Human Brightness Perception near Sharp Contours*

The appearances of fields that contain luminance discontinuities (e.g., the contour between a bright and a dark region) do not conform satisfactorily to predictions from models of spatial brightness interaction. Yet when the luminance distribution is systematically varied in regions separated by sharp contours, Mach-band-like gradients near the contours vary as predicted. A mechanism acting after spatial interaction may be important when fields contain contours.