Influence of Approach Angle on Estimates of Time-To-Contact

Abstract

Is the retinal periphery as capable of extracting time-to-contact information from a radially expanding optical flow field pattern as the retinal center? To address this proposition, two experiments were performed using both male and female participants viewing graphically generated scenes that depicted one road approaching directly towar them and a second road approaching from a 40 deg. angle to their left. A vehicle could approach the observer along either road and was removed at various times before contact. Participants were required to estimate when the vehicle would have reached their position. Each experiment employed a 2 by 2 by 3 design in which sex was a between-subject variable while vehicle approach trajectory and either vehicle removal distance or vehicle approach velocity were within-subject variables. Results of the experiments indicate the retinal periphery is less sensitive to time-to-contact information than the retinal center. Variations in estimates of time-to.contact increased with vehicle removal distance and vehicle approach velocity while the accuracy of time-to-contact estimates increased with viewing time. In addition, withonly a single approach velocity, the first experiment yielded no significant sex differences. How- ever, when vehicle approach velocity was manipulated, significant sex differences emerged. The theoretical and practical ramifications of these results are presented.