Left hand, but not right hand, reaching is sensitive to visual context

Abstract

Recently, it has been reported that grasping with the left hand is more vulnerable to visual size illusions than grasping with the right hand. The present study investigated whether this increased sensitivity of the left hand for visual context extends to reaching. Left- and right-handed participants reached for targets embedded in two different visual contexts with either left or right hands. Visual context was manipulated by presenting targets either in a blank field or within an array of placeholders marking possible target locations. Regardless of handedness, the presence of placeholders affected left hand, but not right hand, reaching by improving end-point accuracy and reducing movement speed. Furthermore, left hand reaching was more accurate for far than near targets, whereas right hand reaching showed the opposite pattern. We discuss two possible hemispheric lateralization accounts of these findings.

Fig. 1

Schematic overview of the start, target and body positions for movements with the right and left hand. Participants executed rapid hand movements from the start box to one of the seven target boxes (each 10 × 10 mm, separated by 5 mm) with either the other boxes present (placeholder condition) or the other boxes absent (no-placeholder condition). The distance between the start box and first target box was 90 mm (side-to-side). The seven target locations were at increasing distances from the start location (i.e., 100, 115, 130, 145, 160, 175, and 190 mm)

Fig. 2

Mean performance indices for left and right hand reaching movements as a function of target position and placeholder condition: (a, b) movement time (ms) (c, d) absolute error (mm) (e, f) constant error (mm). Note, for constant error, negative values reflect undershoots, positive values reflect overshoots relative to the target’s midpoint in the principal direction of motion