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Christine Gamble, Joo-Hyun Song; Distinct influences of size-contrast illusion on action preparation and execution. Journal of Vision 2015;15(12):595. doi: 10.1167/15.12.595.
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© ARVO (1962-2015); The Authors (2016-present)
Introduction: Many previous studies examining visually-guided actions within size contrast illusions have shown dissociation between vision for perception and vision for action. However, such investigations have focused almost exclusively on movement execution, ignoring other aspects of movement such as preparation. Additionally, the majority of these studies have examined grasping movements, with little research conducted on other types of hand movements like pointing, or other effectors such as the eyes. Methods: To determine the influence of illusion on movement preparation and movement execution in different forms of visually-guided action, we manipulated both physical and perceptual target size using a variation of the Ponzo illusion. Participants performed a two-alternative forced choice task in which they pointed and made saccadic eye movements to targets. We analyzed two aspects of both pointing and saccades: movement preparation, measured by initiation latency and movement execution, measured by movement time. Results: Across both tasks we found that the preparation leading to pointing and saccades was modulated by the perceived as well as the physical sizes of targets, while execution was influenced solely by physical size. Thus movement preparation fails to show the classic perception-action dissociation—measures of action being immune to illusion despite its influence on perception—while movement execution does show this dissociation. Furthermore, we showed that within participants the extent to which illusion influenced the preparation of saccades and reaching was significantly correlated. Conclusion: Thus, we suggest that a shared mechanism modulates the preparation of visually-guided action across the two effectors of pointing and saccades. We propose that this mechanism is responsible for illusion’s influence on movement preparation but not movement execution. Our ongoing studies examining coordinated hand and eye movements further explore the influence of illusion on visually-guided action, and the relationship between the preparation and execution of individual action effectors.
Meeting abstract presented at VSS 2015
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