The double step analysis of rapid manual aiming movements

The present paper examines the control principles underlying rapid manual tracking responses to horizontal double-step stimuli. The paper reports an experiment concerned with responses made to step-stimuli presented in quick succession. The amplitude of the second-step was varied between the initial step-position and the home-base. Double-step response parameters were analysed as a function of the determinant time interval (D) between the second step and the onset of the initial response. The initial response amplitude was observed to vary as a function of D. Amplitude transition functions were constructed representing the transition of the initial response amplitude between the two step positions; their slopes, furthermore, depended on the amplitude of the second target step. No delays in the initial reaction time with the interstimulus interval were observed. Minor delays to the onset of a corrective response were observed. These delays were in part related to a movement time constraint that is independent of any limitations in central processing capacity. The present findings for the manual control system are compared to double-step tracking analyses of the oculomotor control system.