THE SOURCE OF DISPARITY VERGENCE INNERVATION DETERMINES PRISM ADAPTATION

A physiological model of prism adaptation argues that adaptation magni tude and rate are functions of the magnitude of reflex vergence innerv ation. It has also been shown that there is reduced prism adaptation m agnitude for a given disparity stimulus where only peripheral sensory fusion is present (the 'eccentricity effect'). This study attempted to determine whether the eccentricity effect is attributable to reduced reflex vergence innervation in peripheral fusion. Experiments were run in a Maxwellian View haploscope: Convergence and divergence adaptatio n to 6 Delta disparity stimuli were quantified for seven binocularly n ormal subjects using subjective heterophoria measurements. Vergence re sponse during central or peripheral fusion was quantified objectively by infrared oculography. Six of seven subjects revealed an eccentricit y effect. However, in three of seven subjects the eccentricity effect was not predictable from the manifest vergence response. The results s uggest that the source of reflex vergence innervation affects prism ad aptation. A model is proposed whereby different sources of reflex disp arity vergence innervation stimulate prism adaptation by way of separa te neurological pathways of differing responsiveness.