial Report Method: Participants report letters in a single row indicated by a tone after the flash.
- High tone: top row
- Medium tone: middle row
- Low tone: bottom row
- Participants correctly reported an average of $3.3$ of the $4$ letters in that row (approximately $82$ %).
Sperling concluded participants had access to $82$ % of the letters but faded rapidly during reporting.

Delayed Partial Report Method

Cue tone presented after a delay.
When the cue tones were delayed for one second, participants could report only slightly more than one letter in a row.
Sensory memory fades quickly.
After $0.1$ seconds, about $60$ % of the letters were available.
After $0.3$ seconds, this dropped to $50$ %.
Iconic Memory: Brief sensory memory for visual stimuli, corresponding to the sensory memory stage of the modal model.
Echoic Memory: Persistence of sound, lasting for a few seconds (Darwin, Turvey, & Crowder, 1972).
Sensory memory registers large amounts of information but retains it only briefly.

Short-Term Memory (STM)

STM stores small amounts of information for a brief period.
Information you are currently thinking about is in short-term memory.
STM is essential for our mental life, acting as our window to the present.
It allows awareness of current events, transfer from LTM and communication.

Duration of Short-Term Memory

STM lasts for only $15$ to $20$ seconds or less.
Brown (1958) and Peterson and Peterson (1959) demonstrated this using a recall method.
Participants recalled about $80$ % of three-letter groups after counting for three seconds.
Only $12$ % were remembered after counting for $18$ seconds.
It was initially thought that memory decayed during the $18$ -second delay.

Interference

Keppel and Underwood (1962) found memory was high on the first trial, even after an $18$ -second delay, suggesting that decay was not the primary cause of forgetting.
Proactive Interference: Previous information interferes with learning new information.
Retroactive Interference: New learning interferes with remembering old learning.
Interference happens constantly as one event follows the next and we pay attention to one thing after another.
The effective duration of STM, when rehearsal is prevented, is about $15$ to $20$ seconds or less

Capacity of Short-Term Memory

STM has a limit on how much information can be held.
Estimates range from four to nine items.
Digit Span: The number of digits a person can remember is one measure of STM capacity.

Chunking

Chunking enables the STM system to deal with large amounts of information.
By arranging words to form a meaningful sentence your memory span will likely increase
STM refers to a structural feature of memory, while chunking is a control process.
People may store more items using effective control processes, not necessarily a larger STM capacity.
Ericsson et al. (1980) showed how a college student with average memory ability was able to achieve amazing feats of memory by repeating digits to him.
After extensive training (230 one-hour sessions), he was able to repeat sequences of up to 79 digits without error.
SF used chunking to recode the digits into larger units that formed meaningful sentences.
The capacity limit of STM also depends on the compressibility of the to-be-remembered materials.
Mathy and Feldman systematically manipulated the compressibility of number sequences.
After compression, most participants could only remember three to four distinct chunks.
The true limit of STM capacity is more likely to be four than seven.

Change Detection

Change detection tasks use visual items that cannot be verbalized.
This procedure may be better suited to assess STM storage capacity independent from any control processes and/or LTM involvement.
Individual differences in storage capacity were also observed in this and other experiments using similar tasks
Individuals with a larger storage capacity also performed better on complex cognitive tasks.
visual short-term memory capacity somehow plays a central role in higher cognitive functioning.
Storage and selective processing and attention control relate to intellectual aptitudes (Engle, 2002; Unsworth, Fukuda, Awh, & Vogel, 2014).

Amount of Information vs. Number of Items

Researchers suggest describing memory capacity in terms of "amount of information" rather than "number of items."
Amount of information is defined as the visual features or details of the object that are stored in memory (Alvarez & Cavanagh, 2004).
Alvarez and Cavanagh (2004) used complex objects like shaded cubes in a change detection procedure.

