Grouping based on phenomenal proximity.

The question was raised whether the Gestalt law of grouping by proximity is based on proximity of stimuli on the retina or perceived proximity in phenomenal space. To tease apart these 2 possibilities an earlier experiment of Corbin was repeated in which the stimulus array is tilted back into the 3rd dimension. By including a measure of constancy for the perceived distance between points it was possible to show in 2 experiments, that the crucial factor is phenomenal proximity. This finding questions the Gestalt assumption that grouping is based on certain objectively given features within the stimulus. The grouping of stimuli on the basis of proximity is one of the major Gestalt laws of the spontaneous organization of the visual field. Presumably, more proximal stimuli on the retina yield stronger forces of attraction between their corresponding loci of excitation in the brain than less proximal stimuli. However, it has not been demonstrated that it is the anatomical closeness within the proximal stimulus array which governs grouping. The only investigator who ever raised this question was Corbin (1942), who speculated that grouping may be accomplished on the basis of the perceived spatial relations between the points in a stimulus array, and that this phenomenally perceived proximity and retinal proximity, although usually coinciding, can be experimentally separated and thrown into conflict. Corbin's method was to present an array of illuminated points in the dark seen as columns when in the frontal plane. A gradual lateral tilting of the stimulus configuration into the third dimension progressively foreshortened the horizontal distance between the columns as projected to the retina. Corbin reasoned that under monocular