Study Notes on Short-Term Memory from Baddeley's Work

Definition of STM: - The functional capacity to retain small amounts of information over brief durations, usually ranging from 15 to 30 seconds without active rehearsal. It is essential for managing immediate actions and following complex multi-step instructions.
- Example Scenario: A teacher instructing children to "Put your books on the shelf, get your math folders, and line up at the door." This task requires the student to hold three distinct commands in a specific sequence while executing the first.

John Jacobs' Digit Span Test (1887): - Jacobs aimed to quantify the "mental capacity" of individuals by determining how many items could be successfully recalled in order.
- Key Concept: Digit Span - Definition: The maximum number of sequentially presented digits (or items) a person can recall correctly in at least $50\%$ of trials.
- George Miller (1956): - Introduced the "Magic Number $7 \pm 2$ ," suggesting that most adults have a capacity for approximately seven items, though modern research suggests this number may be lower (closer to $4$ ) when chunking is prevented.
- Standardized Assessments: The Digit Span remains a core subtest in the Wechsler Adult Intelligence Scale ( $WAIS$ ), used to assess cognitive processing and executive function.

Terminological Clarity:
- Short-Term Memory (STM): - A relatively passive storage component focused on the immediate retention of information without manipulation.
- Working Memory (WM): - A more dynamic, multi-component system that stores, manages, and manipulates information. It is critical for complex cognitive tasks such as mental arithmetic, reading comprehension, and logical reasoning.
Structural Differences: While STM is often viewed as a single, unitary store, WM is a workspace where information is processed using attention-based control.

Multicomponent Model (Baddeley & Hitch, 1974): - Replaced the concept of a single STM with a tripartite system (later expanded to four parts). It consists of:
1. The Central Executive: Coordinates attention and directs the flow of information.
2. The Phonological Loop: Handles auditory and verbal information.
3. The Visuo-spatial Sketchpad: Handles visual and spatial imagery.
4. The Episodic Buffer: (Added in 2000) Integrates information across domains into a single chronological representation.

Memory Span Variables:
- Item vs. Order: Recall depends not just on remembering the items but also their specific sequence.
- Linguistic Familiarity: Span is significantly reduced for items in a language the participant does not speak (e.g., an English speaker trying to recall digits in Finnish), as the lack of existing templates prevents efficient storage.

Chunking Definition: - The process of grouping individual pieces of information into larger, meaningful units (chunks) based on prior knowledge stored in Long-Term Memory (LTM).
Recall Strategy: For example, remembering the letters $I, B, M, F, B, I, C, I, A$ as nine separate units is difficult, but chunking them into $IBM$ , $FBI$ , and $CIA$ reduces the memory load to only three units, drastically increasing the effectiveness of recall.

R. Conrad's Findings (1964): - Demonstrated that even when stimuli are presented visually (e.g., letters on a screen), the brain tends to convert them into an acoustic code.
Confusability: Participants often mistook letters that sounded alike (e.g., mistaking $V$ for $B$ ) rather than letters that looked alike (e.g., mistaking $E$ for $F$ ).
Phonological Similarity Effect: Immediate serial recall is significantly worse for lists of words that sound similar (e.g., cat, mat, pat, hat) compared to words with distinct sounds (e.g., bus, clock, spoon, fish).

Phological Store ("Inner Ear"): - Holds speech-coded information for about $1.5$ to $2$ seconds before it decays.
Articulatory Rehearsal Process ("Inner Voice"): - An active process that refreshes the information in the phonological store through subvocal repetition, preventing decay.

The Two-Second Rule: People can generally remember as many words as they can say aloud in about two seconds.
Implication: Lists of long words (e.g., opportunity, university, aluminum) are harder to remember than lists of short words (e.g., dog, pen, hat) because long words take more time to rehearse, allowing the early items in the list to decay before they can be refreshed.

Definition: Requiring a participant to repeat a constant, irrelevant sound (like saying "the, the, the" or " $1, 2, 3$ ") while trying to memorize a list.
Consequences:
- It ties up the Articulatory Rehearsal Process.
- It eliminates the Word Length Effect because even short words cannot be rehearsed.
- It forces the participant to rely on visual coding rather than phonological coding.

Auditory Interference: STM performance drops when background speech is present, even if the participant is told to ignore it.
Changing State Hypothesis: Sounds that change frequently (like speech or melodies) disrupt order-based memory more than steady state sounds (like a continuous hum or white noise).

Primacy Effect: Better recall of items at the beginning of a list. This is attributed to more rehearsal time, which facilitates the transfer of these items into Long-Term Memory.
Recency Effect: Superior recall of the last few items in a list. This is attributed to these items still being present in the STM buffer. This effect is eliminated if there is a $30$ -second distraction task before recall.

Visual STM (The Cache): Stores what an object looks like (colors, shapes).
Spatial STM (The Scribe): Stores where objects are located in space.
Corsi Block Tapping Test: A common diagnostic tool where an examiner taps a sequence of blocks, and the participant must mimic the pattern. Average Corsi span is usually around $5$ blocks.

Dissociations: Evidence from brain lesions shows that different types of STM are handled by different brain regions.
- Patient KF: Suffered damage to the left parietal lobe; had a digit span of only $1$ or $2$ items but demonstrated normal long-term memory and normal visual STM.
- Patient PV: Shown to have a selective deficit in the phonological loop, making it impossible to learn new foreign language vocabulary, yet she could learn new associations between meaningful words.

STM is a high-speed, limited-capacity system vital for connecting perception to action.
Working Memory expands on STM by including attentional control and manipulation.
The distinction between verbal and visual-spatial subsystems is supported by both experimental data and clinical neuropsychology.