Chapter 6: Long-Term Memory Structure

Anatomic Dissociation

Evidence that two different tasks are supported by different parts of the brain.

Evidence of Explicit vs. Implicit Memory: H.M. (Henry Molaison)

Had much of his medial temporal lobe removed to relieve epilepsy. Left him with anterograde amnesia— couldn’t store new memories. But he could learn new motor skills. Showed evidence of two long term-memory systems, implicit and explicit.

What Amnesia helped us understand

It’s not just that there is memory and there are motor skills: perceptual stuff can be preserved. People start to think of amnesia as memory minus some process; this missing process impairs most memory tasks, but certain tasks don’t depend on the missing process, so the tasks are learned.

Explicit Memory

A type of memory retrieval that is conscious, usually measured by verbal report. Explicit retrieval would typically be supported by declarative memory. Declarative refers to the memory system, and explicit refers to the type of memory test. Conscious recollection of facts, experiences, and concepts. Tested directly via recall or recognition tasks where participants are aware they are remembering.

Associated with the Hippocampus.

Explicit Memory: Episodic Memory

Autobiographical memory for personal experiences. Memories associated with a particular time and place, with a this-happened-to-me feeling. Involves consciousness, past events, encoding is rapid and automatic, retrieval process is required, retrieval depends on cues, it is fail-able and reconstructive. Subsystem of Explicit memory.

Explicit Memory: Semantic Memory

General factual knowledge about the world without personal context. Memories that cover world knowledge. All semantic memory must start as episodic. Subsystem of Explicit memory.

Implicit Memory

A type of memory retrieval that is unconscious and is measured not by verbal report but via some performance measure. The experimenter can tell that the participant has learned by how the participant performs some task.

Implicit Memory: Motor Skill Learning

The knowledge of how to complete a set of motor actions, without necessarily even realizing that we are using memory. Motor skill memory is knowledge of how to execute physical actions without consciously recalling the steps or rules involved. It is divided into two primary types, sequencing skills and adaptation skill.

Associated with Basal Ganglia.

Sequencing Skill

Sequence of movements to be executed quickly and accurately. For example, competitive cup stacking.

Adaptation Skills

A type of motor skill learning in which a new motor response is learned to a visual stimulus, for example using a computer mouse. The way that the stimulus and response go together is systematic, which contrasts with arbitrary visual-motor associations.

Implicit Memory: Repetition Priming

Effect in which performance of a task is biased by one’s having seen the same words or pictures sometime earlier.

Demonstrations of Repetition Priming: Gollin incomplete figures, stem completion (i.e. Rea___), fragment completion, and lexical decision tasks.

Associated with the Visual Cortex.

Implicit Memory: Conditioning

Conditioning involves learning associations between environmental stimuli and automatic responses, divided into two types based on the nature of the conditioned response, classical conditioning and emotional conditioning.

Skeletal (Classical) Conditioning

Learning an overt motor response to a conditioned stimulus. A classic example is eyeblink conditioning, where a tone (conditioned stimulus) paired with a puff of air to the eye (unconditioned stimulus) eventually triggers a conditioned blink. This form of learning relies heavily on the cerebellum, along with the hippocampus and prefrontal cortex.

Associated with Cerebellum.

Emotional Conditioning

Classical conditioning in which the unconditioned response is an emotion, such as pairing a neutral visual stimulus with a loud noise to produce a conditioned anxiety response. Emotional conditioning is mediated by the amygdala.

Associated with Amygdala.

Explicit Memory Organization: Addressing Systems

Scheme to organize memories in which each memory is given a unique address that can be used it to look it up. System is used in a library and the internet. Simply a long list of addresses that must be searched.

Limitations: Retrieval time slows down as total stored data increases, a single digit error produces unpredictable/random errors, and cannot generate related clues if an exact address entry is missing.

Explicit Memory Organization: Content-Addressable Storage

Scheme by which to organize memories in which the content of the memory itself serves as the storage address.

Advantages: Search time remains fast regardless of total accumulated knowledge, errors yield “near misses” related in meaning or category (e.g., accidentally recalling Chris Pine instead of Chris Evans), and the system can retrieve targets despite flawed cues and can make logical inferences.

