Orientation selectivity of the McCollough. effect: Analysis by equivalent contrast transformation

Using a color-cancellation technique, the strength of the McCollough effect was measured in units of excitation purity. The strength was studied both as a function of the contrast of the adapting gratings and as a function of the angle × between the axes of the test and the adapting gratings. Results were well described as a linear function of the contrast of the adapting gratings and as a cos(2×) function of the angle. Both functions were combined to express an equivalent contrast transformation which converts the measurements of orientation tuning into a unit comparable to that used for other kinds of orientation-specific aftereffects. The orientation tuning was found to be very broad with a half-width at half amplitude of approximately 27°. This estimate is considered to be a substantial underestimate of the actual tuning of the aftereffect’s substrate.