The temporal course of reduction of test-stimulus effectiveness under conditions of metacontrast was studied with two different suprathreshold brightness-matching procedures. (1) Test-stimulus luminance was varied to make apparent brightness of the test stimulus equal to the brightness of a constant-luminance reference stimulus. (2) Reference-stimulus luminance was varied to match the apparent brightness of a test stimulus maintained at constant luminance. Functions obtained from two observers when the teststimulus luminance was varied were typical metacontrast functions with maximum reduction of teststimulus effectiveness when the test stimulus preceded the background by 50 ms, and the shape of the functions was highly similar to functions obtained previously with a disk-ring stimulus configuration. Functions obtained by varying reference-stimulus luminance were highly variable both between observers and within observers. The difficulties encountered with this second method probably resulted from glare from high-luminance test and surround fields.

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