Academic journal article Research Quarterly for Exercise and Sport

Object Rotation Effects on the Timing of a Hitting Action

Academic journal article Research Quarterly for Exercise and Sport

Object Rotation Effects on the Timing of a Hitting Action

Article excerpt

We investigated how perturbing optical information affects the guidance of an unfolding hitting action. Using monocular and binocular vision, six participants were required to hit a rectangular foam object, released from two different heights, under four different approach conditions, two with object rotation (to perturb the viewed surface area) and two without. Participants made more misses under monocular conditions, and the presence of rotation had a significant effect on the duration between the arm's peak velocity and its contact with the object. We conclude that binocular information contributes to the timing of interceptive tasks. In addition, the guidance of interceptive actions does not appear to be based solely on object expansion information picked up from the viewed surface area.

Key words: binocular, monocular, time-to-contact, tau

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Many real-world interceptive tasks require the performer to carry them out under fine spatiotemporal constraints. The role that optical information plays in satisfying these constraints has received a large amount of research attention. The visual angle subtended at the eye by the object to be intercepted has played a key role in explaning how interceptive acts could be regulated. For example, Lee (1976) demonstrated that the relative expansion rate of the visually subtended angle of an approaching object could, in principle, specify the remaining time-to-contact between an observer and an approaching object. Lee termed this optic variable as "tau," which was initially expressed as the angle subtended by the object at the eye divided by the subtended angle's rate of change.

Most of the research into tau and the regulation of interceptive tasks in general has focused on situations in which the object to be intercepted expands isotropically (e.g., Lee, Young, Reddish, Lough, & Clayton, 1983; Michaels, Zeinstra, & Oudejans, 2001). Under isotropic conditions, the viewed surface of the approaching object expands in a uniform manner. A nonisotropic expansion occurs when parts of the viewed surface area do not expand at the same rate. The rotation of an irregular shaped object as it approaches could result in a nonisotropic expansion. Gray and Regan (1999) identified a tumbling rugby ball or American football as examples. However, many everyday interceptive tasks are performed in nonisotropic expansion conditions, for example, traffic merging at a roundabout would provide a nonisotropic approach (Gray & Regan, 1999). There has been a limited amount of research into what sources of information are used in nonisotropic expansions (Gray & Regan, 2000; Kaiser & Hecht, 1995; Scott, Li & Davids, 1996).

Scott et al. (1996) examined participants' timing and performance when they were required to physically intercept falling objects that approached with a nonisotropic expansion. Participants were required to strike the object as hard as possible with a straight arm. The objects approached under one of four conditions, namely, a nonrotating spherical ball, a nonrotating oval ball dropped point first, a nonrotating oval ball dropped sideways, and a rotating (1.5 rotations [s.sup.-1]) oval ball in which the rotation caused the image size to reduce initially. Therefore, the first three conditions resulted in the approaching objects having isotropic expansions, and the fourth condition resulted in a non isotropic expansion. Participants viewed all conditions with binocular vision. With regard to performance, participants were successful in striking the ball in all trials. In relation to the timing, the average movement initiation time (the time period between ball release and first movement) was similar for the first three conditions. In Condition 4 the average movement initiation time was 30 ms later than the other conditions. These findings suggest that viewing the surface area of the ball may contribute to picking up timing information. …

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