Simultaneous EEG-fMRI brain signatures of auditory cue utilization.

Mathias Scharinger,Jonas Obleser,Till Nierhaus,Bjã¶Rn Herrmann

doi:10.3389/fnins.2014.00137

Abstract

Optimal utilization of acoustic cues during auditory categorization is a vital skill, particularly when informative cues become occluded or degraded. Consequently, the acoustic environment requires flexible choosing and switching amongst available cues. The present study targets the brain functions underlying such changes in cue utilization. Participants performed a categorization task with immediate feedback on acoustic stimuli from two categories that varied in duration and spectral properties, while we simultaneously recorded Blood Oxygenation Level Dependent (BOLD) responses in fMRI and electroencephalograms (EEGs). In the first half of the experiment, categories could be best discriminated by spectral properties. Halfway through the experiment, spectral degradation rendered the stimulus duration the more informative cue. Behaviorally, degradation decreased the likelihood of utilizing spectral cues. Spectrally degrading the acoustic signal led to increased alpha power compared to nondegraded stimuli. The EEG-informed fMRI analyses revealed that alpha power correlated with BOLD changes in inferior parietal cortex and right posterior superior temporal gyrus (including planum temporale). In both areas, spectral degradation led to a weaker coupling of BOLD response to behavioral utilization of the spectral cue. These data provide converging evidence from behavioral modeling, electrophysiology, and hemodynamics that (a) increased alpha power mediates the inhibition of uninformative (here spectral) stimulus features, and that (b) the parietal attention network supports optimal cue utilization in auditory categorization. The results highlight the complex cortical processing of auditory categorization under realistic listening challenges.

Highlights

The interpretation of acoustic signals is an essential human skill for goal-directed behavior and vocal communication
Even though the behavioral measure of cue utilization only marginally differed between conditions, less reliance on spectral cues under sound degradation corresponded to increased activation in left planum temporale (PT) and right inferior parietal lobule (IPL)
With respect to our data, we propose that alpha power increases gated the neural processing of acoustic information that differed in task-relevance between conditions: The introduction of spectral degradation in the second half of our experiment changed the relative informativeness or task-relevance of the spectral and duration cues, with spectral peak becoming less informative than stimulus duration

Summary

Introduction

The interpretation of acoustic signals is an essential human skill for goal-directed behavior and vocal communication. The core process underlying this skill—auditory categorization—has been shown to be highly flexible and adaptive, and allows, for instance, speaker recognition in a cocktail party situation (Zion Golumbic et al, 2013), or speech comprehension in noise (Nahum et al, 2008). In both cases, attention has to be directed to the most informative aspect of the acoustic signal (Hill and Miller, 2010). It has been further proposed that brain regions showing high alpha power undergo inhibition, which in turn allows enhanced processing of task-relevant information (Klimesch et al, 2007)

Methods

Discussion

Conclusion