Predictability modulates motor-auditory interactions in self-triggered audio-visual apparent motion.

We studied an effect of predictability in an audio-visual apparent motion task using magnetoencephalography. The synchronous sequences of audio-visual stimuli were self-triggered by subjects. The task was to detect the direction of the apparent motion in experimental blocks in which the motion either started from the side selected by subjects (predictable condition) or was random (unpredictable condition). Magnetic fields yielded three patterns of activity in the motor, auditory, and visual areas. Comparison of the dipole strength between predictable and unpredictable conditions revealed a significant difference of the preparatory motor activity in the time interval from -450 to -100 ms before self-triggering the stimulus. Perception of the audio-visual apparent motion was also modulated by predictability. However, the modulation was found only for the auditory activity but not for the visual one. The effect of predictability was selective and modulated only the auditory component N1 (100 ms after stimulus), which reflects initial evaluation of stimulus meaning. Importantly, the preparatory motor activity correlates with the following auditory activity mainly in the same hemisphere. Similar modulation by predictability of the motor and auditory activities suggests interactions between these two systems within an action-perception cycle. The mechanism of these interactions can be understood as an effect of anticipation of the own action outcomes on the preparatory motor and perceptual activity.