Some effects of contour on simultaneous brightness contrast.

Abstract

Simultaneous brightness contrast was measured as a function of: (a) the orientation of a test object, shaped as a figure 8, on a half light, half black surround, (b) type and width of a contour separating the figure halves on the divided background. Forty-eight adult Ss matched the brightness of the figure half on the dark background with that on the light surround. Subjective contrast was significantly greater: (a) when the figure 8 was presented with its rings on backgrounds of different brightness than when each ring lay on both backgrounds, (b) when figure halves were moved apart, each into its own surround, rather than when a dividing line separated the halves, (c) as width of the contour between halves was increased. The results are discussed in terms of the contribution of the border to subjective contrast obtained with complex stimulus configurations.