Great expectations! How predictions about the magnitude of a forthcoming sound affect its perceptual and neural processing

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Copyright: Libesman, Sol
Psychoacoustic research has primarily examined how the low-level properties of auditory waveforms influence perceived loudness. However, we often experience auditory events not in isolation, but accompanied by characteristic visual information. Despite this, the influence of vision on perceived loudness has rarely been considered. The intensity of an auditory signal at-the-ear depends on both the power of the sound source and the distance of the source from the listener. The aim of this thesis was to explore whether visual cues relaying information about these two factors influence perceived loudness. After providing an Introduction and Background to this thesis, Chapters 3 and 4 assessed whether visual cues that disambiguate the distance of a sound source influenced perceived loudness. These studies simulated a loudspeaker relaying sounds at different distances in either anechoic or reverberant conditions and extracted loudness judgements using a 2-interval forced-choice task. The findings of both chapters indicated that visual distance information was not exploited to disambiguate the loudness of an auditory event. Chapters 5 and 6 assessed whether visual information about the power of a sound source influenced the perception of loudness and the neurophysiological coding of auditory intensity. In both chapters visual information about the power of the sound source was provided with videos depicting a 'strong' and a 'weak' hand-clap. Chapter 5 employed a novel 2-pair forced-choice task to extract participants' loudness estimates. The results indicated that clap sounds that were paired with the 'strong' clap video were amplified in loudness relative to the 'weak' clap video. Chapter 6 used electroencaphalography (EEG) to test whether visual cues to sound source power are capable of altering the neurophysiological response to auditory stimulation. We found that when participants received identical auditory input, the 'strong' clap video evoked an increased auditory response relative to the 'weak' clap video. Chapters 5 and 6 provide evidence that the neurological and subjective coding of auditory intensity is influenced in accordance with the visually created expectation. Taken together, the findings of this thesis demonstrate that perceived loudness is dependent not only on auditory input per se, but also on higher-level predictions about the expected intensity of an auditory event.
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Libesman, Sol
Whitford, Thomas
Damien, Mannion
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PhD Doctorate
UNSW Faculty
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