Modulation of early auditory processing by visually based sound prediction.

Brain activity was measured by magnetoencephalography (MEG) to investigate whether the early auditory system can detect changes in audio-visual patterns when the visual part is presented earlier. We hypothesized that a template underlying the mismatch field (MMF) phenomenon, which is usually formed by past sound regularities, is also used in visually based sound prediction. Activity similar to the MMF may be elicited by comparing an incoming sound with the template. The stimulus was modeled after a keyboard: an animation in which one of two keys was depressed was accompanied by either a lower or higher tone. Congruent audio-visual pairs were designed to be frequent and incongruent pairs to be infrequent. Subjects were instructed to predict an incoming sound based on key movement in two sets of trials (prediction condition), whereas they were instructed not to do so in the other two sets (non-prediction condition). For each condition, the movement took 50 ms in one set (Delta = 50 ms) and 300 ms in the other (Delta = 300 ms) to reach the bottom, at which time a tone was delivered. As a result, only under the prediction condition with Delta = 300 ms was additional activity for incongruent pairs observed bilaterally in the supratemporal area within 100-200 ms of the auditory stimulus onset; this activity had spatio-temporal properties similar to those of MMF. We concluded that a template is created by the visually based sound prediction only after the visual discriminative and sound prediction processes have already been performed.