Visual discrimination of vowel duration

Discrimination of vowel duration was explored with regard to discrimination threshold, error bias, and effects of modality and consonant context. A total of 122 normal-hearing participants were presented with disyllabic-like items such as /lal-lal/ or /mam-mam/ in which the lengths of the vowels were systematically varied and were asked to judge whether the first or second vowel was longer. Presentation was either visual, auditory, or audiovisual. Vowel duration differences varied in 24 steps: 12 with a longer first /a/ and 12 with a longer last /a/ (range: ±33–400 ms). Results: 50% JNDs were smaller than the lowest tested step size (33 ms); 75% JNDs were in the 33–66 ms range for all conditions but V /lal/, with a 75% JND at 66–100 ms. Errors were greatest for visual presentation and for /lal-lal/ tokens. There was an error bias towards reporting the first vowel as longer, and this was strongest for /mam-mam/ and when both vowels were short, possibly reflecting a sublinguistic processing strategy.