Orientational anisotropy in the human visual system

Abstract

A global pattern/randomness threshold was used to investigate orientational anisotropy in the human visual system. Dynamic transpositionally symmetric textures were used, since they allowed the investigation of three theoretically derived variables, size, orientational uniformity, and numerosity, independently and in interaction. The detectability of correlation, as indexed by these thresholds, was found to be dependent on the size of the uniform point-pair elements, Δd, and their orientation; larger tolerable Δd values were found in the vertical meridian. Increasing the stimulus field size increased the absolute value of this threshold, but not the relative value as a function of orientation. The thresholds were also found to be dependent on the orientational uniformity of the point-pairs. Tolerable perturbation did not vary as a function of the uniform orientation until a critical point-pair size was exceeded. This critical point-pair size did vary as a function of orientation, falling quite distinctly from vertical, to horizontal, to oblique. The number of point-pair elements comprising the textures did not affect the global pattern/randomness threshold. The implications of these data for the neural mechanisms underlying the "oblique effect" were examined, and it was concluded that an orientational anisotropy might exist in the length of receptive fields serving functional units selectively sensitive to orientation. It was also concluded, however, that this factor alone could not account for the various examples of the orientational anisotropy in vision, and that any anisotropy measured in human vision might be the net product of more than one anisotropy existing within and between the various levels of processing in the human visual system. © 1985 Psychonomic Society, Inc.