a1 Intelligent Systems Laboratory, College of Engineering and the Department of Neurology, School of Medicine, Boston University
a2 Harvard-Massachusetts Institute of Technology, Division of Health Sciences and Technology
a3 Brigham and Women's Hospital, Harvard Medical school
a4 Smith Kettlewell Eye Research Institute
A series of psychophysical tests examining early and later aspects of image-motion processing were conducted in a patient with bilateral lesions involving the posterior visual pathways, affecting the lateral parietal-temporal-occipital cortex and the underlying white matter (as shown by magnetic resonance imaging studies and confirmed by neuro-ophthalmological and neuropsychological examinations). Visual acuity, form discrimination, color, and contrast-sensitivity discrimination were normal whereas spatial localization, line bisection, depth, and binocular stereopsis were severely impaired. Performance on early motion tasks was very poor. These include seeing coherent motion in random noise (Newsome & Paré, 1988), speed discrimination, and seeing two-dimensional form from relative speed of motion. However, on higher-order motion tasks the patient was able to identify actions from the evolving pattern of dots placed at the joints of a human actor (Johansson, 1973) as well as discriminating three-dimensional structure of a cylinder from motion in a dynamic random-dot field. The pattern of these results is at odds with the hypothesis that precise metrical comparison of early motion measurements is necessary for higher-order “structure from motion” tasks.
(Received April 17 1990)
(Accepted June 18 1990)
p1 Present address of Ken Nakayama: Department of Psychology, Harvard University, Cambridge, MA 02138.
Reprint requests to: Lucia M. Vaina, Intelligent Systems Laboratory, ERB-331, Boston University, 44 Cummington Street, Boston, MA 02215, USA.