Purpose. Both grating induction (GI) and simultaneous brightness contrast (SBC) are long-range suprathreshold spatial interaction effects. SBC produces a homogeneous brightness change within an enclosed test field, and is often attributed to a fill-in mechanism in which the average perimeter contrast of the bounded region determines the brightness percept. GI induces a spatial brightness variation (a grating) in an extended test field. Fill-in cannot account for GI because it predicts a homogeneous test field and no brightness induction. The present experiment asks whether the mechanism underlying GI can account for SBC or if different brightness mechanisms are required to explain these effects. Methods. Point-by point matching was employed to assess brightness at 30 to 70 locations across GI (1° x 32° continuous test field), SBC (two 1° x 1° square test fields) and three transitional displays with horizontally extended but separate test fields (1° x 8°, 12°, or 14°). This allowed both induction magnitude and spatial structure in the test fields to be quantified. Subjects adjusted the luminance of a 1° x 0.25° matching stimulus located in a spatially homogeneous region of the display. A thin bright line pointed to the region of the test field that was to be matched in brightness. Test field luminance was set to the display mean (50 cd/m2). The inducing pattern in all conditions was one cycle of a vertical sine wave grating (0.031 cyc/deg, 0.75 contrast) in cosine phase. Results. Mean matching luminance for three subjects was compared across SBC, GI and transitional stimuli. Spatial structure in induced test field brightness was evident in both the GI and transitional stimuli. Discontinuities in both induction strength and structure would be expected if a fill-in process operated in SBC and transition test fields, but not in continuous GI test fields. No discontinuities were found. Conclusions. The results are consistent with the hypothesis that a single mechanism underlies SBC and GI, but it is not the fill-in mechanism classically invoked to explain SBC.
|Original language||English (US)|
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - Feb 15 1996|
ASJC Scopus subject areas
- Sensory Systems
- Cellular and Molecular Neuroscience