Date of Degree

6-2014

Document Type

Capstone Project

Degree Name

Au.D.

Program

Audiology

Advisor(s)

Brett A. Martin

Subject Categories

Speech Pathology and Audiology

Keywords

fricative, secondary cues, acoustic change complex, trading relations, event-related potential, acoustic salience, perceptual weight, spectral prominence, evoked potential

Abstract

The primary cue used by normal hearing individuals for identification of the fricatives /s/ and /ʃ/ is the most prominent spectrum of frication, which is discrete for this fricative contrast. Secondary cues that influence the identification and discrimination of these fricatives are context dependent. Specifically, the secondary cues that have been found to most significantly impact fricative perception include (a) the second formant transition onset and offset frequencies of a fricative-vowel pair, and (b) the amplitude of the spectral peak in the 2500Hz region of frication relative to an adjacent vowel’s peak amplitude in the same frequency region. However, the perceptual weight placed on each of these secondary cues remains unclear. Some research suggests that normal hearing individuals place equal weight on these secondary cues, while others posit that individuals have different cue preferences. In addition, salience of these secondary cues, which is dependent upon encoding of audibility, has yet to be assessed objectively in previous studies. The current study assessed the perceptual weight of these two secondary acoustic cues for the place of articulation fricative contrast /s/ vs. /ʃ/ while also objectively indexing the salience of each cue in normal hearing adults by utilizing a behavioral trading relations paradigm and an electrophysiological measure of acoustic change, respectively. Normal hearing adults were found to rely more heavily on the relative amplitude comparison cue relative to the formant frequency transition cue. Electrophysiological responses to secondary cues suggested that, for the most part, salience is driving the amplitude cue dominance.

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