Fig. 3.

A. The effect of target and flank contrast. Top. The effect of flank contrast at 3 target contrasts – 20% (blue), 40% (green) and 80% (red). The solid gray line is the best fitting 2-line fit to the entire data set. The fit is constrained to have a slope of zero and a value of 1 at low contrast levels. The “critical contrast” is the contrast at which threshold elevation begins to increase. Critical contrast for each target contrast is shown by the colored symbols along the abscissa. B. The critical contrasts from separate two-line fits to each data set (target contrast) vs. target contrast. The black line with unity slope shows the predicted values if the flankers acted at the level of the target feature. The dotted gray line is the slope of the best fitting line.