IN a previous paper (van Balen and Henkes, 1960) we indicated the possibility of recording the response of the occipital lobe to light-stimulation in man. The use of Dawson's superimposition method together with the mathematical integration method enabled us to record the responses in all normal subjects.The specific response of the visual cortex consists of four different components: a small surface-positive wave a, followed by a somewhat larger negative wave b, then by the main positive deflection c and a smaller negative deflection d (van Balen and Henkes, 1960, Fig. 5). The positive deflection c consists of two components: cl and c2. A study of the specific response to light stimulation of varying intensities and at different levels of dark adaptation revealed the correspondence of the amplitude of the cl-wave with the level of activity of the photopic mechanism, and of the amplitude of the c2-wave with the level of activity of the scotopic mechanism.The photopic and scotopic mechanisms, however, are concepts of the physiology of the retina and coincide more or less with the anatomical concepts of cones and rods.In the ganglion cell layer of the retina a regrouping occurs. Foveal cones in monosynaptic units form the foveal system; peripheral cones and rods in polysynaptic units form the extra-foveal system. Anatomically the foveal and extra-foveal systems can be distinguished in all parts of the visual system. In the visual cortex (striate area), for instance, a foveal (" macular") and extrafoveal ("extra-macular") projection field can be distinguished. These data lead one to expect the separate representation of the foveal and extra-foveal systems in the occipital response.
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