A primate model of human cortical analysis of auditory objects

Abstract

The anatomical organization of the auditory cortex in old world monkeys is similar to that in humans. But how good are monkeys as a model of human cortical analysis of auditory objects? To address this question I explore two aspects of auditory objectprocessing: segregation and timbre. Auditory segregation concerns the ability of animals to extract an auditory object of relevance from a background of competing sounds. Timbre is an aspect of object identity distinct from pitch. In this work, I study these phenomena in rhesus macaques using behaviour and functional magnetic resonance imaging (fMRI). I specifically manipulate one dimension of timbre, spectral flux: the rate of change of spectral energy.I present this thesis in five chapters. Chapter 1 presents background on auditory processing, macaque auditory cortex, models of auditory segregation, and dimensions of timbre. Chapter 2 presents an introduction to fMRI, the design of the fMRI experiments and analysis of fMRI data, and macaque behavioural training techniques employed. Chapter 3 presents results from the fMRI and behavioural experiments on macaques using a stochastic figure-ground stimulus. Chapter 4 presents the results from the fMRI experiment in macaques using spectral flux stimulus. Chapter 5 concludes with a general discussion of the results from both the studies and some future directions for research.In summary, I show that there is a functional homology between macaques and humans in the cortical processing of auditory figure-ground segregation. However, there is no clear functional homology in the processing of spectral flux between these species. So I conclude that, despite clear similarities in the organization of the auditory cortex and processing of auditory object segregation, there are important differences in how complex cues associated with auditory object identity are processed in the macaque and human auditory brains.