The Physiological Basis of Simultaneous Contrast in the Retina

Abstract

The loci of contrast effects in the visual system have been a subject of controversies in the literature of vision. Among others, Helmholtz (9) was firm in his opinion that simultaneous contrast depends on “judgment”. Hering (10) assigned the phenomena of contrast to a physiological rather than to a psychological mechanism. Sherrington’s classical experiments (26, 27) made with rotating discs may be interpreted as indicating that the physiological processes for contrast occur at a lower level of the nervous system than that required for binocular fusion. Brückner (4) found that in clinical cases with injury above the level of the lateral geniculate, color contrast could be induced into the injured half of the visual system by stimulation of the other half. In his studies on ‚retinal induction‛ measured with electrical phosphenes as an index, Motokawa (14) suggested the peripheral nature of this phenomenon on the basis of the findings obtained from cases of homonymous hemianopsia. Kohata (12) showed that ‚retinal induction‛ was abolished by a mechanical pressure as small as 50 g applied to the eyeball, while the photosensitivity of the eye was almost unaffected by such a slight pressure. All these phenomena suggest the retinal origin of ‚retinal induction‛. It was, however, demonstrated by Motokawa, Komatsu and Watanabe (16) that ‚retinal induction‛ could be induced from the contralateral eye. This phenomenon together with the well-known phenomena of binocular contrast necessitates some central mechanisms.

From the Department of Physiology, Tohoku University, Sendai, Japan.