Working Memory

Baddeley and Hitch (1974) defined working memory as "a limited-capacity system for temporary storage and manipulation of information for complex tasks such as comprehension, learning and reasoning."
Working memory involves the manipulation of information during complex cognition.
Example: Understanding a conversation while remembering previous sentences.
Working memory is important for language processing, including second language acquisition.
Working memory is also important for language

Components of Working Memory

Baddeley and Hitch (1974) proposed that working memory consists of three components: the phonological loop, the visuospatial sketch pad, and the central executive.
The notion of a single system is replaced with one comprising at least three separable but interacting subsystems
The assumption of a series of successive stages of information processing is substituted by a model that is capable of parallel processing across the different subsystems.
Phonological Loop: Holds verbal and auditory information.
- Phonological Store: Limited capacity, holds information for a few seconds.
- Articulatory Rehearsal Process: Rehearsal to keep items in the phonological store from decaying.
Visuospatial Sketch Pad: Holds visual and spatial information (e.g., forming a picture in your mind or doing tasks like solving puzzle).
Central Executive: Coordinates activity of the phonological loop and visuospatial sketch pad by focusing attention on specific parts of a task and dividing attention between different tasks.

Central Executive as Traffic Controller

The central executive is the "traffic controller" of the working memory system.
Coordinates phonological loop and sketchpad.
Helps ignore distractions and focus attention.

Assessing Working Memory Capacity

Tests involve remembering a word or digit while performing another attention-demanding task.
Reading Span Task: Participants read sentences and recall unrelated words.
Operation Span Task: Participants perform arithmetic operations and recall words.
These tasks are not short-term memory capacity with something important to higher-order cognition
Engle (2002) suggested that tasks reflect executive attention and possibly fluid intelligence.
Working memory capacity reflects a general limitation on attentional capacity rather than storage capacity.

Evidence for the Phonological Loop

The phonological similarity effect and also the word length effect and articulatory suppression will be described.
Phonological Similarity Effect: Confusion of letters or words that sound similar.
Word Length Effect: Memory is better for short words than long words.
Articulatory Suppression: Repeating an irrelevant sound reduces memory because speaking interferes with rehearsal.

Visuospatial Sketch Pad

Handles visual and spatial information, involving visual imagery.
Recalling Visual Patterns: Requires visual coding.
Holding a Spatial Stimulus in Mind: Operation can be disrupted by interference.

Central Executive as Attention Controller

The central executive is responsible for focusing attention on a specific task and dividing attention between two tasks
Controls phonological loop and visuospatial sketch pad processes

Vogel et al. (2005) Experiment

Divided participants into high-capacity and low-capacity groups based on working memory performance.
Recorded so-called event-related potentials (ERPs) from which someone's "filter efficiency" could be derived.
Individual differences in working memory capacity variations are not about the absolute size of storage space but about selectively keeping relevant information in and irrelevant information out.

The Episodic Buffer

Research has shown that working memory can hold more than would be expected based on just the phonological loop or visuospatial sketch pad.
The episodic buffer represents a way of increasing storage capacity and communicating with LTM.
Baddeley proposed the episodic buffer as an additional component of working memory.
The episodic buffer can store, link and integrate different kinds of information from all the subcomponents of working memory and from LTM.

Cowan's Embedded Processes Model

The embedded processes model by Cowan (1988, 1999, 2005) suggests that working memory is organized in two embedded levels.
The first level consists of a temporarily activated portion of information that is stored in long-term memory
The second level of Cowan's model consists of a subset of the activated representations, namely those that fall within the focus of attention

Working Memory and the Brain

Cognitive psychologists use various methods to determine the connection between cognitive functioning and the brain.
1. Analysis of behaviour after brain damage, either human or animal.
2. Recording from single neurons in animals.
3. Measuring activity of the human brain.
4. Recording electrical signals from the human brain.
Working memory tasks involve a delay during which information needs to be kept accessible.

Effect of Damage to the Prefrontal Cortex

Damage to the frontal lobe causes problems in controlling attention.
Early research used the delayed-response task with monkeys. The monkey sees a food reward in one of two food dishes.
If their prefrontal cortex is removed, their performance drops to chance level

Prefrontal Neurons that Fire when Holding Information

Funahashi, Bruce and Goldman-Rakic (1989) conducted an experiment in which they recorded from neurons in a monkey's prefrontal cortex while the monkey carried out a delayed-response task.
The key result of this experiment was that there were neurons that responded only when the square was flashed in a particular location and that these neurons continued responding during the delay.

MRI Research

Sustained activity in prefrontal areas is necessary to maintain abstract and coarse representations of what was presented in working memory along with rehearsal
The actual detailed content of working memory is stored somewhere else in the brain.
Christophel et al. (2017) suggest that the representations in the prefrontal cortex may be in such format that they can guide an upcoming behavioural response.
To see whether working memory also involves activation of early visual areas, Harrison and Tong (2009) did an experiment in which they flashed two oriented sample gratings.