CONTOUR INTERACTION IN THE PRESENCE OF CONGENITAL NYSTAGMUS

Using a computer-generated acuity task, the resolution of vertical and horizontal Landolt Cs was assessed at three levels of contrast, each for three different crowding conditions, Eighteen adults participated; six had congenital idiopathic nystagmus, six were oculocutaneous albi nos and six served as controls, Contour interaction was evident when b ars were placed 1 gap-width from the Landolt C and was more marked as contrast increased, When scaled to the individual resolution limit, th e magnitude of contour interaction displayed by the albinos was not si gnificantly different from the controls, however the idiopaths did exh ibit a greater crowding effect than the controls, These results imply that fixation instability is a contributory factor in contour interact ion, but only when retinal image velocity is above a certain threshold .