ERP correlates of retrieval orientation: cue-related and item-related measures

Jane E. Herron and Edward L. Wilding,

School of Psychology, Cardiff University

Introduction

• Episodic retrieval can be fractionated into pre-retrieval processes, retrieval

itself, and post-retrieval monitoring and evaluation processes.

• Tulving (1983) introduced the notion of ‘retrieval mode’, a generic mnemonic

set that allows stimuli to be processed primarily as cues for episodic retrieval.

Mode was thought to remain invariant across different episodic tasks.

• Different episodic memory tasks have been hypothesised to additionally invoke

task-specific pre-retrieval processes - retrieval ‘orientations’ – that vary

according to the type of episodic information that is to be retrieved (Rugg &

Wilding, 2000).

• Retrieval orientations are thought to operate as tonically maintained ‘sets’ that

influence the way in which stimuli are processed, in order to facilitate retrieval

of the required episodic information.

• Recent studies have provided neural evidence for the existence of retrieval

orientations (e.g. Dobbins et al., 2003; Werkle-Bergner et al., in press; Simons

et al. 2005; Robb & Rugg, 2002; Herron & Wilding, 2004), some using cue-

related designs and others item-related designs;

1. Cue-related: Cue subjects item-by-item as to what type of episodic

information they should retrieve and examine correlates of the cue.

2. Item-related: Examine item-related activity for differences due to

the type of retrieval task, either by examining correlates of correct rejections or

by looking for main effects of retrieval task that do not interact with old/new

item type.

• Despite the variation in experimental design, a common finding is that

correlates of orientation appear at left fronto-temporal scalp and brain regions.

• The following four experiments from our lab employ a combination of cue-

related and item-related analyses to examine retrieval orientation.

• Designed to dissociate correlates of retrieval mode from correlates of retrieval

orientation using a cue-related method (10 study-test blocks):

Experiment 1

• Correlates of retrieval mode and retrieval orientation should be evident as

commonalities (mode) and differences (orientation) between ERPs elicited by

the episodic cues relative to the semantic cue.

• ‘Task?’ = Operations; ‘Location?’ = Location; ‘Movement?’ = Semantic

STUDY

• 12 items per block.

• 6 items rated for animacy (3 shown on the left of the screen, 3 on the right).

• 6 items rated for pleasantness (3 on the left, 3 on the right).

• Binary response (i.e. X = animate, Z = inanimate).

TEST

• 24 items (12 old, 12 new).

• Episodic (‘Task?’ or ‘Location?’) and semantic (‘Movement?’) cues each appear before 8 items.

• Cue-types presented in pairs

• Self-paced, 3-way response for each cue-type (e.g. old left, old right, new)

Cue Test item2 second interval

Recording Parameters

• Sampling rate = 8 ms (epoch length = 2048 ms, pre-stimulus baseline = 104

ms, cue-target interval = 2 seconds).

• EOG correction employed for all participants. Linked-mastoid reference.

• 25 channel recordings (based on 10/20 system):

Results: Behaviour

• Accuracy was not affected

by task or switch/stay status

(although greater for new

than for old items).

Accuracy

RT Hits

CRs

Ops (switch)

Ops (stay)

Location (switch)

Location (stay)

Semantic (switch)

Semantic (stay)

Ops (switch)

Ops (stay)

Location (switch)

Location (stay)

Semantic (switch)

Semantic (stay)

• RTs were faster for ‘stay’

than for ‘switch’ trials, and

slower for the Operations

task than for the other two

tasks.

• Correlates of mode and orientation were evident on stay trials only:

Results: ERPs

F5 F6

0 800ms 0 800ms

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10µV

Operations Location Semantic

C5 C6

Operations - Semantic

1.4

0.8

-0.2

0.4

-0.6

Location - Semantic

0.0

-1.0

-0.5

1.5

1.0

Operations - Location

1.6

1.2

0.2

-0.2

0.8

• As in previous studies, correlates of retrieval mode were observed over right

frontal scalp regions and had a delayed onset. The data also provided neural

evidence to support the concept of retrieval orientation, indicating that orientation

also had a delayed onset.

• However, switch trials had a mixed cue history (i.e. which task participants were

switching from) and correlates of retrieval orientation may have been influenced by

the task that participants were switching from, as well as the task into which they

were switching.

• Experiment 2 replicated Experiment 1, but only employed the two episodic cues in

alternating pairs so that all switch trial ERPs had identical trial histories within each

retrieval task, and subjects were no longer switching in and out of retrieval mode.

There were also now sufficient trials to examine item-related ERPs for orientation

effects.

Experiment 1: Summary

Experiment 2: Behaviour

• Accuracy did not differ either by cue-type or by switch/stay status.

• Hit RTs were significantly slower for the Operations than for the Location

task, and for switch than for stay trials.

• CR RTs were significantly faster than Hit RTs, but were not affected either

by cue-type or by switch/stay status.

