Ocular pursuit and the estimation of time-to-contact with accelerating objects in prediction motion are controlled independently based on first-order estimates

The present study examined for the first time both the ocular and manual responses in a prediction motion (PM) task requiring participants to estimate time-to-contact (TTC) of an accelerating object. Results showed that while the ocular response initially matched well the object motion, smooth pursuit decayed towards zero following object occlusion, during which participants exhibited a saccadic response that placed the eyes in the region of the point of contact. The primary saccade was completed in advance of the object reaching the point of contact, and was best predicted by a first-order estimate of TTC (TTC1). Participants then made their manual response, which was also best predicted by TTC1. Therefore, object acceleration was not taken into account in either the ocular or manual response, with the latter occurring before the object reached the point of contact when it decelerated and after when it accelerated. Further analyses of the ocular and manual responses indicated no functional relationship and independent control. We suggest that the demand to make temporal estimates with a stationary location in PM tasks is critical in explaining the discrepancy with oculomotor research.