Memory systems

Off-line processing, consolidation, and interference

Instructions and motor learning

• Green and Flowers (1991)• Wulf (1997)• Verdolini-Marston & Belota (2003)• Boyd & Winstein (2004)

Purpose

• “Complex” skill learning (i.e. real learning)– Occurs in context of both explicit and implicit

processes– Trying to understand the interactivity of the two

systems in learning

Two views of interaction

• Independent– Explicit memory arises from “witnessing” implicit

learning and does not assist it– The different systems emerged from different

origins• Integrated– Explicit memory is a necessary part of acquiring

implicit memory– Explicit memories are transformed into implicit

Method

• Provide explicit instruction, learn implicit task– Integrated – explicit should help– Independent – should have either no effect or hinder

learning• Serial interception sequence learning

– http://reberlab.psych.northwestern.edu/SISL/v0.2.0/SISL.html

• Like a continuous version of the classic sequence learning task– Guitar hero!

• 12 item repeating sequence

Task

• “catch” the balls using the appropriate keys

Method

• 2 groups – – Explicit:

• memorize the sequence• Watch the balls drop without hitting keys• Print out of sequence visible as they watch• Self-paced

– Implicit – none of the above– All:

• 24 random cues for familiarization• 6 X 480 learning trial blocks (384 sequenced, 96 novel)• 540 trial test block

– 3 different sequences – I from practice– 5 reps per sequence (60 trials)– Used to show performance diffs due to learning

Method

• Following practice:– Explicit recognition test• 5 different sequences have two reps each• Rated confidence that sequence was the one practiced

– Explicit recall task• Try to produce sequence using keys without balls being

seen

Results

• No group differences in performance or learning

Results

• Differences in explicit recall…

Only statistical difference – explicit group could produce the sequence

better than the implicit group

Conclusions

• Independent, multiple memory systems ideas are better supported– This provides direct evidence against the

integrated, single system argument– Implicit learning here is not aided by explicit

knowledge– …but it’s not hurt either (unlike earlier studies)– Task specific issues?• Is this learning coordination?

Historically…

• H.M.• Squire & others (e.g. Cohen and Squire 1980)– Declarative and procedural memory systems are

independent• Alzheimer’s: declarative impaired, procedural not• Huntington’s: procedural impaired, declarative not• fMRI scanning: procedural & declarative “work” lights

up different neural circuitry

New evidence…

• Willingham (1997)– Activity within medial temporal lobe and striatum

associated• Brown and Robertson (2007a and b)– Learning word list after motor skill impairs motor

skill– Learning motor skill after word list impairs word

learning

Interference paradigm

• Consolidation and reconsolidation…– Susceptibility to interference, and time:

Lines of evidence…

• A shared resource?– Medial temporal lobes active during both

declarative and procedural processing.• Coupling causing shift from independence?– Damage to frontal lobe prevents interference– Wakefulness vs. sleep – dorsolateral prefrontal

cortex invoked when awake but not when asleep• Seems to be that frontal lobe makes MTL and Striatum

interfere

Interference possibilities & findings

Role of dorsolateral prefrontal cortex…

Function of interference…

• When learning motor skill first…– Interference prevented by stimulating motor

cortex• Neither memory impaired or enhanced when

interference prevented– Interference independent of memory processing– Stimulated areas (DLPFC, M1) seem to be

producing the interference…why?

Function of interference…

• Why?– New memories are unstable at time of learning– Retrieved memories are unstable when recalled• Maybe instability of both makes for better

reorganization of the paired memories?

– DLPFC or M1 may• Exert executive control over memory• Select memories susceptible to interference

Brain state & processes

• Areas of brain interfere when awake, but not when asleep– When awake, memories are organized interactively– When asleep they are organized independently

• Learning…– Independent acquisition but interactive after learning?

• Aging– DLPFC function alters with age. Youth – mature – old.

Manipulating interference

• Altered sequence of learning to avoid interference?– Maybe, but what’s the function of the

interference?– Maybe it leads to greater memory integration?

Memory stability

• New memories become resistant to interference over a few hours. – Circuits effecting this change depend on type of

practice…• Single block – M1• Multiple blocks – DLPFC

– “Offline” processes stabilize learning.

Offline learning

• Can be enhanced by– Sleep (motor learning 20-30%)– Praise– Cues at encoding

• Learning & consolidation (offline learning) rely on similar brain areas and chemical processes– Circuitry in bird song similar when actually singing

and when dreaming.

Retrieval and stability

• Retrieved memories can be interfered with– But only when new information is to be paired

with retrieved information– Possible link with need to integrate new with old

memory