The integration of colour and motion by the human visual brain

Objects in the visual scene are defined by different cues such as colour and motion. Through the integration of these cues the visual system is able to utilize different sources of information, thus enhancing its ability to discriminate objects from their backgrounds. In the following experiments, we investigate the neural mechanisms of cue integration in the human. We show, using functional magnetic resonance imaging (fMRI), that both colour and motion defined shapes activate the lateral occipital complex (LOC) and that shapes defined by both colour and motion simultaneously activate the anterior-ventral margins of this area more strongly than shapes defined by either cue alone. This suggests that colour and motion cues are integrated in the LOC and possibly a neighbouring, more anterior, region. We support this result using an fMR adaptation technique, demonstrating that a region of the LOC adapts on repeated presentations of a shape regardless of the cue that is used to define it and even if the cue is varied. This result raises the possibility that the LOC contains cue-invariant neurons that respond to shapes regardless of the cue that is used to define them. We propose that such neurons could integrate signals from different cues, making them more responsive to objects defined by more than one cue, thus increasing the ability of the observer to recognize them.