Training new, nonnative speech contrasts: a comparison of the prototype and perceptual fading techniques

We trained unilingual adult Canadian francophone listeners to identify the English voiceless and voiced linguadental ("th") frictives, /theta/ and /delta/, using synthetic exemplars of each phoneme. Identification training with feedback improved listeners' abilities to identify both natural and synthetic tokens. These results show that training with appropriately selected prototype stimuli can produce a linguistically meaningful improvement in a listener's ability to identify new, nonnative speech sounds--both natural and synthetic. However, it is not yet clear whether such training with a single prototype can improve performance as effectively as the fading technique used by Jamieson and Morosan (1986), since prototype training produced only a moderate improvement in listeners' identifications of synthetic stimuli containing brief frication. Differences between the techniques may reflect the need for listeners to experience the appropriate types of intraphonemic and interphonemic variability during training. Such variability may help to define the category prototype by desensitizing the subjects to differences between exemplars of the same category and by sharpening sensitivity to differences between categories.