Spatial, temporal and chromatic properties of human scalp-recorded potentials evoked by patterned visual stimuli

Abstract

A series of experiments are reported in which the spatial, temporal and chromatic properties of the initial components Cl and CII of the transient pattern-onset VEP, of predicted striate and extrastriate origin, are examined. Where relevant the response properties of these components are compared with those of single units in the mammalian visual system and with psychophysical data in man obtained under comparable stimulus paradigms.
In chapters 3 to 5 the time course of temporal summation of Cl and CII for single time varying stimuli of variable contrast are examined. The time course of temporal summation and the interval for complete temporal resolution of Cl for brief discrete pairs of patterned stimuli of the same or opposite polarity has also been studied, and the data related to psychophysical phenomena. The results of the experiments in chapter 6 suggest that high frequency VEPs elicited by patterned stimuli are generated by the same region of visual cortex as that of the Cl component of the transient pattern-onset VEP.
The experiments of chapter 7 to 9 were designed to seek electrophysiological correlates of the psychophysically identified 'sustained' and 'transient' visual processing channels, and of various types of pattern masking phenomena which have been postualted to be the result of neuronal interactions between these channels.
In chapter 10 an adaptation paradigm is used in conjunction with grating and regular dot patterns, to seek electrophysiological evidence for 'length' and 'non-length' selective channels which have been postulated on the basis of psychophysical data.
The results of experiments reported in chapter 11 show that both Cl and CII are sensitive to patterns of isoluminant colour contrast; a finding consistent with single unit data from monkey, and suggesting that many cells within the human visual cortex signal both luminance and colour contrast. The scalp distribution of these colour and luminance contrast VEPs are compared in detail in chapter 12.
In chapter 13 further stimulus specificities of the Cl component are investigated.