Time-to-contact: More than Tau alone

Two time-to-contact (T-c) experiments are reported that manipulated the manner in which a visually simulated target vehicle disappeared from the screen. In both experiments, one condition featured the traditional, spontaneous disappearance of the vehicle. A contrasting condition featured the occlusion of the vehicle behind a natural object. The available visual information was essentially equivalent in each condition. If T-c is specified by information in the expanding optic array alone, the two conditions should produce equivalent estimates of T-c Results of each experiment, however, showed estimates with 14% and 12% greater accuracy in the occlusion condition compared to the disappearance condition. This implies that T-c judgments depend on more than the rate of optical expansion. In addition to the occlusion manipulation, factors influencing the accuracy of T-c estimates included both the sex and age of the participant. In an effort to compare T-c estimates with time-judgment ability, participants also performed a time-production task with the same temporal structure as the T-c task but with no graphic scene representation. A positive relation was found but further clarification is still needed between these two capabilities.