Processing of speech and non-speech sounds in the supratemporal plane:
auditory input preference does not predict sensitivity to statistical structure
Abstract:
The supratemporal plane contains several functionally heterogeneous subregions
that respond strongly to speech. Much of the prior work on the issue of speech
processing in the supratemporal plane has focused on neural responses to single
speech vs. non-speech sounds rather than focusing on higher-level computations
that are required to process more complex auditory sequences. Here we examined
how information is integrated over time for speech and non-speech sounds by
quantifying the BOLD fMRI response to stochastic (non-deterministic) sequences
of speech and non-speech naturalistic sounds that varied in their statistical
structure (from random to highly structured sequences) during passive listening.
Behaviorally, participants were accurate in segmenting speech and non-speech
sequences, though they were more accurate for speech. Several supratemporal
regions showed increased activation magnitude for speech sequences (preference),
but, importantly, this did not predict sensitivity to statistical structure: (i)
several areas showing a speech preference were sensitive to statistical
structure in both speech and non-speech sequences, and (ii) several regions that
responded to both speech and non-speech sounds showed distinct responses to
statistical structure in speech and non-speech sequences. While the behavioral
findings highlight the tight relation between statistical structure and
segmentation processes, the neuroimaging results suggest that the supratemporal
plane mediates complex statistical processing for both speech and non-speech
sequences and emphasize the importance of studying the neurocomputations
associated with auditory sequence processing. These findings identify new
partitions of functionally distinct areas in the supratemporal plane that cannot
be evoked by single stimuli. The findings demonstrate the importance of going
beyond input preference to examine the neural computations implemented in the
superior temporal plane.