Visual Perspective Effects on Action Memory

Abstract

This thesis explores neural activity underlying visual perspective taking during action memory encoding and retrieval. The main hypothesis was that frontal regions, particularly those associated with mirror neurons (inferior frontal gyrus: IFG) would be involved during encoding of actions which occurs when participants merely observe videos of the action. A series of experiments were conducted with action observation tasks using video clips of dynamic actions presented from two visual perspectives (direct perspective vs. translated perspective) involving both action memory encoding and retrieval. In each experiment, participants merely observed the action videos (either a hand reaching action or a disembodied object action) and pressed one of two response keys following a cue according to the task requirements. Neural processing was assessed by electroencephalography (EEG) and behaviour was assessed using reaction time of key press responses to stimuli. The results of Experiment 1 supported the hypothesis by showing that highly significant frontal cortex activity was differentially influenced by visual perspectives during early encoding stages of action observation. This contrasts with the highly significant parietal activity which occurs during retrieval stages. In Experiment 2 we manipulated the task requirements in the retrieval stage, results nearly replicated those of Experiment 1 in terms of early frontal activity, again supporting the role of the mirror neuron system in perspective taking during action encoding. Experiment 3 we replaced the embodied actions with disembodied movements of an object that involved no visual perspective. The results showed a completely different brain activation pattern compared with the earlier perspective- related frontal activity pattern, with early activity in right parietal areas and late activity in left frontal areas for different action direction conditions. These findings confirm that previously-reported frontal activation is not due to factors associated with direction of the movement in space but due to visual perspective taking during encoding of an embodied action. Further analysis ruled out a possible confound of cognitive load, thereby bolstering our conclusions about frontal involvement in visual perspective processing. Taken together, the present thesis suggests that the frontal area, especially the mirror neuron system, plays an important role in visual perspective taking during action encoding, and we suggest that observation of embodied actions might actually be involved in forming motor representations in different perspectives, supporting a key factor in social cognition.