Long-lasting, long-range detection facilitation

We examined the time course of threshold reduction in the Gabor lateral masking paradigm. Contrast detection thresholds were measured (2AFC) for a briefly presented (36 ms) foveal Gabor signal (GS), preceded by a presentation (90 ms) of two high-contrast GS flanked masks, with stimulus onset asynchrony (SOA) varying from 0 to 16,290 ms. Using target-to-mask separations of 3 lambda and 12 lambda (lambda = 0.15 degree, GS wavelength), the 3 lambda separated GS masks enhanced target threshold by 0.25 log units at SOA = 0 and by 0.17 log units at 2700 ms. At 12 lambda separation, threshold was enhanced by 0.11 log units at SOA = 0 and by 0.14 log units at 2700 ms. Long-range (12 lambda) and short-range (3 lambda) enhancements persisted for over 16 s. Delayed and simultaneous enhancement depended on the stimulus configuration (maximal for collinear target and masks), local parameters (orientation, spatial frequency and phase), and the presented eye (dichoptic versus monoptic). The results suggest that spatial filters in early vision retain an input trace far beyond the perceptual integration range. This trace may subserve the consolidation of filter activity into long-term memory.