THE ARCHITECTURE OF PERCEPTUAL SPATIAL INTERACTIONS

Lateral interactions between spatial filters were explored with a late ral masking paradigm. Contrast sensitivity (two-alternative forced-cho ice) for a Gabor signal in the presence of two flanking high contrast Gabor signals (masks) was measured. When the target to mask distance w as less than 2 target wavelengths the contrast sensitivity decreased u p to a factor of two relative to a no mask condition. At larger separa tions, up to eight wavelengths, an increase in contrast sensitivity oc curred. This increase was maximal at separation distances of 2-3 wavel engths, where sensitivity increased by a factor of two. However, the e nhancement magnitude and range was dependent on the offset between the Gabor signal orientation and the direction defined by the virtual lin e connecting the two masks (global orientation). Maximal effects occur red when this offset was zero (100% increase in sensitivity) and 90 de g (50% increase). A 45 deg offset yielded only a small enhancement (20 %). The enhancement dependence on spatial arrangement was found to be invariant across different global orientations (meridian). This patter n of interactions may be involved in grouping collinear line segments into smooth curves.