Grating induction: a new explanation for stationary phantom gratings.

The magnitude of brightness variations within test fields of grating induction and phantom grating type displays was measured using a pointwise brightness matching paradigm. A range of test field luminances was sampled which encompassed those reported to give rise to both in-phase phantom and counterphase induced gratings. Results from four observers failed to reveal the existence of stationary "in phase" phantom gratings: at all test field luminances the spatial phase of brightness modulations was consistently opposite to that of the inducing grating. At low or high test field luminances, however, test field luminance matches to the bright or dark half-cycles of induced gratings approximate the luminances of the troughs or peaks of the dark or bright half-cycles of the inducing gratings, respectively. Thus, at low test field luminances the dark half-cycle of the inducing grating may appear to continue across the dark test field, and similarly, at high test field luminances the bright half-cycle may appear continuous with the bright test field. Previously misidentified as being "in-phase" with the inducing grating, the appearance of "phantoms" is suggested to arise due to the apparent brightness continuity of these induction-produced half-cycles of the induced grating across the test field.