Contribution of F0 and phonation to tone perception in the Zaiwa language

Previous research on categorical perception of tone has primarily examined the influence of fundamental frequency (F0), while the role of phonation, though increasingly studied, remains underexplored. This study investigates the role of phonation and how it interacts with F0 cues in tone perception, using the Zaiwa language as a case study. Specifically, we examine the categorical perception of Tone 44 (produced with a pressed voice) and Tone 35 (produced with a modal voice). To achieve this, we first conducted an acoustic analysis of the Zaiwa tone system, which forms the basis for our novel method of speech synthesis. Using this method, we created six tonal continua between Tone 44 and Tone 35 by systematically modifying F0 alone, phonation alone, and both simultaneously. Native Zaiwa speakers then participated in an experiment using the categorical perception paradigm with these synthesized continua. The results indicate that the participants were unable to distinguish the phonemic categories of the two tones when only phonation was modified. While modifying F0 alone allowed for tone distinction, participants’ perception followed a continuous pattern. However, when both F0 and phonation were modified simultaneously, participants accurately identified the phonemic categories of tones and perceived the continuum between the two tones categorically. These findings suggest that both F0 and phonation serve as perceptual cues for distinguishing Tone 44 and Tone 35 in Zaiwa, with F0 as the primary cue and phonation as a secondary cue. However, phonation remains crucial, as its absence weakens the categorical perception of these tones.