Auditory and visual attention modulate motion processing in area MT+.

Behavioral and physiological studies have established that visual attention to a given feature or location can modulate early visual processing. In the present experiment, we asked whether auditory attention can likewise influence visual processing. We used a visual illusion, the motion aftereffect (MAE), to assess the effects of visual and auditory attention on motion processing in human area MT+. We acquired psychophysical and functional magnetic resonance imaging (fMRI) data while subjects fixated and viewed moving and stationary stimuli in alternating blocks. For each of four motion conditions, we measured the duration of the subsequent MAE, the time for activity in MT+ to return to baseline after motion adaptation (decay time), and the magnitude of MT+ activity during motion adaptation. For each subject, we first obtained measures of motion processing in the absence of attentional demands, by comparing reversing and expanding motion conditions. Subjects perceived the MAE following adaptation to expanding but not reversing motion, as observed previously, and decay times in MT+ were selectively prolonged after expanding motion. We then assessed the effects of performing either a visual or an auditory attentional task during expanding motion adaptation. Performance of the attentional task, whether visual or auditory, produced a significant reduction of subsequent MAE perception and associated decay times in MT+, as compared to expanding motion with fixation only. Both attentional tasks also reduced the magnitude of activation during motion adaptation. These data show that auditory attention, like visual attention, can modify sensory processing at a remarkably early stage of the visual hierarchy.