A steady gray test spot looks light gray on a dark surround and dark gray on a light surround, owing to simultaneous brightness induction, perhaps based on lateral inhibition. But a test spot of the same time-averaged luminance that flickers between black and white at 15 Hz looks almost white on a dark surround and almost black on a light surround. The flickering test spot changes its brightness by five to eight times as much as the gray spot. We call this newly discovered phenomenon flicker-augmented contrast (FAC). FAC is found in all the classic demonstrations of simultaneous contrast--Heinemann's disks, McCourt's induced gratings, White's effect, Koffka's rings and Benary's cross. We shall measure FAC as a function of surround luminance, retinal eccentricity, temporal frequency, and amplitude of the test flicker. Our experiments will test between various models of FAC, based on the idea that the light and dark phases of the flickering test disk each undergo separate brightness induction from the surround before being combined by the visual system. Two models of this combination are considered: linear summation of brightness, and nonlinear """"""""winner-take-all"""""""" competitive combination. We propose that spatial increments and decrements are handled by separate Bright and Dark channels, possibly mediated by on- and off-center ganglion cells. These bright and dark signals are then combined in push-pull mode by an opponent output stage. The advantage of this opponent system is that it effectively doubles the limited intrinsic dynamic range of the neural pathways that signal luminance.
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| Anstis, S (1998) Picturing peripheral acuity. Perception 27:817-25 |
| Anstis, S (1996) Adaptation to peripheral flicker. Vision Res 36:3479-85 |
| Anstis, S (1995) Aftereffects from jogging. Exp Brain Res 103:476-8 |
