The Effect of Early Anomalous Visual Inputs on Orientation Selectivity

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Abstract
It is now well established that the cortical neurones of cats and monkeys respond best to either lines or edges of a specific orientation. The respective tuning curves of these cells can be broadened by rearing the animals in abnormal visual environments during their critical period of development. Since neurones in the human visual system probably also possess this orientational selectivity, then it is not inconceivable that humans also could demonstrate similar orientational selectivity loss if they too have an anomalous visual input during their early years of life. To test this hypothesis, a simultaneous subthreshold masking technique is proposed as a means for assessing psychophysically the selectivity properties within the human striate cortex. Both visually normal and abnormal systems were considered. No selectivity loss is demonstrated for either the orientationally deprived (i.e. high astigmats) or monocular form deprived (high anisometrope) subjects. The effect of large eye movements (nystagmus) does, however, bring about a coarser selectivity. These results are discussed in relation to recent neurophysiological studies of the critical period in lower vertebrates.