Neural auditory intensity discrimination during naturalistic listening: a brain decoding study
Neural discrimination of auditory intensity is one of the fundamental questions in human auditory perception. Human neuroimaging studies have demonstrated specific neural activations during intensity discrimination tasks. The detailed functional anatomy, however, remains elusive. Most of the existing studies examined the entire auditory cortex as a whole, neglecting the potential functional differentiation within the auditory cortex. Moreover, these previous results based on controlled auditory stimuli might not necessarily extend to the neural mechanism of natural auditory processing. In this study, we propose a novel brain decoding method to examine neural encoding of intensity discrimination during naturalistic auditory experience. Here, we used publically available dataset (http://studyforrest.org) in which high resolution functional magnetic resonance imaging (fMRI) was acquired when the participants freely listened to the audio-version of the movie “Forrest Gump”. We found the sensitivity and accuracy of intensity discrimination in the auditory cortex critically depend on the divergences in intensity levels, yielding a sigmoidal relationship. Furthermore, anatomical subdivisions of auditory cortex revealed great functional diversity and lateralization in intensity discrimination. While bilateral activations were observed in primary auditory cortex, enhanced left-lateralization effects were shown in inferior frontal gyrus, anterior middle temporal gyrus and temporal-occipital junction. Our findings underscore the value of naturalistic paradigms in mapping auditory processing in the brain: naturalistic paradigm contains enriched and complex natural sounds, which not only improve the ecological validity but also alleviate the discrepancies caused by the differences in stimulus types and task designs in previous studies. The multidisciplinary methodology we developed here provides an analytical framework for studying neural encoding of complex auditory stimuli.