DISCRIMINABILITY and PROTOTYPICALITY of NONNATIVE VOWELS

This study examined how discriminability and prototypicality of nonnative phones modulate the amplitude of the Mismatch Negativity (MMN) event-related brain potential. We hypothesized that if a frequently occurring (standard) stimulus is not prototypical to a listener, a weaker predictive memory trace will be formed and a smaller MMN will be generated for a phonetic deviant, regardless of the discriminability between the standard and deviant stimuli. The MMN amplitudes of Japanese speakers hearing the English vowels/æ/and/α/as standard stimuli and/Λ/as a deviant stimulus in an oddball paradigm were measured. Although the English/æ/-/Λ/contrast was more discriminable than the English/α/-/Λ/contrast for Japanese speakers, when Japanese speakers heard the/æ/standard stimulus (i.e., less prototypical as Japanese/a/) and the/Λ/deviant stimulus, their MMN amplitude was smaller than the one elicited when they heard/α/as a standard stimulus (i.e., more prototypical as Japanese/a/) and/Λ/as a deviant stimulus. The prototypicality of the standard stimuli in listeners' phonological representations modulates the MMN amplitude more robustly than does the discriminability between standard and deviant stimuli.