Stimulus Variability and Perceptual Learning of Nonnative Vowel Categories

English-speakers' learning of a French vowel contrast (/schwa/-/slashed o/) was examined under six different stimulus conditions in which contrastive and noncontrastive stimulus dimensions were varied orthogonally to each other. The distribution of contrastive cues was varied across training conditions to create single prototype, variable far (from the category boundary), and variable close (to the boundary) conditions, each in a single talker or a multiple talker version. The control condition involved identification of gender appropriate grammatical elements. Pre- and posttraining measures of vowel perception and production were obtained from each participant. When assessing pre- to posttraining changes in the slope of the identification functions, statistically significant training effects were observed in the multiple voice far and multiple voice close conditions.