When intercepting an approaching ball in flight, only some individuals compensate for its acceleration through head-centered spherical space.

Abstract

An attempt to catch a ball must be preceded by accurate visual tracking while, as a result of the ball’s changing depth, it accelerates through the head-centered, spherical frame of reference (described in degrees azimuth/elevation). However, studies of smooth pursuit of 2D fronto-parallel motion demonstrate a perceptual insensitivity to acceleration. This predicts that gaze will lag behind an accelerating target. In the natural context, one might couple rotation of the gaze-vector to a visual source of information that covaries with changes in depth. This study tests the potential role of information related to angular size. Subjects were immersed in a virtual reality ball catching simulation, and gaze was monitored using an integrated eye tracker. The ball travelled to one of three lateral distances from the subject’s head. Arrival height was randomized. A gain was applied to the ball’s natural looming rate resulting in inflation/deflation of the approaching virtual ball. Subjects performed 10 repetitions at gain values of 0.5, 0.75, 1 (normal looming rate), 1.25, and 1.5. Ten repetitions of each gain/distance combination yielded 150 trials per subject. Although the preliminary analysis presented at VSS2018 supported the role of looming rate in compensation for the ball’s acceleration, a new, more sensitive analysis casts doubt on these findings. On each trial, tracking behavior was compared to ball movement during a windowed portion of the ball’s trajectory through head-centered spherical space, just prior to the attempted catch, during which the trajectory was linear and subject to acceleration. Comparison between the location of gaze at the end of the window to 1) the actual ball location at the end of the window and 2) the location predicted by a constant-velocity model of ball movement revealed two distinct classes of participant – those that partially compensated for acceleration, and those who did not.