Date of Award

2003

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Psychology

Supervisor

Dr. Laurel J. Trainor

Abstract

Timbre, or sound quality, is important for the identification of objects, speech sounds, people, and the vocal expression of emotion. One important cue to timbre is the spectral envelope, representing the change in intensity across frequency. Spectral slope is the linear component of the spectral envelope. Very little is known about infants' perception of timbre. However, adults are highly sensitive to very small changes in spectral shape (e.g., Green, 1992), and spectral slope is an important cue for identifying perceptual constancies in sound (Li & Pastore, 1995). Previous studies have established that infants can discriminate large differences in spectral shape (e.g., Trehub, Endman, & Thorpe, 1990; Clarkson, 1995). This thesis extends this literature by systematically examining the role of spectral slope in timbre discrimination using steady-state complex tones. The studies presented here support the idea that both infants and adults use global spectral characteristics, such as spectral slope, as a basis for timbre discrimination. The results show that 8-month-old infants are best able to discriminate spectral slope differences in sounds with moderately negative spectral slopes in the range of speech and musical sounds. Furthermore, infants show an attentional bias for sounds with slopes in this range. This thesis also demonstrates that there is a progression in the development of sensitivity to spectral slope, with initial ability to discriminate spectral slope emerging around 5 months of age. Finally, this thesis shows that spectral slope discrimination is better in adults than in infants, but that adults are similar to infants in that they are also more sensitive to spectral slopes in the moderately negative range.

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