Illumination Complexity and Dot Lattice Notes

From KubovyLab

There are two variables:

1. Ratio/Luminance
2. Dot regularity

They vary as follows:

1. The Ratio/Luminance variable has two levels:
1. All dots have a constant contrast to the background
2. All dots have a constant luminance, disregarding the background
2. The Dot Regularity condition has three levels:
   1. Within a column, all dots are the same (BUT THE DOTS ALTERNATE BETWEEN COLUMNS; LIGHT IN ONE CLOLUM, AND DARK IN THE NEXT)
   2. The dots in the center rows are the same as in 2a, but are graded in equal steps around the middle row
   3. Using the same grayscale values as in 2b, and assuming that there are 9 rows, the center row is still the same as in 2a, but rows 1 and 3, 2 and 6, and 5 and 7 are swapped.
3. On top of that we have the usual manipulation of aspect ratios, with three levels of b/a, being 1.0, 1.1, and 1.2.

the spatial frequency we are aiming for was stipulated as a parameter in the last experiment that was done (0.055 c/d, amplitude = 48 cd/m2). The experiment that needs to be run has 6 conditions: "In three constant ratio conditions (Figure 7) the entire stimulus, dots and background, were modulated with a low frequency sinusoid grating (0.055 c/d, amplitude = 48 cd/m2) along |b|, keeping the dot-to-background luminance ratio constant at 0.128 (Michelson contrast) throughout the display. In three constant luminance conditions (Figure 8) the background was modulated with the same low frequency sinusoid grating. However, the mean luminance of each dot was fixed, instead of being a proportion of the background, allowing the dot-to-background luminance ratio to vary throughout the display. To ‘soften’ their edges, each dot was graded in luminance around its mean luminance."

For each of the two gradient conditions (i.e., constant ratio and constant luminance), there were three dot arrangement conditions. (a) The uniform condition (Figures 7a and 8a) alternated columns of dots that differed by a fixed (1:2) luminance ratio, but the dot luminances within a column remained uniform. (b) The graded condition (Figures 7b and 8b) kept the middle row of dot luminances identical to those in the uniform condition, the dot luminance intensity within every column was graded in 4 cd/m2 steps around the middle row mean luminance values, so that the dot intensities systematically decreased along a column in the lattice. This insured the mean luminance of each column, and the entire stimulus array, remained identical to uniform condition. (c) The rearranged condition (Figures 7c and 8c) spatially rearranged the graded dot luminances by rows. This was done in the same way as in Experiment 2’s three-swapped condition. That is, we swapped dot rows 1 and 3, 5 and 7, and 2 and 6. This preserved the mean luminance of each column and the entire stimulus array, making it identical to the other two conditions. Moreover, while this condition changed the spatial ordering of dots luminances within a column, from a gradual continuum of dots to columns with an unsystematic array of dots, it retained the spatial ordering of dots luminances within each row.