Memory Systems: Sensory Memory, Short-Term Memory, and Information Processing (copy)

Fundamentals of Memory and Memory Systems Overview

• Definition of Memory:

  • Memory is defined as the capacity to retain information over time.

  • Memory is fundamentally essential for human survival. Without memory, there is no capacity for learning ($\text{Memory} \rightarrow \text{Learning} \rightarrow \text{Survival}$).

  • Categorization—which allows organisms to identify and group stimuli for survival—is impossible without storing exemplar and category information in memory.

• System Plurality:

  • Research demonstrates that memory is not a single unified system.

  • Memory consists of multiple distinct systems, each possessing unique properties, structures, and operational rules.

• Taxonomy of Memory Systems:

  • Sensory Memory (subdivided into Iconic Sensory Memory and Echoic Sensory Memory).

  • Short-Term Memory (also referred to or used interchangeably with Working Memory).

  • Long-Term Memory.

Dimensions for Analyzing Memory Systems

• Every memory system is evaluated and distinguished across three core operational dimensions:

  • Coding:

  • Refers to the specific type or format of information that enters and is stored within a memory system.

  • Coding is frequently analyzed in terms of modality, referring to the physical or structural form of the sensory input (e.g., visual, auditory, tactile, or semantic modalities).

  • Duration:

  • Refers to the length of time information remains active and retrievable within a memory system before it decays, vanishes, or suffers interference.

  • Capacity:

  • Refers to the total quantitative volume or amount of information that a memory system can hold simultaneously.

Iconic Sensory Memory

• Definition and Coding:

  • Iconic sensory memory is the visual subtype of sensory memory.

  • Its coding is strictly modality-specific to visual sensory information.

• George Sperling's Experiments (1960s):

  • Whole Report Procedure:

  • Participants were flashed a grid of letters (e.g., a $3 \times 4$ matrix containing letters such as ASDX, PWHJ, SCVQ) on a screen for an extremely brief duration.

  • Participants were instructed to report as many letters from the grid as possible, either verbally or in writing.

  • Result: Participants consistently reported an average limit of approximately $5\,\text{letters}$.

  • Display Duration Modification:

  • Sperling increased the display exposure time to $500\,\text{ms}$ ($0.5\,\text{seconds}$).

  • Result: Participant recall performance did not improve beyond the initial limit of approximately $5\,\text{letters}$.

  • Partial Report Technique:

  • To test whether participants encoded more visual information than they could physically report before memory decay occurred, Sperling developed the partial report technique.

  • Procedure: Participants viewed the visual grid briefly. Immediately after the visual grid vanished from the screen, an auditory pitch cue was played:

    • High Tone: Instructed participants to report only the top row of letters (ASDX).

    • Medium Tone: Instructed participants to report only the middle row of letters (PWHJ).

    • Low Tone: Instructed participants to report only the bottom row of letters (SCVQ).

  • Result: Participants achieved near-perfect reporting accuracy for whichever specific row was cued by the auditory tone.

  • Inference: Because the auditory tone cue was delivered only after the visual stimulus had entirely vanished, participants must have encoded the complete visual grid into iconic sensory memory.

  • Mechanism of Limited Whole Report: The physical act of verbally or textually reporting letters takes time. During the time required to report the first few items, the remaining visual information rapidly decays out of iconic memory.

• Quantitative Parameters of Iconic Memory:

  • Duration: Extremely brief, lasting between $250\,\text{ms}$ and $300\,\text{ms}$ (approximately a quarter of a second).

  • Capacity: Large capacity, theoretically holding everything contained within the current visual field (e.g., briefly encoding every individual face across a massive, crowded lecture hall).

Echoic Sensory Memory

• Definition and Coding:

  • Echoic sensory memory is the auditory subtype of sensory memory.

  • Its coding is strictly modality-specific to auditory information.

• Auditory Partial Report Methodology:

  • To measure echoic memory parameters, researchers modified the partial report technique for the auditory modality.

  • Setup: Multiple distinct letter strings are audio-recorded and stereophonically mixed to sound as though they originate from distinct spatial locations in a room (e.g., four locations: front-left corner, front-right corner, back-left corner, and back-right corner).

  • Procedure: Participants listen to the simultaneous auditory letter streams. Immediately following presentation, a visual cue appears on a computer screen pointing to a specific spatial direction (e.g., top-right corner), signaling the participant to report the letter string that sounded as if it originated from that location.

• Experimental Testing of Operational Parameters:

  • Duration Testing via Interstimulus Interval (ISI):

  • Experimenters systematically manipulate the Interstimulus Interval (ISI)—the time delay between the end of the auditory sound presentation and the onset of the visual location cue.

  • At an ISI of $50\,\text{ms}$, recall accuracy is extremely high.

  • At an ISI of $500\,\text{ms}$ ($0.5\,\text{seconds}$), recall accuracy remains high.

  • At an ISI of $1000\,\text{ms}$ ($1.0\,\text{second}$), recall accuracy is sustained.

  • The ISI delay is incrementally widened until participant report accuracy degrades, marking the precise boundary of echoic storage duration.

  • Capacity Testing:

  • Experimenters systematically increase the length of the auditory letter sequences or musical tone lists presented until error rates indicate capacity limits.

• Quantitative Parameters of Echoic Memory:

  • Duration: Sustained significantly longer than iconic memory, lasting approximately $2\,\text{seconds}$ to $3\,\text{seconds}$.

  • Capacity: Holds approximately $5\,\text{tones}$ (e.g., $5\,\text{musical tones}$ or the auditory presentation of $5\,\text{letters}$).

