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Darian Cheng, John DeGrosbois, Jonathan Smirl, Gordon Binsted; Sequence effects during manual aiming: A departure from Fitts's Law?. Journal of Vision 2010;10(7):1064. doi: 10.1167/10.7.1064.
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© ARVO (1962-2015); The Authors (2016-present)
In 1954, Paul Fitts forwarded a formal account of the relationship between the difficulty of an aiming task and movement time associated with its completion. While most models used to explain this speed-accuracy tradeoff have been based upon visual feedback utilization and target-derived uncertainty, the idea that speed-accuracy constraints can also be dictated by previous aiming history has been largely ignored. In order to examine whether sequential movements are interdependent, we utilized a sequential-discrete aiming paradigm where the target changed difficulty mid-sequence, but between reaches. Individuals performed an adapted Fitts's task by performing discrete manual aiming movements between two equidistant targets from the midline. Responses were produced in sequences of 20 manual aiming movements separated by a fixed inter-trial-interval of 1 s. Four trial sequences were used in the experiment: in two of the sequences the target widths remained constant throughout trial (wide or narrow), in two sequences the target width changed (wide to narrow, narrow to wide) between the 7th to 12th movements of the sequence. Our main area of interest was in the trials immediately following the change in target width. Namely, we wanted to see if there were any carry-over effects from the preceding target width on the subsequent movements to a different target width. The extant sequential aiming literature suggests individuals plan several movements in advance during sequential movements, as compared to a single movement in isolation. In accord with this view, we demonstrated a gradual change in movement times and movement endpoint distributions following a switch in target width during a reciprocal aiming task. Importantly, this necessitates a transient departure from Fitts's law and highlights the role of visuomotor memory for the planning and execution of movements even in the presence of vision.
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