ACCURACY (%) RT (ms)

0102030405060708090

100

Ops(switch)

Location(switch)

Ops(stay)

Location(stay)

Hits

CRs

0

500

1000

1500

2000

2500

Ops(switch)

Location(switch)

Ops (stay)

Location(stay)

Switch Cues:

Cz

Pz

F5 F6

C5 C6

P5 P6

Fz

0 800ms 0 800ms 0 800ms

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10µV

OPERATIONS CUE (SWITCH)

LOCATION CUE (SWITCH)

Experiment 2: ERPs

Stay Cues:

Cz

Pz

F5 F6

C5 C6

P5 P6

Fz

0 800ms 0 800ms 0 800ms

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OPERATIONS CUE (STAY)

LOCATION CUE (STAY)

• No independent retrieval task effects were detected for item-related ERPs.

• A significant effect of cue type was found for switch trials but not for stay trials.

Although this effect had similar spatio-temporal characteristics as that seen in

Experiment 1, the polarity of the effect was reversed. It is possible that this

polarity reversal was due to differences in cue history.

• The finding that this effect was significant on switch trials suggests two

possibilities:

1. A retrieval orientation is not adopted until retrieval mode is engaged.

2. As switch trials were predictable in this experiment (due to alternating

pairs), subjects had sufficient time to adopt a retrieval orientation by

predicting the switch cues.

Experiment 2: Summary

• Experiment 3 tested the second hypothesis by replicating experiment 2, but

inserting randomised ‘catch’ trials into the memory test sequence:

• Accuracy did not differ either by cue-type or by switch/stay status.

• Hit RTs slower for the Operations than the Location task, and for switch than for

stay trials.

Experiment 3: Rationale and Behaviour

ACCURACY (%)

0102030405060708090

100

Ops(switch)

Location(switch)

Ops(stay)

Location(stay)

Hits

CRs

RT (ms)

0

500

1000

1500

2000

2500

Ops(switch)

Location(switch)

Ops (stay)

Location(stay)

Switch trials:

Cz

Pz

F5 F6

C5 C6

P5 P6

Fz

0 800ms 0 800ms 0 800ms

+

10µV

OPERATIONS CUE (SWITCH)

LOCATION CUE (SWITCH)

Experiment 3: ERPs

Stay trials:

Cz

Pz

F5 F6

C5 C6

P5 P6

Fz

0 800ms 0 800ms 0 800ms

+

10µV

OPERATIONS CUE (STAY)

LOCATION CUE (STAY)

• No independent retrieval task effects were detected for item-related ERPs.

• As in Experiment 2, a significant effect of cue type was found for switch trials but

not for stay trials. This effect was again maximal over left fronto-temporal sites

between 700-1900 ms, and was of the same polarity as that observed in

Experiment 2.

• The finding that correlates of retrieval orientation were significant on switch trials

in Experiments 2 & 3 suggests that one is able to switch retrieval orientation

immediately, as long as one is already in retrieval mode (and that engagement

in retrieval mode must be achieved before orientation can be adopted).

• The findings of Experiments 2 & 3 indicate that this correlate of retrieval

orientation reflects the initial adoption of an orientation.

Experiment 3: Summary

• Other studies employing blocked designs have reported item-related correlates

of retrieval orientation, arguably reflecting processes related to orientation

maintenance. These effects were not evident in our experiments, probably

because they required rapid switching between different orientations (Wilding &

Nobre, 2001).

• We attempted to induce significant item-related orientation effects in Experiment

4 by blocking the two retrieval tasks used in the previous experiments (all other

aspects of the design remained identical). Occasional ‘catch’ trials ensured that

subjects still attended to the cues.

• Item-related orientation effects should be evident in a blocked design if these

are related to the maintenance of an orientation. Conversely, if our cue-related

orientation effects reflect the initial adoption of a retrieval orientation, then these

effects should not be observed in a blocked design.

Experiment 4

Results: Behaviour

ACCURACY (%) RT (ms)

• Accuracy did not differ by cue-type.

• Hit RTs slower for the Operations than for the Location task.

0

500

1000

1500

2000

Operations Location

0

20

40

60

80

100

Operations Location

Hits

CRs

Cues:

Fz

Cz

Pz

F5 F6

C5 C6

P5 P6

0 800ms 0 800ms 0 800ms

+

10µV

OPERATIONS CUE

LOCATION CUE

Results: ERPs

Items:

Fz

Cz

Pz

F5 F6

C5 C6

P5 P6

0 800ms 0 800ms 0 800ms

+

10µV

OPERATIONS ITEMS

LOCATION ITEMS

• Unlike Experiments 1-3, no cue-related retrieval task effects were detected in

Experiment 4.

• A significant main effect of retrieval task was observed for item-related ERPs in

Experiment 4, maximal over left- and mid-temporal sites. As this effect did not

interact with item type, it fulfils the criteria for a correlate of retrieval orientation.

