Hierarchical Processing of Auditory Objects in Humans

Sukhbinder Kumar,Karl J Friston,Timothy D Griffiths,Klaas E Stephan,Jason D Warren,Philip E Bourne

doi:10.1371/journal.pcbi.0030100

Abstract

This work examines the computational architecture used by the brain during the analysis of the spectral envelope of sounds, an important acoustic feature for defining auditory objects. Dynamic causal modelling and Bayesian model selection were used to evaluate a family of 16 network models explaining functional magnetic resonance imaging responses in the right temporal lobe during spectral envelope analysis. The models encode different hypotheses about the effective connectivity between Heschl's Gyrus (HG), containing the primary auditory cortex, planum temporale (PT), and superior temporal sulcus (STS), and the modulation of that coupling during spectral envelope analysis. In particular, we aimed to determine whether information processing during spectral envelope analysis takes place in a serial or parallel fashion. The analysis provides strong support for a serial architecture with connections from HG to PT and from PT to STS and an increase of the HG to PT connection during spectral envelope analysis. The work supports a computational model of auditory object processing, based on the abstraction of spectro-temporal “templates” in the PT before further analysis of the abstracted form in anterior temporal lobe areas.

Highlights

The concept of an auditory object is controversial [1]
The past decade has seen a phenomenal rise in applications of functional magnetic resonance imaging for both research and clinical applications
We have examined the interactions between three regions—Heshl’s gyrus (HG), planum temporale (PT), and superior temporal sulcus (STS)— that have been implicated in processing the spectral envelope of sounds

Summary

Introduction

The concept of an auditory object is controversial [1]. The term can be applied to a sound source like a voice, or an acoustic event generated by a source such as a vowel sound. There are features of the object that are independent of the detailed structure of the sound: we can recognise the same vowel, or voice, regardless of the pitch In these examples, the spectral envelope of the sound determines the particular vowel sound produced, and is, in general, one of the important acoustic features that determine its perceived timbre (Figure 1; spectrogram of the same vowel at different pitch). The spectral envelope of the sound determines the particular vowel sound produced, and is, in general, one of the important acoustic features that determine its perceived timbre (Figure 1; spectrogram of the same vowel at different pitch) In this experiment we consider the ‘‘abstraction’’ of the spectral envelope a critical aspect of auditory cognition that defines auditory objects before semantic processing. Such analysis allows generalisation between different exemplars (e.g., the same vowel at a different pitch) in an analogous manner to the generalisation between visual objects that are seen from different perspectives

Objectives

Results

Conclusion