Higher Order Visual Location Learning Does Not Explain Multisensory Enhancement of Sound Localization (Reply to Vroomen and Stekelenburg 2021).

In a recent study, we reported that multisensory enhancement (ME) of auditory localization after exposure to spatially congruent audiovisual stimuli and crossmodal recalibration in the ventriloquism aftereffect (VAE) are differently affected by the temporal stimulation frequency with which the audiovisual exposure stimuli are presented. Because audiovisual stimulation at 10 Hz rather than at 2 Hz selectively abolished the VAE but did not affect the ME, we concluded that distinct underlying neural mechanisms are involved in the two effects. A commentary on our paper challenged this interpretation and argued that the ME might have been spared simply because participants had acquired higher order knowledge about the loudspeaker locations from the visual stimulus locations in the ME condition, or because the ME was generally more reliable than the VAE. To test this alternative explanation of our results, we conducted an additional control experiment in which participants localized sounds before and after exposure to unimodal visual stimulation at the loudspeaker locations. No significant reduction of auditory localization errors was found after unimodal visual exposure, suggesting that higher order visual location learning cannot sufficiently explain the significant ME that was observed after audiovisual exposure in our previous study. These new results confirm previous findings pointing toward dissociable neural mechanisms underlying ME and VAE.