The effect of observer-based and environment-based visual degradation on TTC estimation

Abstract

Often, we have to rely on limited information when judging time-to-contact (TTC), as for example, when driving in foul weather. The visual stimulus can be degraded for such environment-based external reasons. Or it can be degraded for observer-based internal reasons, as in situations where we would need reading glasses but do not have them handy. Most existing studies on the ability to judge TTC have worked with optimal visual stimuli. We explored to what extent TTC estimation is affected by external or internal stimulus degradation. A simple computer-simulated object approached the observer at constant speed. It was occluded after 1 or 1.5 s. The observers pressed a button when they thought the object would have collided with them (prediction motion paradigm). We found that dioptric blur and simulated snowfall shortened TTC-estimates. Contrast reduction led to overestimated TTC estimates, which could be the result of distance overestimation or speed underestimation of low-contrast objects. Our findings suggest that vision impairments have adverse effects on TTC estimation, depending on the type of degradation (internal vs. external) and the accompanied changes of visual cues provided in the environment.