LATERAL INTERACTIONS BETWEEN SPATIAL CHANNELS - SUPPRESSION AND FACILITATION REVEALED BY LATERAL MASKING EXPERIMENTS

We measured contrast detection thresholds for a foveal Gabor signal flanked by two high contrast Gabor signals. The spatially localized target and masks enabled investigation of space dependent lateral interactions between foveal and neighboring spatial channels. Our data show a suppressive region extending to a radius of two wavelengths, in which the presence of the masking signals have the effect of increasing target threshold. Beyond this range a much larger facilitatory region (up to a distance of ten wavelengths) is indicated, in which contrast thresholds were found to decrease by up to a factor of two. The interactions between the foveal target and the flanking Gabor signals are spatial-frequency and orientation specific in both regions, but less specific in the suppression region.