Direct physiological evidence for scene segmentation by temporal coding.

Theoretical studies have suggested that scene segmentation may be accomplished by a temporal coding mechanism using synchronization of neuronal responses. Here we report a direct experimental test of this hypothesis. Neuronal responses were recorded simultaneously from two to four sites with overlapping receptive fields in cat visual cortex. Correlation analysis revealed that all cells synchronized their responses irrespective of their orientation preference when they were activated by a single light bar. However, when stimulated with two superimposed light bars of different orientations, the same cells segregated into distinct assemblies according to their orientation preferences. Within each of these assemblies responses were synchronized, but correlation was absent between the two assemblies. These results are compatible with the hypothesis that responses to individual objects in a scene are distinguished by synchrony, whereas responses to different objects show no temporal correlation, thus allowing for the segmentation of superimposed stimuli. We conclude that stimulus-specific synchronization of spatially distributed neuronal responses may provide a physiological mechanism for scene segmentation.