Holmes NP, Plainis S, Murray IJ (2000) Hemispheric asymmetries in perceptual-motor processing and the 'Space-Ship Plot': Simple reaction time to lateralised sinusoidal gratings. BSc Thesis, University of Manchester, 42pp.
Simple reaction time (RT) to sinusoidal gratings varying in contrast, spatial frequency and luminance was measured for brief stimuli presented at different eccentricities in both visual fields of two young subjects. Over a range of contrasts, RT increased in proportion to the reciprocal of contrast. With increasing eccentricity and spatial frequency, the slope and constant of the hyperbolic RT-contrast curve increased. With decreases in luminance, the constant but not the slope increased. The linear relationship between RT and the reciprocal of contrast held for all spatial and luminance stimulus-characteristics. One subject showed no consistent trend towards lateralisation of processing as a function of stimulus characteristics. The other subject showed a consistent and highly significant left visual field / right hemisphere advantage (13 to 19 ms) over all stimulus conditions. Control experiments for one subject indicated a highly significant left versus right foot advantage, and an 80 ms advantage for hand over foot responses. A linear coefficient relating the RT to the reciprocal of contrast was calculated for all stimulus conditions, and plot on a single graph for each subject. The slope coefficient varied monotonically as a function of eccentricity for high luminance stimuli at all spatial frequencies. The slope coefficient was constant for scotopic luminance conditions. Aspects of this ‘Space-Ship’ plot were related to electrophysiological and neuroanatomical characteristics of the visual input pathways. The RT-1/contrast slope coefficient predicts contrast gain and contrast sensitivity in single unit primate studies. For this reason, the slope coefficient is suggested as a superior alternative to absolute RT data, in assessing the hemispheric-asymmetrical processing of sinusoidal gratings in the simple reaction time paradigm