WHOLE BODY REACHES ARE INFLUENCED BY GAZE DIRECTION AND TARGET ECCENTRICITY

Abstract

The effect of gaze signals in movement control is not well understood. There is evidence to suggest that reaching errors are biased toward gaze direction when stepping and reaching to remembered target locations. In contrast, reach errors were biased away from gaze direction when seated subjects reached to remembered eccentric (peripheral) targets. To better understand the eye-body movement interaction, tests were conducted to determine if whole body reaching errors were biased toward gaze was direction when the gaze was anchored elsewhere. PURPOSE: To examine the effects of gaze direction on three-dimensional whole body reaching movements. METHODS: Four healthy males and two healthy females were asked to step and reach to 5 different target locations: one central target 45 cm high, three targets at a height of 90 cm (one central, one 30° right, one 20°left) and one central target 147 cm high. All targets were located at a 95 cm radial distance from the trunk. Reaches occurred under four visual conditions: NORMAL, where there are no alterations in the visual field and subjects gaze at the target; VIRTUAL, where the target location is remembered and subjects gaze at the remembered target position; GAZE where an eccentric target location is viewed and remembered, while gaze position is anchored elsewhere; and GAZEe, which is similar to GAZE but the remembered target remains eccentric throughout the trial. For the central target at 90 cm (CENTER) the gaze was anchored at four different locations (GAZEe) and the GAZE condition was eliminated. Six reaches were made to each target in each condition. Lateral, vertical and anterior/posterior reaching errors were computed and compared across the visual conditions using a repeated measures ANOVA and Tukey's HSD post-hoc tests. RESULTS: For lateral targets, mean lateral reaching errors were biased toward the gaze anchor (mean range: 3–10 cm; p < 0.05). This trend was also seen for the CENTER target, but to a lesser extent (mean range: 1–3.5 cm). In contrast, in trials where the target was located at the largest eccentricity (in the vertical direction), vertical reaching errors were biased away from the gaze anchor (mean range: 15.5–16 cm for the CENTER target). CONCLUSION: These data suggest that whole body reaching movements are influenced by gaze direction; reaches are toward gaze for small target eccentricities and away from gaze for large target eccentricities. Grant support: NIH NS27484