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Shane Kelly, Matthew Peterson, Wilsaan Joiner; The Spatial Separation of Movement Goals and Preparation Time Determines Single vs. Averaged Saccade Motor Plans. Journal of Vision 2017;17(10):905. doi: https://doi.org/10.1167/17.10.905.
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Motor program theory assumes that control resides over abstract representations of actions (programs or plans), and that a plan is selected and executed during voluntary movement (Adams, 1971). However, when the goal between two potential targets is ambiguous, the motor output is distinct from movements made to a single goal. These movements are often called averaged or intermediate movements because the output resembles a combination of the two possible plans. This pattern of behavior is observed for quick eye movements (saccades). When two visual targets are presented in close proximity the eyes tend to land in between the two (saccade averaging, the global effect; Coren & Hoenig, 1972). Although saccade averaging is typically observed when the stimuli are close and the eye movements are made with little preparation time, the exact spatial and temporal conditions in which two saccade motor plans are averaged is undefined. Recently, Haith and colleagues (2015) examined averaged movements during a time restricted visually guided reaching task. The target shifted a variable distance and at different times before reach onset, providing limited time to re-prepare the movement plan. Here, we applied the same paradigm and framework to saccadic eye movements. In addition, to confirm when more than one motor plan is output, we created two models to compare to our observed data. One model assumed averaging and the other assumed only one motor plan could be executed at a given time. We tested subjects with target displacements of 20, 30, 40, 60, and 90 degrees of separation. Using Bayesian model comparisons, our results demonstrate that averaging of two saccade plans occurs during a specific temporal range when the displacement between potential targets is small (20, 30, 40), but across the entire temporal range, only one motor plan is output at the larger displacements (60 and 90).
Meeting abstract presented at VSS 2017
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