Abstract
We quantified the accuracy of the perception of the absolute direction of motion in depth (MID) of a simulated approaching object using a passive judgment and an active simulated catching task. In contrast with previous research, our passive judgment task utilized a staircase tracking procedure that provided precise estimates of the perceived direction of MID and did not require the observer to make an interceptive motor response. For the active task, movements of the index finger and thumb of the observer's hand were tracked as participants tried to ‘catch’ the simulated approaching object (Gray & Sieffert, 2005). A sensation of MID was created using monocular and/or binocular information sources and visual stimuli were identical for both tasks. For the judgment task, observers overestimated the angular trajectory of the approaching object i.e., they judged the object to pass wider than the head than indicated by the visual information provided. When auditory feedback was added to the judgment task consistent overestimates were still observed. For the active task, observers consistently overreached i.e., the hand was further away from the midline than the simulated object at the time of hand closure. When auditory feedback was added to the active task errors were significantly reduced and were within the margin of error for successful catching. The relative accuracy in binocular and monocular conditions for individual observers could be partially explained by thresholds for unidirectional changes in angular size and changes in relative disparity. These findings suggest that adaptation of the motor component to the information provided by the visual system is the basis of successful interception.