Programmed control of aimed movements revisited: The role of target visibility and symmetry

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Used 12 Ss to study reaction time (RT) prior to starting a 2-mm amplitude aimed movement as a function of target size and experimental procedure. Consistent with a report by S. T. Klapp (see record 1975-30850-001), choice RT increased as target size decreased when the visual signal that initiated the RT interval also indicated which of 2 targets was to be hit. This result implies response programing during the reaction time interval, with more programing time for slower movements to smaller targets. By contrast, in a simple RT procedure, there was no effect of target size on RT, suggesting that the response can be programed in advance when the appropriate target is precued. This provided a control for speed-accuracy trade-off, supporting the programing interpretation of the choice RT result. In another condition with 8 Ss in which both targets could be viewed while waiting for the auditory signal that initiated the RT interval and indicated which target to hit, choice RT was independent of target size provided that both possible targets on each trial were of the same size. The overall results suggest that response programs include both spatial and temporal information, and that parallel programing of different spatial goals is possible provided that the responses are of the same duration. (23 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved)

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