Discrimination of subphonemic phonetic distinctions

Seven native speakers of Thai and seven native speakers of English took part in a set of discrimination experiments. The Thai‐speaking subjects took part in discrimination tests of both labial and velar stimuli which varied along voice onset time continua. The English‐speaking subjects took part only in the velar discrimination test. The Thai language makes phonemic distinctions between voiced and voiceless unaspirated stops at the labial and dental places of articulation. However, Thai does not make a distinction between voiced and voiceless unaspirated velars. English does not make this distinction at any place of articulation. Therefore, the Thai velar discrimination functions can be compared both with discrimination functions in which a phonemic distinction is made between voiced and voiceless unaspirated stimuli and also with the English‐speaking subjects' discrimination functions where no such phonemic distinction exists in the language. The English‐speaking subjects' discrimination functions are characterized by a single peak spanning the phoneme boundary. The Thai‐speaking subjects' labial discrimination functions are characterized by a large peak spanning each phoneme boundary. Their velar discrimination functions are characterized by a large peak spanning the phoneme boundary and a smaller peak spanning the subphonemic but systematically relevant phonetic boundary.