Baseball hitting, binocular vision, and the Pulfrich phenomenon.
OBJECTIVES: To determine if dimming the light to 1 eye affects baseball hitting (motion-in-depth) and if binocular interaction influences the ability to hit a baseball. METHODS: The ability to hit baseballs in a batting cage was measured under conditions of (1) no filter before either eye, (2) neutral density filters before both eyes, and (3) a neutral density filter before 1 eye, while viewing with both eyes. Batting scores were based on the number of hits, fouls, and misses. RESULTS: A neutral density filter of 0.6 optical density before both eyes had no significant effect on batting ability compared with no filter (87% vs 94%). While viewing binocularly, a filter before 1 eye caused a significantly greater reduction in hitting scores than when the filter was placed before the opposite eye (36% vs 80%). This greater effect of 1 eye on hitting scores denotes an ocular preference or dominance within the motion stereopsis system. The eye associated with the greater reduction in hitting ability when dimmed by a filter was termed the dominant eye for motion stereopsis. In comparison with placing 0.6-optical density filters before both eyes, the same filter before the dominant eye reduced hitting ability (36% vs 87%), but when the filter was placed before the nondominant eye, the hitting ability was not significantly reduced (80% vs 87%). The batting scores decreased as filter densities increased from 0.3- to 0.6-optical density, and the effect was significantly more for the dominant eye than for the nondominant eye. CONCLUSIONS: Binocular vision contributes to the precise localization of a pitched baseball, and one eye influences baseball hitting more than the other eye. The motion-in-depth channel (baseball hitting) shares a sensitivity to unequal binocular illumination with the sideways-motion channel (Pulfrich phenomenon). The timing of the impulses conducted from the eyes appears to be critical for the precise localization of objects processed by either the motion-in-depth (baseball hitting) or the sideways-motion (Pulfrich phenomenon) channels.