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FH Durgin; Lateral Interactions of Texture Density (Kurtosis) . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2912.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: A texture appears less dense when surrounded by another texture (simultaneous contrast of texture density). Some previous studies (e.g., MacKay, 1973) have confounded texture density with spatial frequency, but the textures used here were composed of luminance-balanced dots to hold spatial frequency content constant. Three aspects of the surround texture were studied in order to help dissociate texture density from texture contrast and spatial frequency. These variables were interocular effectiveness, spatial proximity, and the density of the surround relative to the target texture. Methods: All studies were conducted using the same mirror haploscope apparatus, though viewing was normally binocular. Targets and match textures were circles of texture (5 deg diameter) centered 5.5 deg to the left and right of fixation. One side was surrounded by an 12 x 12 deg square of texture. Surround side was varied. Target densities varied from 6 to 20 dot per sq. deg. A staircase method was used to assess the PSE for density under various surround conditions. In the Interocular study (N=15), surround densities were always double that of the target texture. Displays were presented binocularly, monocularly, or interocularly (targets in one eye, surround in the other). In the Relative Density study (N=14), the surround density was 0.5, .71, .84, 1.0, 1.19, 1.41, or 2.0 times the target density. Analyses were conducted in log space, but are reported as ratios of matched density to surrounded-target density at PSE. In the Proximity study (N=15), an annular gap between surround and target varied from 0 to 3.5 degrees by .5 degree increments. (For this study, targets were 4 deg diameter, presented within a 16 x 16 deg surround.) Results: PSEs in the Binocular (.84), Monocular (.84) and Interocular conditions (.86) did not differ from one another, F(2,14) = 0.6, n.s. PSEs in the Proximity study dropped off from 0 deg separation (.87), but were still reliably less than 1.0 at 1 deg (.92), 2 deg (.95), and 3 deg (.95) separation. The Relative Density study showed that perceived target density was decreased even by lower-density surrounds, though the decrease increased with surround density. The PSEs (from .5 to 2.0 surrounds) were: .99, .98, .94, .94, .91, .86, and .83. All but the first two are reliably less than 1. Conclusion: Lateral interactions of texture density are binocular unlike those of luminance contrast and may span several degrees. Because low-density surrounds still reduce the perceived density of a surrounded target, however, density is evidently a zero-based scalar dimension unlike spatial frequency.
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