Neural encoding of vowel formant frequency in normal-hearing listeners

• Published in: The Journal of the Acoustical Society of America Vol. 141; no. 5; p. 3892
• Main Authors: Svirsky, Mario, Won, Jong-Ho, Clinard, Christopher G., Wright, Richard, Sagi, Elad, Tremblay, Kelly
• Format: Journal Article
• Language: English
• Published: 01-05-2017
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.4988733

Physiological correlates of speech acoustics are particularly important to study in humans because it is uncertain whether animals process speech the same way humans do. Studying the physiology of speech processing in humans, however, typically requires the use of noninvasive physiological measures. This is what we attempted in a recent study (Won, Tremblay, Clinard, Wright, Sagi, and Svirsky, JASA 2016) which examined the hypothesis that neural representations of formant frequencies may help predict vowel recognition. To test the hypothesis, the frequency-following response (FFR) and vowel recognition were obtained from 38 normal-hearing listeners using four different vowels. This allowed direct comparisons between behavioral and neural data in the same individuals. FFR was used because it reflects temporal encoding of formant frequencies below about 1500 Hz. Four synthetic vowels with formant frequencies below 1500 Hz were used. Duration was 70 ms for all vowels to eliminate temporal cues and to make identification more difficult. A mathematical model (Sagi et al., JASA 2010) was used to predict vowel confusion matrices based on the neural responses. The mathematical model was successful in predicting good vs poor vowel identification performers based exclusively on physiological data.