Perceptual boundary of vowel quantity: a perceptual study of synthesized Arabic vowels

This study investigates how native speakers of Najdi and Cairene Arabic perceive the contrast between short and long vowels, focusing on the role of vowel duration. Forty participants (20 per dialect) completed a forced-choice identification task using synthesized minimal pairs with systematically varied vowel durations. Mixed-effects logistic regression models were used to analyze how duration and dialect influenced responses. Duration was a strong predictor of “long” responses across all vowel pairs, but sensitivity to duration varied by dialect and vowel. For [i], Cairene listeners categorized vowels as “long” at shorter durations (84 ms) and showed steeper perceptual slopes than Najdi listeners, who required longer durations (96 ms) and had more gradual responses. For [a], both dialects showed a shared boundary at 101 ms, though Cairene speakers again responded more categorically. For [u], boundary differences were small (Najdi = 100 ms, Cairene = 110 ms) and not statistically significant. These findings suggest that while Arabic speakers rely on duration to distinguish vowel quantity, perceptual calibration is influenced by dialect and vowel quality. The study highlights the value of controlled synthesis and mixed-effects modeling for examining subtle variation in phonemic perception across dialects.