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Joo-Hyun Song, Ken Nakayama; Selecting and pointing: Consecutive serial processing?. Journal of Vision 2005;5(8):384. doi: 10.1167/5.8.384.
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© ARVO (1962-2015); The Authors (2016-present)
Visually guided motor behavior has been generally assumed to comprise two serial stages: response selection followed by motor execution. However, McPeek, Skavenski & Nakayama (2000) showed that multiple saccades could be programmed concurrently with a very short inter-saccadic interval (0–100 msec). Thus the cost of incorrect initial saccades was reduced by short latencies between movements. Does the same pattern occur for manual pointing where the massive arm would cost substantially more in incorrect movements?
Subjects were required to point to a single target or an odd colored target in a search array. Finger trajectories were sampled at 120Hz using a Polhemus device. In the search condition, highly curved trajectories were observed, showing that similar to eye movements, initial pointing was to a distractor and that quick, successively planned arm motion ensured the correct pointing response. In contrast, if the subject waited longer before movement execution, fewer curved trajectories were observed. However, because the latency of such a correct movement was relatively long, the quick strategy, requiring online, possibly concurrent processing was no more costly in overall time. This suggests that in the motor planning of the arm, simple selection followed by execution is not necessarily the optimal strategy. We should thus conceive of visuo motor behavior as an online process, with different multiple goals and plans being implemented concurrently as visual information is processed.
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