Contour erasure affects the contrast threshold for grating targets

Brief adaptation to a flickering outline of an object’s contour leads to its disappearance, which is referred to as contour erasure. Previous studies showed that contour erasure increased the contrast thresholds to targets with a homogeneous luminance contrast. Here, we used radial and concentric sinusoidal gratings as stimuli to investigate how contour erasure affects the detection of luminance modulation patterns, and how it interacts with lateral modulation. The target was a concentric grating with a crescent-shaped window (2-degree width and 2- to 8-degree length). The background patterns were concentric or radial gratings containing two blank regions (i.e., simulated scotomata) on the left and right of central fixation. The adapters were high-contrast 0.1-deg outlines of these blank regions. All patterns had a low (0.5 c/deg) spatial frequency. The target, scotomata, and the contour adapters had the same crescent shape and were presented at 5-deg eccentricity, left and right of fixation. In a two-alternative forced-choice (2-AFC) paradigm, two adapters first flickered at 3Hz for 1.5s, followed by the target appearing randomly in one of the two locations together with the background pattern for 83.3ms. The observers were asked to indicate the target location. We used a Bayesian adaptive staircase algorithm to estimate the target contrast threshold. Target thresholds decreased with target size and increased after contour adaptation. When the background was present, regardless of its orientation, target threshold increased with background contrast. The threshold was higher with the concentric background, suggesting an orientation-specific effect. The adaptation effect was absent with the concentric background whereas it was more prominent for the radial pattern with the low contrast adapter having a stronger effect than a high contrast one. Our results demonstrate that contour adaptation can also be induced for grating patterns with evidence for an interaction between contour-adaptation and lateral-modulation effects.