Vision For Guidance And Vision For Feedback: A Study Of Throwing

Visually-directed throwing (i.e., throwing blindfolded after previewing a target location) is known to be more variable than visually-guided (normal) throwing. Here we explore the roles of visual guidance during the throwing action and of visual feedback gained by seeing the outcome of the throw. Varsity basketball players (Division III athletes: 8 F; 14 M) and other students (25 F; 17 M) performed 120 throws to a projected target from a distance of 4 m. LCD shutter goggles were used to block vision either immediately after the release of the ball (allowing visual guidance, but denying feedback) or during the period leading up to the release (denying visual guidance, but allowing visual feedback). Alternating blocks of 10 trials in each condition were used, with the first 40 trials excluded as practice. Both aim (deviations left and right) and distance calibration (deviations in depth) were analyzed for the remaining 40 trials in each condition. Athletes had better aim (lower variance in performance) with visual guidance than with visual feedback, t(21) = 5.04, p \u3c .001 but non-athletes showed no differences in aim between the two conditions and were worse overall than the athletes. Both athletes and non-athletes tended to slightly underthrow with feedback, but tended to show improvement over the course of each set of 10 feedback trials. However, both groups seemed to overcompensate when feedback was withdrawn, overthrowing by several centimeters on average. We conclude that both visual guidance and visual feedback are important factors in the control of throwing, with guidance primarily providing stabilization of aim in skilled throwers, and visual feedback providing force calibration