The effect of stimulus range on perceived contrast: evidence for contrast gain control.

In audition, loudness matches across frequency are affected by the range of stimuli employed at each frequency (e.g., Marks, 1988; Schneider & Parker, 1990). For example, the loudness of a 500-Hz tone that matches the loudness of a 60-dB 2-kHz tone can be changed by as much as 10 to 20 dB by manipulating the range of intensity values to which the listener is exposed. The goal of the present study was to determine whether stimulus range had a similar effect on the perceived contrast of vertical gratings whose spatial frequencies were either 1 or 4 cycles/deg. Viewers judged the perceived contrasts of 1 and 4 cycle/deg gratings intermixed within a session using the method of magnitude estimation. Four different conditions were created by combining either a set of low-contrast or high contrast gratings at one frequency with a broad range of contrasts at the other frequency. When the broad-range set was at 1 cycle/deg, contrast matches across spatial frequencies were unaffected by changing the range of the 4-cycle/deg gratings from low to high. However, when the broad-range set was at 4 cycles/deg, contrast matches were changed by changing the range of the 1 cycle/deg gratings. This asymmetry in the "range effect" was shown to be consistent with the characteristics of the two channels' receptive-field profiles.