Flicker Sensitivity and Apparent Brightness as a Function of Surround Luminance*

Both brightness matching and sensitivity to sinusoidal flicker were measured for different contrasts using a 30′ test field surrounded by a 6° annulus. Test fields that produced 10 000-, 3000-, 1000-, 300-, 100-, and 30-td retinal illuminance were used. Matched brightness of the test field remained constant as surround luminance was increased from zero, then fell rapidly when the luminance of the surround was one tenth that of the test field. Flicker sensitivity followed a different function: It began to increase when the surround had one hundredth the luminance of the test field, reached a peak at one third, and then fell rapidly. The sensitivity enhancement was independent of flicker frequency. The results are attributed to spatial interactions in the visual system.