Explicit Memory Organization: Hierarchical Theory

Theory of memory organization in which concepts are organized in a taxonomic hierarchy (i.e. animal → birds → canary) and characteristic properties are stored at each level. It contains a network composed of 2 basic elements: nodes and links.

Structural Element of Hierarchical Theory: Nodes

Representation of concepts in hierarchical and spreading activation theories.

Activation

The level of energy or excitement of a node, indicating that the concept the node represents is more accessible for use by the cognitive system.

Structural Element of Hierarchical Theory: Links

Representation of the relationship between concepts. In the hierarchical model, the links are labeled (i.e. “has this property”), whereas in spreading activation models, the links simply pass activation from one node to another.

Key Mechanism of the Hierarchal Model: Property Inheritance

A characteristic of some models of categorizations; concepts inherit properties from the concepts the are higher in the hierarchy. For example, an animal is a living thing and it inherits properties of living things. Chicken inherit the properties “must breathe” and “must eat” from the concept animal. Important for inference based answers.

Key Mechanism of the Hierarchal Model: Cognitive Economy

Properties are stored only once at the highest possible category level. The principle of designing a cognitive system in a way that conserves resources. For example, memory storage space. Found not to be true in the brain, when studied participants wrote information that was one or two levels higher in the hierarchy.

Limitations of the Hierarchical Model

Typicality Effect Violations: Fails to explain why participants verify “A robin is a bird” faster than “An ostrich is a bird,” despite both being one level away.

Hierarchy Violations: Fails to explain why “A gorilla is an animal” is verified father than “A gorilla is a mammal”

Redundant Storage: Participants spontaneously list properties like “flies” directly for specific birds, proving properties are stored redundantly rather than strictly at the superordinate level.

Explicit Memory Organization: Spreading Activation Model

A model in which memory is conceived as a network of nodes connected by links and in which activation spreads from node to node via the links. Addressed shortcomings of the hierarchical models. Links represent associations between semantically related concepts. Instead of hierarchy with groups and categories, it is just concepts associated with each other through meaning.

Structural Element of Spreading Activation Theory: Semantic Network

Name given to all the nodes and links in a spreading activation model. Nodes become active through stimulation from the environment. Activated nodes send a high proportion of their activation to closely related concepts.

Structural Element of Spreading Activation Theory: Weighted Links

Links represent semantic association strength (weighted links) rather than strict rigid hierarchies.

6 properties of a Semantic Network

1. Operates via processing units (each unit represents a concept)

2. Operates via activation states (each unit has its own state of activation. an amount of “energy” at a given moment)

3. Operates via output functions (units pass activation to one another)

4. Operates via connectivity patterns/link weights (units are connected to one another by links of different strengths)

5. Operates via activation rules to combine inputs (a unit follows a rule to integrate the activation sent to it by other units via links)

6. Operates via earning rules to modify link weights over time (the knowledge of the network is in weights, so there must be a mechanism to change the weights if the model is to learn)

Evidence Supporting Spreading Activation Theories

Semantic Priming Experiment: Lexical decision task where participants decide if letter strings are real words. Participants identify the target word nurse significantly faster when preceded by a semantically related prime (doctor) video than an unrelated prime (radio). Concluded that activation spreads from an active node to adjacent semantically connected nodes.

Repetition Priming Bias: Exposure to words on a prior list creates a measurable bias during subsequent word-stem completion, fragment completion, or category exemplar generation tasks up to an hour later. Proves that node activation persists over time, leaving concepts temporarily easier to access.

Semantic Priming

Effect in which performance of a task is biased by the person having earlier viewed semantically related words or pictures.

Bias

In signal detection theory, a measure of the participants bias to either report or not report the presence of a signal. Measured independently. Refers to the increased probability or speed of accessing a previously activated concept during priming tasks.

Overall Structure of Long-Term Memory

A. Long Term Memory

B. Implicit and Explicit Memory

Explicit Memory: Semantic and Episodic

Implicit Memory: Motor Skills, Repetition Priming, Conditioning

Motor Skills: Adaptation and Sequencing

Conditioning: Classical and Emotional