Abstract
A number of researchers have demonstrated that retinal motion signals influence goal-directed reaches in the direction of the observed motion: a behavioral phenomenon referred to as the manual following response (MFR). In the present study, we sought to determine if retinal motion cues influence online reaching control as well as determine if target eccentricities influence the MFR. Participants completed mediolateral reaches to briefly presented (i.e., 150 ms) targets (eccentricities: 10.2 and 19.5 cm) within a stationary, left or rightward moving (50°/s) random dot kinematogram. Target onset served as the movement imperative cue and occurred in time with activation of background motion. Results indicated that reaction times increased with increasing target eccentricity; however, the different background motion conditions did not modulate this effect. In addition, left and right background motion cues elicited a reliable MFR, but only for the 19.5 cm target eccentricity. Notably, detailed analyses of reach trajectories indicated that the observed MFR could not be attributed to differences in the online control of the movement. Thus, our results suggest that retinal motion signals require some minimum time to be incorporated into a response and/or that a critical movement amplitude is required to elicit the MFR. Moreover, our results provide the first direct evidence that the elicitation of the MFR is not attributed to putative differences in online control.
