Psychophysically, the visibility of a small foveally viewed Gabor patch can either be enhanced or suppressed by laterally placed Gabor patches of similar orientation and spatial frequency. The sign of the effect, enhancement or suppression, depends on target and flank separation and on the relative orientation of the target and its flanks. Maximal threshold enhancement occurs for co-oriented, collinear targets that are separated by several wavelengths of the spatial frequency of the Gabor patches. The changes in contrast threshold, relative to a standard (no mask) condition is plotted in Figure 1 as a function of target to mask distance (in units of target wavelength). Two zones, suppression and facilitation, where contrast detection thresholds are affected by flanking Gabor maskers were observed. The suppression region, within an eccentricity of , contrast detection thresholds increased up to factor of two. Outside this region detection thresholds are reduced up to factor of two, resulting in a facilitatory region extended up to . Maximum facilitation found at and progressively returning to the standard threshold by . Assuming a filter size of about 2 wavelengths (e.g. ), facilitatory effects occurred over distances spanning several receptive fields. Suppression had a much shorter spatial range and presumably was due to interactions from nearby filters .
Figure 1: Dependence of target perceptual threshold on target to mask distance. Threshold elevation is computed relative to that of an isolated target. Data is presented for a collinear configuration of target and masks (). Similar functions are found for different target and mask spatial frequencies.