Brain activation during audiovisual exposure anticipates future perception of ambiguous speech

Abstract

In modern perceptual neuroscience, the focus of interest has shifted from a restriction to individual modalities to an acknowledgement of the importance of multisensory processing. One particularly well-known example of cross-modal interaction is the McGurk illusion. It has been shown that this illusion can be modified, such that it creates an auditory perceptual bias that lasts beyond the duration of audiovisual stimulation, a process referred to as cross-modal recalibration (Bertelson et al., 2003). Recently, we have suggested that this perceptual bias is stored in auditory cortex, by demonstrating the feasibility of retrieving the subjective perceptual interpretation of recalibrated ambiguous phonemes from functional magnetic resonance imaging (fMRI) measurements in these regions (Kilian-Hütten et al., 2011). However, this does not explain which brain areas integrate the information from the two senses and represent the origin of the auditory perceptual bias. Here we analyzed fMRI data from audiovisual recalibration blocks, utilizing behavioral data from perceptual classifications of ambiguous auditory phonemes that followed these blocks later in time. Adhering to this logic, we could identify a network of brain areas (bilateral inferior parietal lobe [IPL], inferior frontal sulcus [IFS], and posterior middle temporal gyrus [MTG]), whose activation during audiovisual exposure anticipated auditory perceptual tendencies later in time. We propose a model in which a higher-order network, including IPL and IFS, accommodates audiovisual integrative learning processes, which are responsible for the installation of a perceptual bias in auditory regions. This bias then determines constructive perceptual processing.