Presentation on theme: "ERP correlates of retrieval orientation: cue- related and item-related measures Jane E. Herron and Edward L. Wilding, School of Psychology, Cardiff University."— Presentation transcript:
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) CueTest item 2 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.
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) 0 10 20 30 40 50 60 70 80 90 100 Ops (switch) Location (switch) Ops (stay) Location (stay) Hits CRs 0 500 1000 1500 2000 2500 Ops (switch) Location (switch) Ops (stay) Location (stay)
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 (%) 0 10 20 30 40 50 60 70 80 90 100 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)
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 OperationsLocation 0 20 40 60 80 100 OperationsLocation Hits CRs
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
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