A Glass pattern is made up of randomly dispersed dot pairs, or dipoles, whose orientation is regulated by a geometric transform that determines an observer’s global percept. A local mechanism that associates dot pairs into dipoles and a global process that aggregates the dipoles into a global structure is involved in the perception of Glass patterns. For a study, researchers employed a variation of Glass patterns made up of randomly dispersed tripoles rather than dipoles to evaluate the effect of color contrast on perceptual grouping. Each tripole was made up of one anchor dot and two context dots. When the anchor dot was grouped with one of the context dots, the global percept was of a clockwise spiral, but when the anchor dot was grouped with the other dot, the global percept was of a counter-clockwise spiral.

Each pattern’s dots varied in the same color direction but with differing contrasts. Four hues were used: red, green, blue, and yellow. Observers had to judge whether the spiral in each trial rotated clockwise or counterclockwise. The likelihood of a context dot being associated with the anchoring dot grew until a particular degree of color contrast was reached, then reduced as the contrast increased further. As the contrast of the other context dot grew, so did this likelihood. Existing models in the literature did not explain the results, but a divided inhibition model did. The equiluminant contrast result was comparable to the previously published inverted U-shaped function for luminance contrast result, except that the color contrast model had a smaller self-inhibition component.