Attentional Control and Sensory Memory Gating

• The Role of Attention:

  • Attention functions as the vital gating mechanism controlling whether information transitions from sensory memory into short-term memory.

  • Information present within sensory memory (iconic or echoic) that receives attention—whether conscious or subconscious—is actively transferred to short-term memory.

  • Unattended sensory information rapidly decays and is permanently lost.

• Demonstration of Selective Attention:

  • Focusing attention strictly on primary visual targets (e.g., reading text on a slide) causes unattended peripheral features in the visual environment (e.g., background furniture or the introduction of a new background object/figure named Nutly that was absent previously) to be completely ignored and omitted from short-term memory encoding.

Short-Term Memory Architecture and Coding

• Terminology and Functional Definition:

  • Short-Term Memory (STM) is a temporary memory store where information is maintained actively for brief durations.

  • In standard cognitive contexts, the terms Short-Term Memory and Working Memory are often used interchangeably.

• Coding Characteristics:

  • Unlike sensory memory systems, short-term memory is not modality-specific.

  • It encodes multiple distinct representation types simultaneously:

  • Visual Coding: Processing visual features, shapes, and spatial forms.

  • Auditory Coding: Processing acoustic inputs and sound structures.

  • Semantic Coding: Processing abstract meaning (semantic = having to do with meaning).

  • Translational Sequence Example: Seeing printed black line shapes on a display involves initial visual reception; translating those shapes via knowledge of the Latin alphabet produces letters; combining letters creates words; interpreting word concepts translates visual sensory input into semantic mental representations.

Short-Term Memory Capacity, Rehearsal, Chunking, and Interference

• Duration and Rehearsal:

  • The duration of short-term memory is not fixed.

  • Duration depends directly on rehearsal—the repetitive process executed to maintain items in memory.

  • Sub-vocal Rehearsal: The internal, silent vocalization and repetition of information within one's head to improve recall and prevent decay.

• Capacity and Variability:

  • Capacity is not fixed and varies based on three factors:

  1. The structural type of information being encoded.

  2. The amount of rehearsal completed.

  3. Individual differences across individual human capacities.

• Chunking Mechanism:

  • Definition: Chunking is the process of grouping individual visual, auditory, or semantic items in short-term memory into meaningful, integrated conceptual units ("chunks").

  • Function: Significantly expands the functional capacity of short-term memory.

  • Demonstration String: Consider the sequence MLBCWRURTA ($10\,\text{letters}$ total):

  • MLB: Grouped as Major League Baseball ($1\,\text{chunk}$).

  • CWRU: Grouped as Case Western Reserve University ($1\,\text{chunk}$).

  • RTA: Grouped as Rapid Transit Authority ($1\,\text{chunk}$).

  • Capacity Constraint: Even when utilizing chunking, short-term memory capacity remains constrained to approximately $4\,\text{chunks}$. Chunk sizes vary in letter length (e.g., CWRU has $4\,\text{letters}$ while MLB has $3\,\text{letters}$), but each functions as a single chunk if it forms a meaningful whole.

• Interference in Short-Term Memory:

  • Definition: Interference occurs when targeted information in memory cannot be accessed or retrieved at a specific time because it has been displaced by competing incoming information.

  • Mechanism Example: Assume Person A is assigned to memorize numeric set 347890 and Person B is assigned to memorize numeric set 156478:

  • While Person A attempts sub-vocal rehearsal of 347890, Person B begins vocalizing 156478 out loud.

  • Person B's spoken output generates an auditory echoic trace that interferes with Person A's sub-vocal rehearsal loop, displacing 347890 from Person A's short-term memory.

  • Impact on Memory Transfer: Interference directly tampers with and disrupts the transfer of information from short-term memory into long-term memory.

The Serial Position Effect: Primacy and Recency Phenomena

• Serial Position Effect Definition:

  • The specific sequential order or position in which an item occurs within a task or list directly influences its retrieval success from memory.

  • Items positioned at the beginning and at the end of a sequence are recalled significantly better than items located in the middle.

• List Demonstration Analysis:

  • When presented with a sequential list of words—such as Table, Candle, Maple, Subway, Pencil, Coffee, Softball, Curtain, Player, Kitten, Towel, Doorknob:

  • Early items (Table, Candle) exhibit high recall rates.

  • Terminal items (Towel, Doorknob) exhibit high recall rates.

  • Intermediate items (Maple, Subway, Pencil, Coffee, Softball, Curtain, Player, Kitten) show significant recall degradation and become forgotten.

• Primacy Effect:

  • Definition: The specific component of the serial position effect describing superior recall performance for items located at the beginning of a list or task.

  • Mechanism: Early items receive a disproportionate amount of extra sub-vocal rehearsal (e.g., repeating "table… table, candle… table, candle, maple…"). This cumulative extra rehearsal facilitates successful transfer into long-term memory.

  • Experimental Elimination: Experimenters can eliminate the primacy effect by presenting list items at an extremely rapid pace (e.g., rapid-fire reading of Table, Candle, Maple, Subway). Rapid presentation deprives participants of the time necessary to execute extra rehearsal.

• Recency Effect:

  • Definition: The specific component of the serial position effect describing superior recall performance for items located at the end of a list or task.

  • Mechanism: Terminal items remain directly accessible because they are still present in active short-term memory or temporary sensory memory buffers (such as echoic memory's $2\,\text{seconds}$ to $3\,\text{seconds}$ trace).

  • Experimental Elimination: Experimenters can eliminate the recency effect by introducing an immediate distractor task immediately following the presentation of the final item (e.g., instructing participants to