PS2015

Lecture 2

Cognitive Models of Memory

Cognition Lecture 2 Key issues where cognitive psychology parts from common sense

» 1. Deterministic (by virtue of mechanisms)

» 2. Underlying causation is hidden from us (introspectively)

» 3. Cognitive psychology has no soul (no single controlling centre)

What type of Memory is Episodic Memory?» Phenomena - what does the model have to explain?

» Distinguishing or ‘core’ features

» Consensus ‘Functional architecture’

Chapter 1, 5 and 6 from Reisberg

The Mind Is…

A machine made of ‘stupid’ mechanisms that can interact with one another via connections within neural tissue

Computer analogy is latest in long line of machine comparisons (weaving looms, watermills, aquaducts…)

E.G. the library metaphor for Memory• Organization is the key

• New experiences and knowledge are filed away systematically• Search and retrieval operations can take advantage of the library

organisation to speed things up

It may depend upon your ‘span of attention’

How Many Experiences Have you Had?

1

10

100

1000

10000

100000

1000000

10000000

100000000

1000000000

HOUR DAY WEEK MONTH YEAR DECADE

TIME

Nu

mb

er o

f ep

iso

des

(lo

g)

Memories Accumulate Across the Life Span

100000

1000000

10000000

100000000

10year old 20 year old 30 year old 40 year old 50 year old 60 year old 70 year old 80year old

Age

Num

ber o

f Epi

sode

s in

Mem

ory

(log)

It may depend upon the ‘fidelity’ of episodic encoding

Low fidelity

Hi-fidelity

The Mind Is…

• Both resistant and misleading to introspection• E.g. memory search mechanisms are ‘hidden’

• E.g. retrieval operations can generate realistic false memories (lecture 4)

• Particularly with regard to causal (functional) mechanisms• E.G. the library metaphor for Memory

• How is the library managed? By a librarian?

Cognitive Psychology has no Soul

• Reason 1 concerns the brain:-• a. There may not be a single,

controlling brain ‘centre’

• b. Circuits can work independently of one another

• Reason 2 concerns function:-• No Homunculi allowed!

• they generate an infinite regress which leaves nothing explained

Is anyone behind the wheel?

Some Common Sense about the Self

1. Continuous over time, past, present and in the future

2. Singular

3. Responsible for controlling the mind and the body (‘will power’)

4. Determines your individuality

Key basic assumptions

Our conscious experiences are ‘constructed’

Many different mechanisms may exist to produce the varieties of conscious experience

Some experiences, associated with higher cognition, may arise from simpler mechanisms working together in concert

Experimental work may allow us to isolate and study each simple mechanism, and how they interact with one another

Cognitive Models

Cognitive models are appropriate because they ‘fractionate’ the mind

Cognitive models imply that ‘Reality’ is a construct

Initial questions for any cognitive model» How many mechanisms?» What does each mechanism do?» How do the mechanisms work together within a ‘functional

architecture’?

Episodic Memory

• Phenomena• What is an episode? A memento?

• Core features

• ‘Functional architecture’

Episodic Memory has core features

Memory for specific events from your past

Involves retrieval of content and context (what happened, when it happened and where did it happen)

Associated with a particular kind of conscious experience ‘mental time travel’ re-experiencing past sights, sounds, etc

Episodic Memory is remarkable

But also fallible, in many different ways

E.g. encoding is (normally) imperfect and/or incomplete

We fail to retain (consolidate) information, and possibly alter the nature of what is retained anyway (leaving the ‘gist’)

Retrieval errors: PTSD, intrusive recollections

‘False’ memories

Processing Stages in Episodic Memory

ENCODING: capture an experience in a trace Form multiple individual records of attended information Associate (bind each co-active individual record )

CONSOLIDATION: make the trace information ‘permanent’ Abstraction of semantic gist? Formation of multiple retrieval pathways ‘offline’ playback mechanisms during sleep and quiet states

RETRIEVAL: access the (correct) trace Access to the records of attended information via a retrieval cue Re-activation of attended information and its context

Episodic Memory ‘Architecture’

ConsolidationMechanisms

AttentionalControl

Encoding Storage Retrieval

AttentionalControl

SemanticRecords

PerceptualRecords

Binding

ContextSemanticRecords

PerceptualRecords

Binding

Context

This diagram reflects a widely accepted general consensus

A Specific Example The constructive memory framework (CMF)

• Schacter, DL, Norman, KA, and Koutstaal, W. (1998). The cognitive neuroscience of constructive memory. Annual Review of Psychology, 49, 289-318.

• Invokes multiple brain regions• Some involved in encoding and retrieval• Some involved in either encoding or retrieval

• Comprising multiple functions that must interact dynamically with one another

CMF Neuroanatomy The hippocampal formation

‘Indexing’ of episodes: exactly how is unknown Necessary both for encoding and retrieval Damage leads to dense retrograde and anterograde amnesia

The frontal lobes Strategic control over memory: exactly how is again unknown! Damage leads to confabulations, delusions, heightened false memory,

source amnesia

The entire ‘association’ neocortex Representation of experienced content Damage should lead to loss of specific content of prior episodes

CMF Retrieval Functions

Retrieval ‘focus’

Access to the records of attended information via a retrieval cue (by hippocampal pattern completion)

Inhibition of irrelevant information

Re-activation of episodic content (held in the neocortex)

Monitoring/evaluating retrieval products (prefrontally mediated)