Abstract
Our ability to estimate the time-to-contact (TTC) of objects has often been studied using predictive motion tasks. In these tasks, an object moves for an initial period before it is occluded, and the participants must judge when they expect the object to reach a specified location. The target can either disappear behind a visible or invisible occluder (i.e., the moving object suddenly disappears). A key difference is that when the occluder is visible, participants know how long they can accumulate visual information for and update predictions about the object´s trajectory until then. When the occluder is invisible, one cannot benefit from this additional information. In this study, we looked at whether differences in occluder visibility led to differences in the accuracy and precision of TTC estimations by asking participants (N=12) to press a key when they thought a moving target was aligned with a vertical line presented on the right side of a screen. Targets were 1 cm white disks that moved rightwards at either 5, 10 or 15 cm/s, and were visible for 150, 300, 600 or 1200 ms, and occluded for the rest of their trajectory. The occluders were randomly presented as either white or invisible rectangles. In both cases, the occlusion periods were 100, 200, 400, 800 or 1600 ms. Results indicate that participants systematically overestimated the targets´ TTC. Yet, seeing the occluder led to more accurate and precise responses. Increased occlusion time decreased accuracy, while the amount of time the target was seen prior to occlusion did not influence performance. These results suggest that seeing the occluder and anticipating when the target will disappear allows participants to adopt strategies that facilitate predictions of the object’s TTC.