Abstract
Theoretical models of speech production suggest that the speech motor system (SMS) uses auditory goals to determine errors in its auditory output during vowel production. This type of error calculation indicates that within-speaker production variability of a given vowel is related to the size of the vowel’s auditory goal. However, emerging evidence suggests that the SMS may also take into account perceptual knowledge of vowel categories (in addition to auditory goals) to estimate errors in auditory feedback. In this study, we examined how this mechanism influences within-speaker variability in vowel production. We conducted a study (n = 40 adults), consisting of a vowel categorization task and a vowel production task. The vowel categorization task was designed—based on participant-specific vowels—to estimate the categorical perceptual boundary (CPB) between two front vowels (/ε/ and /æ/). Using the vowel production data of each participant, we calculated a variability-based boundary (VBB) located at the “center of mass” of the two vowels. The inverse of the standard deviation of a vowel distribution was used as the “mass” of the vowel. We found that: (a) categorical boundary was located farther from more variable vowels; and (b) the calculated VBB (i.e., the center of mass of the vowels) significantly and positively correlated with the estimated categorical boundary (r = 0.912 for formants calculated in hertz; r = 0.854 for formants calculated in bark). Overall, our findings support a view that vowel production and vowel perception are strongly and bidirectionally linked.
Highlights
A large body of literature indicates that the speech production and speech perception systems interact in many intricate ways (Galantucci et al, 2006; Guenther, 2006; Tatham and Morton, 2006; Hickok, 2012; Perkell, 2012)
In an analogy to physics, two adjacent vowels can be considered two connected masses, and the ‘‘mass’’ of each vowel can be determined by the inverse of the variability of the vowel distribution
We examined whether the perception of two adjacent vowels interacts with the production variabilities of the two vowels
Summary
A large body of literature indicates that the speech production and speech perception systems interact in many intricate ways (Galantucci et al, 2006; Guenther, 2006; Tatham and Morton, 2006; Hickok, 2012; Perkell, 2012). The exact nature of the speech goals is unclear, it has been suggested that the speech motor system (SMS) may use perceptual goals (e.g., auditory goals) to determine errors in its motor output (Perkell et al, 1997, 2008; Perkell, 2012; Guenther, 2016) These models posit that during production, the SMS compares auditory feedback of the produced speech with its auditory goals; when the auditory feedback resides outside the auditory goals (i.e., auditory error), the SMS generates corrective motor responses to reduce the perceived error. In a speech discrimination task, speakers are asked to discriminate between speech sounds with subtle acoustic differences; discrimination tasks measure speakers’ ability to distinguish small changes in auditory input (i.e., auditory acuity) In support of this prediction, a few studies have examined the relationship between auditory acuity and vowel production (Perkell et al, 2004a, 2008; Franken et al, 2017). These studies have shown that speakers with better auditory acuity—typically interpreted as smaller auditory goals regions—produce more consistent vowels (i.e., smaller within-vowel variability)
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