Independent binocular integration for form and colour.

Although different features of an object are processed in anatomically distinct regions of the cerebral cortex, they often appear bound together in perception. Here, using binocular rivalry, we reveal that the awareness of form can occur independently from the awareness of colour. First, we report that, if both eyes briefly view a grating stimulus prior to the presentation of the same grating in one eye and an orthogonal grating in the other, subjects tend to report perceptual dominance of the non-primed grating. The primer was most effective when it was similar in orientation, spatial frequency and spatial phase to one of the rival images. Next, we showed that the process underlying the binocular integration of chromatic information was selectively influenced by the colour of a previously presented stimulus. We then combined these paradigms by using a primer that had the same colour as one rival stimulus, but the same form as the other stimulus. In this situation, we found that rival stimuli differing in form and colour can sometimes achieve states of dominance in which the chromatic information from one eye's image combines with the form of the other eye's image temporarily creating a binocular impression that corresponds with neither monocular component. Finally, we demonstrated that during continuous viewing of rival stimuli differing in form and colour, chromatic integration could occur independently of form rivalry. Paradoxically, however, we found that changes to the form of the stimulus had more of an influence on chromatic integration than on form rivalry. Together these phenomena show that the neural processes involved in integrating information from the two eyes can operate selectively on different stimulus features.