The spatial and temporal properties of the contour erasure effect and perceptual filling-in

Contour erasure describes the phenomenon that after brief flicker adaptation at the edge of an object, the object disappears and is replaced by the background - highlighting the importance of edges in perceiving a surface. The underlying mechanism remains unknown. The current study investigates the characteristics and functional properties of contour erasure, and its relationship with related phenomena such as perceptual filling-in, forward masking, and contrast adaptation. We used a homogeneous disk as a target, and circles that corresponded to the outline of the target disk as the adapter. Using a two-alternative forced choice (2AFC) paradigm, each trial began with a counterphase flickering adapter, followed by the target randomly presented in one of the two locations. Participants indicated the target location with a button press. The target detection threshold elevation relative to the no adaptation condition was used as an index of the adaptation effect. We manipulated two spatial properties (eccentricity and the adapter size) plus three temporal properties (adapter flickering rate, adaptation duration, and interstimulus interval [ISI]). Results indicated that the adaptation effect increased with eccentricity, flickering rate (plateauing at 6 hertz [Hz]) and adaptation duration, but decreased with longer ISI and for adapter sizes that were larger than the target. The target threshold first increased then decreased as the adapter size decreased from that of the target, indicating a size tuning that is slightly smaller than the target. Our results indicate that contour erasure shares some of the key features of other well-known perceptual phenomena like filling in and contrast adaptation.