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James A. Schirillo, John T. Cooley, Thomas J. Barra; Dot lattice regularity influences grouping by similarity. Journal of Vision 2004;4(8):351. doi: 10.1167/4.8.351.
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© ARVO (1962-2015); The Authors (2016-present)
We predict that dots varying in luminance group according to an overall dot lattice luminance pattern. To create the appearance of changing illumination, we convolved the dot lattices with a low spatial frequency luminance grating. In half of the conditions the sinusoid to dot luminance ratio was constant, while in the other conditions it was independent of the background (i.e., constant luminance). In two conditions (i.e., constant ratio (A) & constant luminance (B)) alternating columns of dots differed by a fixed luminance ratio while the luminances within a column were uniform. Two other conditions graded the dot luminance intensity within a column (i.e., constant ratio (C) & constant luminance (D)). Two final conditions spatially rearranged the graded dot luminances within a column (i.e., constant ratio (E) & constant luminance (F)). Each trial has a different column to row spatial aspect ratio. A 4AFC was used to indicate the perceived dot lattice orientation. In the constant ratio conditions, observers decreased their likelihood of perceiving the stimuli as grouped by column systematically from graded (C) to uniform (A) to rearranged (E) conditions. The constant luminance conditions produced similar findings (i.e., conditions A ∼ B and E ∼ F), except the graded condition (B) was much more erratic that its comparable constant ratio condition (C). This suggests that graded dot luminances strongly bias grouping within columns, but only when constant ratios allow for discounting the illuminant. Grouping is reversed by spatially rearranging these same dots.
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