Changes to perceptual assimilation following training

Adult speakers of American-English have difficulty perceiving front-back rounding contrasts in vowels, such as French /œ/-/o/. These difficulties stem in part from how learners map sounds in a second language onto native-language sound categories. We used a perceptual-assimilation task to test how perceptual training changes listeners’ mapping of nonnative speech sounds. One listener group was trained with a bimodal distribution of stimuli drawn from an /œ/-/o/ acoustic continuum, a second was trained with a unimodal distribution, and a third (control) group completed no training. The training incorporated active learning with feedback and lexical support. In the assimilation task, listeners heard French vowels and were asked to select which of eight English /hVd/ words best matched the French stimulus. Results revealed general perceptual training effects and differences in both trained groups. For /o/, both trained groups differed significantly from untrained controls. However, for /œ/, listeners in the unimodal group did not differ from the untrained controls, but the bimodal group differed from the untrained controls. Thus, exposure to a unimodal distribution can alter perception, but a bimodal distribution may have stronger effects on perception. Bimodal distribution may be better for facilitating assimilation of nonnative sounds to native-like categories.