Memory and Cognition Lecture 10: Filling in the gaps… ENCODING RETRIEVAL Seeing Word Hearing Word MTL

The story so far… We want to read a persons 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 Event-Related Potentials (ERPs) STiming SUpper limit on time it takes for neural processing to differ STime course of a process (onset, duration, offset) SLevel at which a process is engaged SEngagement 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 Brains 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 activity ¤Due to radiation dose, only a limited number of scans can be taken from each subject

Magnetic Resonance Imaging (MRI) l Put head into a strong magnetic field l Water protons align themselves with respect to the field l alignment is then perturbed by radio- frequency pulses l non-invasive and fast (few seconds) l protons relax back into alignment, giving off a signal l relaxation signals can reveal l tissue type l physiological state (e.g. blood oxygenation) l 3D position in the magnetic field

Stimuli 0 Time Retrieval success!!Retrieval failure Consolidation Mechanisms Attentional Control EncodingStorage Retrieval Attentional Control Semantic Records Perceptual Records Binding Context Semantic Records Perceptual Records Binding Context

Focussed Search Retrieve / InhibitMonitor Stimuli 0 Time Retrieval success!!Retrieval failure

cue onset Ecphory/ inhibition Monitoring Retrieval Perception/ attention Pattern completion/ Binding selective attention Stimuli Time CMF{retrieval}

Stimuli Time 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 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) MTL Encoding MTL Retrieval TIME Visual Auditory MTL Encoding MTL Retrieval

Do ERPs reveal 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 l Studied SEEN items l Studied HEARD items l Unstudied NEW items ERP retrieval effects for each sensory modality:- l SEEN – NEW difference l HEARD – NEW difference

No! ERPs are insensitive to differences in modality at retrieval Recall auditory episodeRecall visual episode As retrieval ends… As retrieval begins…

ERP 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 Consolidation Mechanisms Attentional Control EncodingStorageRetrieval Attentional Control Semantic Records Perceptual Records Binding Context Semantic Records Perceptual Records Binding Context

Does encoding temporarily stop when retrieval occurs?