Auditory motion direction encoding in auditory cortex and high-level visual cortex

Abstract

The aim of this functional magnetic resonance imaging (fMRI) study was to identify human brain areas that are sensitive to the direction of auditory motion. Such directional sensitivity was assessed in a hypothesis-free manner by analyzing fMRI response patterns across the entire brain volume using a spherical-searchlight approach. In addition, we assessed directional sensitivity in three predefined brain areas that have been associated with auditory motion perception in previous neuroimaging studies. These were the primary auditory cortex, the planum temporale and the visual motion complex (hMT/V5+). Our whole-brain analysis revealed that the direction of sound-source movement could be decoded from fMRI response patterns in the right auditory cortex and in a high-level visual area located in the right lateral occipital cortex. Our region-of-interest-based analysis showed that the decoding of the direction of auditory motion was most reliable with activation patterns of the left and right planum temporale. Auditory motion direction could not be decoded from activation patterns in hMT/V5+. These findings provide further evidence for the planum temporale playing a central role in supporting auditory motion perception. In addition, our findings suggest a cross-modal transfer of directional information to high-level visual cortex in healthy humans.

Figure 1

Experimental design and analysis. (A) Sound stimuli used in the experiment that induced the percept of left‐ or rightwards auditory motion in blocks containing 20 motion sweeps covering an arc of 30°. (B) Schematic display of the sound locations covered during auditory motion sweeps. (C) Overview of the searchlight‐based multivoxel pattern analysis employed in this study.

Figure 2

Results of searchlight‐based multivoxel pattern analysis. Group statistics projected on a cortical reconstruction of the right hemisphere of one of the subjects. T‐values indicate the extent to which performance for a location in Talairach space was higher than chance level (50%) across our nineteen subjects. Significant areas displayed on this map are a region in the right auditory cortex (mean lSVM performance = 56.9%, SEM 1.4%) and a region in the lateral occipital cortex (mean lSVM performance 56.2%, SEM 1.1%).

Figure 3

Comparison of multivariate and univariate results. (A) Overlay of areas with significant multivoxel pattern classification from Figure 1 (green, marked with asterisk) on a random‐effects map of univariate responses to auditory stimulation (average of rightwards and leftwards auditory motion). (B) Event‐related average responses to rightwards and leftwards auditory motion for the two areas identified by the spherical searchlight analysis: right auditory cortex (dark green) and right lateral occipital cortex (blue). Error bars represent the standard error of the mean across subjects.

Figure 4

Region‐of‐interest‐based analysis; (A) Regions of interest for the Heschl's gyrus, the planum temporale and hMT/V5+ as defined for the two exemplary subjects MHA18 and LSM04. (B) Group mean linear support vector machine classification performance for all regions of interest. Error bars represent the standard error of the mean across subjects.