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Holmes NP, Plainis S, Murray IJ (2001) The space-man cometh. Or: Simple visual reaction time to lateralised sinusoidal gratings. Experimental Psychology Society, Manchester, UK, 12th July    
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Abstract
The visual input system of the brain possesses a centre-surround receptive field organisation incorporating lateral inhibition. Consequently, cells in the retino-thalamo-striate pathway strongly respond to stimuli varying sinusoidally in the frontal plane. Due to the left-right anatomical hemispheric symmetry of these pathways, researchers have assumed that functional hemispheric asymmetries for the processing of simple sinusoidal stimuli would not be found. Indeed, only minor hemispheric asymmetries in Simple Reaction Time (SRT) studies have been reported, but in all cases, only a limited number and range of stimuli were used. There is cause, therefore, to examine hemispheric asymmetries over a much wider range of stimulus variables in a SRT paradigm, to confirm the absence of functional asymmetry, and further to examine the inter-relationship of stimulus variables with respect to neuroanatomical and neurophysiological properties of visual input pathways. The present study varies the contrast (10 levels), spatial frequency (3 levels), luminance (3 levels), and eccentricity (4 levels) of sinusoidal grating stimuli presented in both visual fields of two subjects, and derives a linear coefficient relating contrast level and SRT. This linear factor correlates well with anatomical and physiological properties of visual input pathways in man and other animals, and offers distinct advantages over using raw SRT data. When this factor is plot against eccentricity for different spatial frequencies and luminances, a 'Space-Ship’ plot emerges which reflects further pathway properties. Perceptual-motor hemispheric asymmetries, inter-stimulus, and inter-subject variability were found for raw SRT data, but not for the derived linear factor, supporting the assertion that this second-order measure better reflects early visual processing