Target Contrast Affects Reaching and Grasping in the Visually Impaired Subjects

Abstract

The aim of this study is to investigate whether subjects with central visual impairment (VI) show different reaching and grasping behavior for targets of different contrasts compared with visually normal age-matched subjects. Reaching and grasping performance was measured in 14 subjects with VI and 14 normal subjects. Subjects were asked to pick up a cylindrical target. Three different targets were used: black (low contrast), white (high contrast), and transparent, placed against a black background. A motion analysis system (Vicon 460) recorded and reconstructed the hand and finger movements. Significantly longer onset times, total movement duration, and time after maximum grip aperture were obtained for subjects with VI compared with normal subjects (p < 0.002). No significant differences existed in maximum velocity and grip aperture between the two groups for any of the targets. Subjects with VI took longer to initiate and to complete the movement. Maximum velocity and grip aperture were not different suggesting that once the target was "seen" by subjects with VI performance was similar to normal subjects. Time after maximum grip aperture was longer in subjects with VI indicating the need for "online" modifications in these subjects. Contrast sensitivity was significantly correlated to more indices than visual acuity.