Sensory and striatal areas integrate auditory and visual signals into behavioral benefits during motion discrimination.

For effective interactions with our dynamic environment, it is critical for the brain to integrate motion information from the visual and auditory senses. Combining fMRI and psychophysics, this study investigated how the human brain integrates auditory and visual motion into benefits in motion discrimination. Subjects discriminated the motion direction of audiovisual stimuli that contained directional motion signal in the auditory, visual, audiovisual, or no modality at two levels of signal reliability. Therefore, this 2 × 2 × 2 factorial design manipulated: (1) auditory motion information (signal vs noise), (2) visual motion information (signal vs noise), and (3) reliability of motion signal (intact vs degraded). Behaviorally, subjects benefited significantly from audiovisual integration primarily for degraded auditory and visual motion signals while obtaining near ceiling performance for "unisensory" signals when these were reliable and intact. At the neural level, we show audiovisual motion integration bilaterally in the visual motion areas hMT+/V5+ and implicate the posterior superior temporal gyrus/planum temporale in auditory motion processing. Moreover, we show that the putamen integrates audiovisual signals into more accurate motion discrimination responses. Our results suggest audiovisual integration processes at both the sensory and response selection levels. In all of these regions, the operational profile of audiovisual integration followed the principle of inverse effectiveness, in which audiovisual response suppression for intact stimuli turns into response enhancements for degraded stimuli. This response profile parallels behavioral indices of audiovisual integration, in which subjects benefit significantly from audiovisual integration only for the degraded conditions.