Interocular Grouping of Visual Attributes during Binocular Rivalry

The need to revise the eye competition hypothesis of binocular rivalry, and to include the role of stimulus competition has been demonstrated recently by Kovács, Papathomas, Feher, and Yang (1996 Proceedings of the National Academy of Sciences of the USA 93 15508 – 15511) and Logothetis, Leopold, and Sheinberg [1996 Nature (London) 380 621 – 624]. Kovács et al showed that observers can obtain one-colour percepts when presented with chromatically rivalrous stimuli, even when there are targets of two different colours in each eye. In this study we investigate whether other attributes, in addition to colour, can drive interocular grouping, and how they interact.

We extended the ‘patchwork’ rivalrous stimuli (Kovács et al) to study how colour, orientation, spatial frequency, and motion can group interocularly, and how they interact in grouping. Gabor patches are used, because they allow conjunctions of attributes to be formed systematically. To study the ability of an attribute (or a combination of attributes) to group interocularly, we induce rivalry by virtue of interocular differences in that attribute (or combination), and keep the other attributes fixed in both eyes' images. The main advantage of these stimuli is that they enable us to decorrelate the effects of eye competition and percept competition in binocular rivalry. The data show that colour is the most powerful attribute in grouping, and that combinations are stronger than single attributes. Overall, the results indicate that similarity in low-level attributes can drive interocular grouping, and that binocular rivalry follows complex rules of perceptual organisation that cannot be accounted for by eye suppression alone.