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

Distributed Control in Rapid Sequential Aiming Responses

The preparation and on-line control of short, rapid sequential aiming responses were studied in 3 experiments. Participants (N = 12 in Experiments 1 and 2, and 20 in Experiment 3) produced 3-segment responses (a) within self-initiation, simple reaction time (RT), and choice RT paradigms (Experiment 1); (b) without visual feedback under self-initiation conditions (Experiment 2); and (c) with and without visual feedback under simple RT conditions (Experiment 3). In all conditions in which participants initiated movement in response to an external imperative signal, the 2nd response segment was performed consistently slower than preceding and succeeding response segments. That pattern of segmental movement times was found whether or not visual feedback was available but was not evident when participants self-initiated their responses with or without visual feedback. The findings rule out the possibility that subjects' use of visual feedback is responsible for the slowing of the 2nd response segment under RT conditions and suggest that the programming of rapid sequential aiming responses can be distributed in pre- and postinitiation intervals.

Cinematographical Analysis of Movement Pathway Constraints in Rapid Target-Striking Tasks

Several features of the actual movement pathway in two rapid target-striking tasks were quantified by using high-speed cinematography, and whether the movement pathway is constrained as a function of the accuracy demands imposed by the size of the subtended angle was determined. Subjects (N = 16) first hit an 8-cm-diameter target located 10 cm to the left of a start position and then, depending on the condition, moved another 10 cm to hit either a 6-cm- or 1.5-cm-diameter target. Subtended angles were 17.1 and 4.3 degrees for the large and small second-target conditions, respectively. Fifty trials per condition were performed, the last 3 of which were filmed at 120 Hz. The vertical dimension of movement (peak height along the z-axis) was captured directly from the camera view, whereas the horizontal (y-axis) dimension, that is, the dimension orthogonal to the principal direction of motion, was captured through a mirror positioned above the target board. Reaction times and movement times were significantly longer in the small second-target condition, thus replicating the well-known response complexity effect. Kinematic analyses revealed that when the subtended angle was smaller, there was significantly less horizontal pathway deviation as well as significantly higher peak vertical displacement in the movement. Therefore, the accuracy demands imposed by a smaller subtended angle do constrain the actual movement pathway.