The distribution of this effect is similar to item-related orientation effects reported

in other studies, and arguably reflects processes contingent upon the

maintenance of orientation across items.

• The findings from Experiments 1-4 provide evidence for two dissociable

correlates of retrieval orientation. The cue-related orientation effects reported in

Experiments 1-3 appear to reflect the initial adoption of a retrieval orientation,

whereas the item-related effect reported in Experiment 4 appears to reflect

processes contingent upon the maintenance of an orientation across items.

General Summary

Cz

F5

C5

Fz

+

10µV OPERATIONS (SWITCH) LOCATION (SWITCH)

OPERATIONS (SWITCH) LOCATION (SWITCH)

+

10µV

Cz

F5

C5

Fz

CzC5

+

10µV OPERATIONS LOCATION

2.0

1.0

0.5

0.0

1.2

0.4

0.0

-0.2

2.0

.0

0.5

-1

800ms 800ms

800ms 800ms

800ms 800ms

EXPERIMENT 2: CUES

EXPERIMENT 3: CUES

EXPERIMENT 4: ITEMS

800 – 1900 ms

800 – 1900 ms

800 – 1900 ms

References

• Dobbins I.G., Rice H.J., Wagner A.D., Schacter D.L. (2003) ‘Memory orientation and success:

separable neurocognitive components underlying episodic recognition.’ Neuropsychologia, 41(3),

318-33.

• Herron J.E. & Wilding E.L. (2004) ‘An electrophysiological dissociation of retrieval mode and retrieval

orientation.’ Neuroimage, 22(4), 1554-62.

• Simons J.S., Gilbert S.J., Owen A.M., Fletcher P.C., Burgess P.W. (in press) ‘Distinct Roles for Lateral

and Medial Anterior Prefrontal Cortex in Contextual Recollection.’ Journal of Neurophysiology.

• Tulving, E., (1983) ‘Elements of Episodic Memory’. Oxford: Oxford University Press.

• Robb W.G. & Rugg, M.D. (2002) ‘Electrophysiological dissociation of retrieval orientation and retrieval

effort.’ Psychonomic Bulletin and Review, 9(3), 583-9.

• Rugg, M. D., Wilding, E. L., (2000) ‘Retrieval processing and episodic memory.’ Trends in Cognitive

Sciences, 4, 108-115.

• Werkle-Bergner, M., Mecklinger, A., Kray, J., Meyer, P. & Duzel, E. (in press) ‘The control of memory

retrieval: Insights from event-related potentials.’ Cognitive Brain Research.

• Wilding E.L. & Nobre A.C. (2001) ‘Task-switching and memory retrieval processing:

electrophysiological evidence.’ Neuroreport, 16;12(16), 3613-7.

Experiment 2 – ‘Operations’ Old/New: Switch Trials

Cz

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F5 F6

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Fz

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HITS

CRS

Experiment 2 – ‘Operations’ Old/New: Stay Trials

Cz

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F5 F6

C5 C6

P5 P6

Fz

0 800ms 0 800ms 0 800ms

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HITS

CRS

Experiment 2 – ‘Location’ Old/New: Switch Trials

Cz

Pz

F5 F6

C5 C6

P5 P6

Fz

0 800ms 0 800ms 0 800ms

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HITS

CRS

Experiment 2 – ‘Location’ Old/New: Stay Trials

Cz

Pz

F5 F6

C5 C6

P5 P6

Fz

0 800ms 0 800ms 0 800ms

+

10µV

HITS

CRS

Experiment 3 – ‘Operations’ Old/New: Switch Trials

Cz

Pz

F5 F6

C5 C6

P5 P6

Fz

0 800ms 0 800ms 0 800ms

+

10µV

HITS

CRS

Experiment 3 – ‘Operations’ Old/New: Stay Trials

Cz

Pz

F5 F6

C5 C6

P5 P6

Fz

0 800ms 0 800ms 0 800ms

+

10µV

HITS

CRS

Experiment 3 – ‘Location’ Old/New: Switch Trials

Cz

Pz

F5 F6

C5 C6

P5 P6

Fz

0 800ms 0 800ms 0 800ms

+

10µV

HITS

CRS

Experiment 3 – ‘Location’ Old/New: Stay Trials

Cz

Pz

F5 F6

C5 C6

P5 P6

Fz

0 800ms 0 800ms 0 800ms

+

10µV

HITS

CRS

Experiment 4 – ‘Operations’ Old/New

Fz

Cz

Pz

F5 F6

C5 C6

P5 P6

0 800ms 0 800ms 0 800ms

+

10µV

HITS

CRS

Experiment 4 – ‘Location’ Old/New

Fz

Cz

Pz

F5 F6

C5 C6

P5 P6

0 800ms 0 800ms 0 800ms

+

10µV

HITS

CRS