Attention and Amblyopia an Electro-Encephalographic Approach to an Ophthalmological Problem

Abstract

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.

Visual evoked retinal and occipital potentials

“…The majority of evidence favors the likelyhood that the abnormality in amblyopia is located at cortical levels, HENDERSON (1962). Recently in a study of evoked occipital potentials, VAN BALEN & HENKES (1962) have suggested that amblyopia due to squint results from inattention and consequent lack of activation of the foveal system.…”

Photically Evoked Potentials (PEPs) in Brain Disorders

“…However, in man, a number of problems still remain unsettled, although many equipments to detect the evoked potentials are designed and the configuration of evoked potentials is analysed by many investigators. Concerning photically evoked potentials (PEPs), Cobb and Dawson,1) Monnier,2,3) Ciganek4) and others [5][6][7][8][9][10] reported the configuration in detail , but their results are not in agreement.…”

Influence of Central Depressant Drugs on Pupil Function: An Evaluation with the Pupil Cycle Induction Test

“…Visual-evoked potentials studies have shown evidence of the influence of attention on evoked response pattern [17]. When the subject has been instructed to look at the stimulus with attention, the stimulus elicits an early negative component in occip ital visual-evoked response [18].…”