Memory: Serial Position Effects and Working Memory Models
Memory: Serial Position Effects and Working Memory Models
Free Recall Task and the Serial Position Curve
Free Recall: A memory task where participants are presented with a list of words and asked to recall them in any order they wish after the list is over.
Example Word List: 1.) rock, 2.) pipe, 3.) dart, 4.) tree, 5.) film, 6.) cork, 7.) sofa, 8.) hand, 9.) book, 10.) belt, 11.) pond, 12.) cake, 13.) door, 14.) frog, 15.) flag, 16.) sand, 17.) wood, 18.) lamp, 19.) coat, 20.) drum.
Serial Position Effects: Refers to how the position of a word in a study list affects its probability of being recalled.
Primacy Effect
Definition: Better recall of words from the early portion of a list.
Consensus Explanation: This effect is attributed to Long-Term Memory (LTM).
Early items receive more extra rehearsal and attention from subjects, allowing them to be transferred into long-term memory.
Recency Effect
Definition: Better recall of words at the end of a list.
Traditional (Outdated) Explanation: Historically attributed to Short-Term Memory (STM).
The last few items on the list are still present in STM when the list ends.
In free recall, people typically recall these items earlier, directly from STM.
Challenging the Traditional View: The initial explanation was tested by delaying recall.
Hypothesis: If recency effects are due to STM, delaying recall (assuming no rehearsal of end-list items during the delay) should eliminate the recency effect.
Initial Findings: Experiments (e.g., with a 60s delay) indeed showed that a delay between the list presentation and the recall test eliminated the recency effect. This supported the idea that list items were no longer in STM.
Refined Understanding of the Recency Effect: Beyond STM
Evidence Against STM as Sole Cause: Numerous demonstrations of "long-term recency effects" suggest that STM is probably not the primary cause of all recency effects.
Example: Recalling what one had for breakfast (or lunch/dinner) for every day in a month shows a recency effect, even though these memories are clearly beyond STM capacity.
Alternate (Predominant) Hypothesis: Temporal Distinctiveness Account
Core Idea: Recency effects are not about whether information is still in STM, but rather that recent items are more temporally distinctive.
Distinctiveness Principle: Distinctive things are remembered better (e.g., one pink slide in a deck of black and white slides).
The last few items on any list are initially more distinctive and thus easier to recall (resulting in the recency effect).
As time passes, even the last few items become less distinct, blurring together with other past events, and the recency effect can diminish or disappear.
Analogy: Walking away from a fence line into the foreground makes the fence posts at the end appear less distinctive and "mash together." A delay after a list is analogous to moving into the foreground, causing the end items to lose their distinctiveness.
Long-Term Recency Effects and the Ratio Rule (Bjork & Whitten, 1974)
Experiment: Bjork & Whitten (1974) studied long-term recency by inserting long distractor periods (e.g., 30s) between words on the study list.
Format: Word [30s distractor] Word [30s distractor]…
They manipulated the retention interval (time between the last word and recall instructions) at the end of the list.
The "Ratio Rule": A formula describing when recency effects occur:
If the retention interval (time after the list and before the test) is longer than the delay between words during encoding, then no recency effect.
If the retention interval is shorter than the delay between words during encoding, then a recency effect will be observed.
Summary of Serial Position Effects Explanations
Primacy Effects: Due to extra rehearsal and attention given to the first few items, leading to LTM storage.
Recency Effects: Primarily due to the temporal distinctiveness of the last few items.
Modality Effect: If the list is auditory and the test is immediate, the recency effect can also be attributed to echoic memory (a sensory memory store for auditory information).
Working Memory: An Overview
Transition from STM: The "modal model" proposed a single STM system for processing any short-term information, primarily verbal. Working memory (WM) proposes a more sophisticated, multi-component system.
Defining Working Memory: WM is an active system responsible for temporarily holding and manipulating information during cognitive tasks like reasoning, comprehension, and learning.
Distinguishing WM from STM: Unlike the modal model's unitary STM, WM posits different subsystems for different types of information (e.g., verbal vs. visual-spatial).
Neuropsychological Evidence: Patients with greatly impaired digit span (a measure of verbal STM) showed no problems with verbal reasoning tasks or some visual STM tasks. Similarly, memory span tasks had little effect on verbal reasoning ability. This suggested multiple short-term storage systems, implying that STM itself might be modular.
Baddeley's Multicomponent Working Memory Model (Original)
Key Idea: Separate, domain-specific stores are coordinated by a Central Executive.
Components and Functions:
Central Executive (CE):
Acts as an attentional control system.
Responsible for reasoning tasks, allocating resources to other components, and supervising their activity.
Does not store information itself but manages the flow of information.
Phonological Loop (PL):
Recycles acoustic and verbal information.
"The mind's ear" - similar to the conceptualization of verbal STM in the modal model.
Involved in memory span tasks, understanding spoken language, and learning new vocabulary.
Visuo-spatial Sketchpad (VSS):
Handles visual and spatial information.
"The mind's eye" - involved in visual imagery tasks, spatial navigation, and mentally manipulating objects.
Demo Example (Grid Task):
Imagine a 4x4 grid. Place numbers according to spatial instructions (e.g., "Place a 1 in the second column of the second row, Place a 2 to the right of the 1, In square above 2, put a 3, To the right of 3 put a 4, Below a 4 put a 5, Below that put a 6, To the left of that put a 7). Answer: What number is above the 7? (Answer: 5).
Interaction with Long-Term Memory: The model implies interaction between the WM components and Long-Term Memory / Knowledge stores.
Alternative Model: Embedded-Processes Model (e.g., Cowan)
Key Idea: Working memory is not a system of distinct, separate storage buffers, but rather temporarily activated information within Long-Term Memory (LTM).
Focus of Attention: Approximately 3-4 chunks of information are accessible at once within the focus of attention.
Region of Direct Access: This is a subset of activated representations. Activated LTM representations that are currently in the focus of attention constitute working memory.
Emphasis: This model emphasizes attentional control over separate storage buffers, suggesting that WM capacity is more about the ability to control attention to activated LTM traces.