Memory and CognitionMemory and CognitionLecture 10: ‘Filling in the gaps…’Lecture 10: ‘Filling in the gaps…’

ENCODING RETRIEVAL

Seeing Word

Hearing Word

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The story so far…The story so far…

• We want to read a person’s mind from the activity of their brain

• Their mind is composed of lots of interacting cognitive processes

• Each distinct process is carried out by networks of brain regions, each region is probably performing specific functions, but they all work together

• So we need an accurate (or semi-accurate) cognitive model and experimental techniques that can detect changes in brain activity specific to any cognitive process

Functional Inferences Based Upon Functional Inferences Based Upon Event-Related Potentials (ERPs)Event-Related Potentials (ERPs)

Timing Upper limit on time it takes for neural

processing to differ Time course of a process (onset,

duration, offset)

Level at which a process is engaged

Engagement of multiple processes at different times or in different conditions

Early Topography

Late Topography

Electrophysiological Techniques

• Principle advantages• non-invasive

• high temporal resolution

• direct reflection of neuronal activity

• easy to produce event-related potentials by selective averaging of EEG epochs.

• topographic mapping

• Cheap (for EEG but not MEG)

The Brain’s Plumbing

Haemodynamic Techniques

Oxygen and glucose are supplied by the blood as ‘fuel’ (energy) for the brain The brain does not store fuel, so Blood supply changes as needs arise Changes are regionally specific - following the local dynamics of neuronal activity

within a region

Haemodynamic techniques localise brain activity by detecting these regional changes in cerebral blood supply

Positron Emission Tomography (PET)

Samples the entire brain volume homogeneously

Has an effective anatomical resolution of about 10mm or so in group studies

An ‘indirect’ measure of neuronal activityDue to radiation dose, only a limited number of

scans can be taken from each subject

Magnetic Resonance Imaging (MRI)

Put head into a strong magnetic field Water protons align themselves with respect to the field alignment is then perturbed by radio-frequency pulses non-invasive and fast (few seconds) protons ‘relax’ back into alignment, giving off a signal relaxation signals can reveal

tissue type physiological state (e.g. blood oxygenation) 3D position in the magnetic field

Stimuli

0Time - 1 3 4 65 7 92 8

Retrieval success!!Retrieval failure

ConsolidationMechanisms

AttentionalControl

Encoding Storage Retrieval

AttentionalControl

SemanticRecords

PerceptualRecords

Binding

ContextSemanticRecords

PerceptualRecords

Binding

Context

Focussed Search

Retrieve / Inhibit Monitor

Stimuli

0Time - 1 3 4 65 7 92 8

Retrieval success!!Retrieval failure

cueonset

Ecphory/inhibition

MonitoringRetrieval Perception/attention

Patterncompletion/

Binding

‘selective attention’

Stimuli

Time 0.1 0.2 0.40.3 0.5 0.70 0.6

CMF{retrieval}

Stimuli

Time 0.1 0.2 0.40.3 0.5 0.70 0.6

Ecphory?

Monitoring?

Implicit Memory?

Familiarity?

For review see Donaldson, Allan and Wilding (2003) (download from my school of Psych homepage)

Using ERPs to Investigate the Consensus idea Using ERPs to Investigate the Consensus idea of Encoding / Retrieval Overlap…of Encoding / Retrieval Overlap…

• Operationally define different classes of study episode

• Record EEG when instances of each class of episode are recollected

• Form ERPs to each class of recollected episode

• Contrast the magnitude and topography of ERPs for each class of recollected episode

Encoding and Retrieval in vivo…

Olfactory (Gottfried et al, 2004)

and within ‘sensory domain’ too (Woodruff et al., 2005)

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Encoding

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Retrieval

TIMEVisual

Auditory

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Encoding

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Retrieval

Do ERPs revealDo ERPs revealmodality specific retrieval processes?modality specific retrieval processes?

• Subjects SAW and HEARD words at study

• Performed a word-stem (e.g. MOT__) cued recall task

• ERPs were formed to stems completed with Studied SEEN items Studied HEARD items Unstudied NEW items

• ERP retrieval effects for each sensory modality:- SEEN – NEW difference HEARD – NEW difference

No!No!ERPs are ERPs are insensitiveinsensitive to to

differences in differences in modality at retrievalmodality at retrieval

Recall auditory episodeRecall visual episode

As retrieval ends…

As retrievalbegins…

ERP Modality Experiment: ConclusionsERP Modality Experiment: Conclusions

• Multiple retrieval processes, active at different times– Onset ~ 0.5s after retrieval cue!

• Retrieval of ‘visual’ and ‘auditory’ episodes involves common processes. No evidence for modality specific retrieval processes

• ERPs reflect a ‘core component’ of retrieval? – Changes in neocortical activity driven by the Hippocampus

during early stages of retrieval (prior to modality specific activations)?

– Or: attention to retrieval products?

Episodic Memory Mechanisms

ConsolidationMechanisms

AttentionalControl

Encoding Storage Retrieval

AttentionalControl

SemanticRecords

PerceptualRecords

Binding

ContextSemanticRecords

PerceptualRecords

Binding

Context

Does encoding temporarily stop when retrieval occurs?

How Many Experiences Have you Had?

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