Stimulus-response compatibility in a small sample of cerebral palsied adults

Stimulus-response compatibility refers to the correspondence between a sensory event and the motor response which it specifies. A discrete aimed movement task with two conditions of stimulus-response compatibility tested whether higher compatibility would decrease the reaction time of 5 subjects with normal movement and 6 subjects with cerebral palsy. A board with 3 distances (13.5, 28.0, 40.5 cm) along each of 3 rays (45 degrees, 90 degrees, 135 degrees) provided 9 target sites for a detachable leaf switch. A light on the switch was turned off or on for the low or high compatibility condition. The independent variables were the Index of Difficulty, target position and compatibility. The dependent variables were reaction time and movement time. The reaction times for both groups were less during the high compatibility condition than during the low compatibility condition as shown by a t test for differences between means. Multiple regression analyses showed that reaction time of the normal group was a positive linear function of compatibility and movement time was a positive linear function of the Index of Difficulty for both groups and of position for the normal group, 3 normal subjects and 2 cerebral palsied subjects. There were indications of ballistic rather than aimed movements. The results are discussed with regard to the role of visual fixation in aimed movement, the similarities between groups in conformance to Fitts' Law and differences between groups in reaction and movement times.