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Mark E. McCourt, Barbara Blakeslee; Spatiotemporal dependencies of brightness induction. Journal of Vision 2006;6(6):705. doi: 10.1167/6.6.705.
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The brightness of a target region is modulated by the luminance of surrounding regions. Brightness induction is believed to be low-pass with respect to both spatial and temporal frequency, and to extend only to relatively low frequencies. However the methods used to measure induction magnitude to date have made accurate determinations of its temporal frequency response difficult. We exploit a novel technique in which we sinusoidally counterphase the inducing grating of a grating induction display to create a counterphasing induced grating within the test field. Adding a second (genuine luminance) counterphasing grating in spatial and temporal quadrature phase to the modulating induced grating leverages the induced brightness modulation into a traveling wave (motion), to which we are exquisitely sensitive. The quadrature sum moves leftward or rightward depending upon whether the temporal phase of the second luminance grating is plus or minus 90 degrees relative to the induced grating. Adding a third (genuine luminance) canceling grating into the test field permits a precise estimation of induction magnitude at manifold spatial and temporal frequencies, since when the canceling grating exactly nulls the induced grating motion energy within the test field is left/right balanced, resulting in 50:50% left/right judgments in a forced-choice motion direction task. Using this technique we have measured the spatiotemporal dependencies of brightness induction across a wide range of spatial and temporal frequencies. Brightness induction extends to much higher frequencies than have heretofore been thought possible.
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