An investigation of spatial representations of pitch in individuals with congenital amusia

Congenital amusia, a disorder that affects individuals' musical abilities, has been widely investigated over the past dozen years. Although considerable progress has been made in understanding the psychophysical characteristics and the neural mechanisms of congenital amusia, most is based on the evidence coming from studies that focus primarily on the auditory modality. In this thesis, I explore the relationship between music perception and visuospatial features in individuals with congenital amusia. Chapter 1 reviews existing theory and evidence concerning spatial representations of music, and Chapter 2 provides the background knowledge about congenital amusia and outlines the experimental work that is included in the thesis. In Chapter 3, I describe two experiments on spatial representations of pitch in amusia using a stimulus-response compatibility paradigm. The results confirm that amusic individuals represent pitch with a vertical dimension. Chapter 4 describes new empirical evidence that the perceived magnitude of supra-threshold pitch changes is equivalent for amusic and non-amusic individuals, contrary to what one might expect. In Chapter 5, I investigate whether the impairment observed in contour processing exhibited by amusic individuals is caused by a failure in pitch change direction identification, or whether it arises from poor pitch memory. To disentangle these two stages of contour processing, a novel Self-paced Audio-visual Contour Task was devised. Compared with non-amusic participants, amusics exhibited reduced sensitivity to audio-visual incongruence of the direction of change in pitch and vertical space. This reduced sensitivity reflects a failure to consciously access a spatial representation of pitch. In Chapter 6, I used EEG to measure the extent to which visuospatial information influences amusic individual's judgement of pitch change direction. The behavioural and ERP results show that the influence of visual information is significantly greater for amusic individuals than for non-amusic individuals, suggesting that amusics focused strongly on visual information to complete the auditory task. In Chapter 7, I summarise these findings and argue that amusic individuals have an unstable spatial representation of pitch, which has cascade effects that lead to high-level musical impairments. However, they also draw upon spatial information from the visual modality to clarify or reinforce their auditory representations. As such, visuospatial cues have potential to help amusic individuals understand and perceive music more precisely.