PERCEPTUAL-DISTORTION CONTRIBUTES TO THE CURVATURE OF HUMAN REACHING MOVEMENTS

Unconstrained point-to-point human arm movements are generally gently curved, a fact which has been used to assess the validity of models of trajectory formation. In this study we examined the relationship betw een curvature perception and movement curvature for planar sagittal an d transverse arm movements. We found a significant correlation (P < 0. 0001, n = 16) between the curvature perceived as straight and the curv ature of actual arm movements. We suggest that subjects try to make st raight-line movements, but that actual movements are curved because vi sual perceptual distortion makes the movements appear to be straighter than they really are. We conclude that perceptual distortion of curva ture contributes to the curvature seen in human point-to-point arm mov ements and that this must be taken into account in the assessment of m odels of trajectory formation.