Task-Modulated Cortical Representations of Natural Sound Source Categories.

Jens Hjortkjær,Tanja Kassuba,Kristoffer H Madsen,Hartwig R Siebner,Martin Skov

doi:10.1093/cercor/bhx263

Abstract

In everyday sound environments, we recognize sound sources and events by attending to relevant aspects of an acoustic input. Evidence about the cortical mechanisms involved in extracting relevant category information from natural sounds is, however, limited to speech. Here, we used functional MRI to measure cortical response patterns while human listeners categorized real-world sounds created by objects of different solid materials (glass, metal, wood) manipulated by different sound-producing actions (striking, rattling, dropping). In different sessions, subjects had to identify either material or action categories in the same sound stimuli. The sound-producing action and the material of the sound source could be decoded from multivoxel activity patterns in auditory cortex, including Heschl's gyrus and planum temporale. Importantly, decoding success depended on task relevance and category discriminability. Action categories were more accurately decoded in auditory cortex when subjects identified action information. Conversely, the material of the same sound sources was decoded with higher accuracy in the inferior frontal cortex during material identification. Representational similarity analyses indicated that both early and higher-order auditory cortex selectively enhanced spectrotemporal features relevant to the target category. Together, the results indicate a cortical selection mechanism that favors task-relevant information in the processing of nonvocal sound categories.

Highlights

It is commonly accepted that the primate auditory cortex is organized in a hierarchical manner, but the neural processes involved in transforming lower-level acoustic input into “auditory objects”are still debated (Griffiths and Warren 2004; Bizley and Cohen 2013)
In Heschl’s Gyrus (HG), containing the primary auditory fields, we found that the similarity of neural response patterns correlated significantly with spectral similarity, which is expected given the tonotopic organization of primary auditory cortex (PAC) (Romani et al 1975)
Our current results suggested that the representation of temporal and spectral information in early and higher-order auditory cortex was modulated in favor of task-relevant category information

Summary

Introduction

It is commonly accepted that the primate auditory cortex is organized in a hierarchical manner, but the neural processes involved in transforming lower-level acoustic input into “auditory objects”are still debated (Griffiths and Warren 2004; Bizley and Cohen 2013). A key question is understanding how the brain integrates acoustically different sounds into invariant categories. Category-representations in more posterior parts of nonprimary auditory cortex have been attributed to sequential information such as action categories (Giordano et al 2012; Engel et al 2009; Pizzamiglio et al 2005). The brain must be able to flexibly select a category interpretation of a particular sound stimulus that is relevant in ongoing behavior. We rely critically on our ability to identify relevant auditory object information while ignoring irrelevant aspects. The cortical mechanisms responsible for the formation of goal-dependent representations of natural sound categories remain poorly understood

Methods

Results

Discussion

Conclusion