TIME-TO-CONTACT - MORE THAN TAU ALONE

Two time-to-contact (T-c) experiments are reported that manipulated th e manner in which a visually simulated target vehicle disappeared from the screen. In both experiments, one condition featured the tradition al, spontaneous disappearance of the vehicle. A contrasting condition featured the occlusion of the vehicle behind a natural object. The ava ilable visual information was essentially equivalent in each condition . If T-c is specified by information in the expanding optic array alon e, the two conditions should produce equivalent estimates of T-c Resul ts of each experiment, however, showed estimates with 14% and 12% grea ter accuracy in the occlusion condition compared to the disappearance condition. This implies that T-c judgments depend on more than the rat e of optical expansion. In addition to the occlusion manipulation, fac tors influencing the accuracy of T-c estimates included both the sex a nd age of the participant. In an effort to compare T-c estimates with time-judgment ability, participants also performed a time-production t ask with the same temporal structure as the T-c task but with no graph ic scene representation. A positive relation was found but further cla rification is still needed between these two capabilities.