Figure-ground processing in the auditory cortex of the macaque monkey

Abstract

Natural sensory scenes are often very complex, with a multitude of overlapping objects in space and time. In order to direct behaviour, a critical aspect of everyday perception is the segregation and grouping of relevant features from those scenes, known as figure-ground segregation. The neurobiological basis of auditory figureground processing is poorly understood. To gain insights into different aspects of this process, I have investigated the behavioural, systemic and neuronal mechanisms the brain uses to segregate and group temporally coherent elements from a complex acoustic scene in macaque monkeys. This thesis presents the result of this research in five chapters: Chapter 1 reviews the fundamental basics of auditory scene analysis and the auditory system. Chapter 2, 3 and 4 present experimental work and cover figure detection behaviour (Chapter 2), systemic organisation of figure-ground analysis (Chapter 3) and the underlying neuronal mechanisms (Chapter 4). Finally, Chapter 5 discusses and interprets the results in the context of previous research. In summary, this work establishes that macaques are an excellent animal model for auditory scene analysis and provides new evidence of the cortical response mechanisms during auditory figure-ground segregation. I show that macaques have not only similar detection performance to humans but that the areal organisation measured with fMRI is comparable. Furthermore, I demonstrate robust effects on neuronal firing rates in response to auditory figures across the cortical hierarchy. Lastly, this thesis establishes neuronal differences in figure processing between anterior and posterior auditory cortical fields.