Differential spatial displacement discrimination thresholds for Gabor patches.

Differential spatial displacement discrimination thresholds were determined for a configuration of three identical Gaussian modulated patches of sinusoidal grating presented with equal orientation and at threshold luminance contrast. The patches were arranged one above the other at equal spatial intervals. The orientation of the bars of the sinusoidal grid constituting the patches was orthogonal to the axis joining the centres of the outer two patches. Thresholds were determined for displacements of the middle patch both orthogonal to and along the axis joining the outer two patches. Thresholds for both tasks were obtained as a function of both the spatial frequency of the sinusoidal grating and the spatial scale parameter of the Gaussian envelope of the patches. We found that the differential spatial displacement discrimination thresholds for both tasks are a constant fraction of the spatial scale parameter of the Gaussian envelope of the sinusoidal grating patches and are independent of the spatial frequency of the modulated grating. We conclude that the human visual system is capable of assigning a single location tag to an entire Gaussian modulated patch of sinusoidal grating. The accuracy with which the relative position of such a Gabor patch can be determined in a constant fraction of its spatial extent (spread of the Gaussian spatial envelope).