Evidence limiting the subtended-angle hypothesis of response-programming delays.

In 1991 Sidaway proposed an alternative explanation to account for the traditional effect of response complexity on programming time. He suggested that rather than number of movement parts per se, it is the directional accuracy demand of a response, as quantified by the "subtended angle," that constrains the movement initiation and produces programming delays. In Sidaway's experiments targets were positioned so that the first target was always closest to the starting position, with subsequent targets positioned further away from the start. This study tested the subtended-angle hypothesis by placing the first target furthest from the starting position, with subsequent targets struck by reversing direction and coming back toward the start. 30 subjects performed two aiming responses, a discrete 1-TAP condition and a serial 3-REVERSE condition. Because the subtended angle was identical in both conditions, there should be no difference in programming time. Our analyses, however, showed a significant effect for number of targets. Mean reaction time was longer for 3-REVERSE than for 1-TAP. These results argue against a strict constraint interpretation based on subtended angle and suggest that, under certain conditions, number of movement parts can still affect delays in response programming.