Features versus spatial phase in a tachistoscopic laterality experiment.

Abstract

The abilities of the two hemispheres to instantly discriminate compound grating pairs with identical power spectra and the same separation in phase (180°) were compared in a tachistoscopic laterality experiment. Consistent with earlier observations by Fiorentini and Berardi (1984), a left-visual-field advantage was found for a stimulus pair differing in local contrast magnitude, whereas discrimination was not possible at all for a mirror-symmetric grating pair. This result contradicts the notion of a right-hemisphere advantage in processing spatial phase. Moreover, it is incompatible with the assumption that compound gratings are discriminated with respect to their Fourier components. This implies that discrimination must depend on the processing of local image components or features. Although the right-hemisphere advantage found is related to the analysis of local contrast variability within an image, the relative position of local image components is generally lost in extrafoveal vision.