Training native English speakers to identify Japanese vowel length contrast with sentences at varied speaking rates.

Native English speakers were trained to identify Japanese vowel length in three types of training differing in sentential speaking rate: slow-only, fast-only, and slow-fast. Following Pisoni and Lively's high phonetic variability hypothesis [Pisoni, D. B., and Lively, S. E., Speech Perception and Linguistic Experience, 433-459 (1995)], higher stimulus variability by means of training with two rates was hypothesized to aid learners in adapting to speech rate variation more effectively than training with only one rate. Trained participants identified the length of the second vowel of disyllables, short or long, embedded in a sentence of the respective rate, and received immediate feedback. The three trained groups' abilities before and after training were examined with tests containing sentences of slow, normal, and fast rates, and were compared with those of a control that was not trained. A robust effect of slow-fast training, a marginal effect of slow-only training, but no significant effect of fast-only training were found in the overall test scores. Slow-fast and slow-only training showed small advantages over fast-only training on the fast-rate test scores, while effects for all three training types were found on the slow- and normal-rate test scores. The degree to which the results support the high phonetic variability hypothesis is discussed.