Cerebral dominance for pitch contrasts in tone language speakers and in musically untrained and trained English speakers

Speakers of a tone language, Thai, recognize pitch contrasts which are linguistically significant in their language better at the right ear in a dichotic listening task, but show no ear advantage for the same pitch contrasts occurring in a nonlinguistic context. American English speakers, divided into musically untrained and trained groups, show no ear advantage for those same pitch contrasts. The only eff ect of musical training is an enhancement of left ear accuracy for pitch contrast recognition. A large number of studies on cerebral function have investigated left and right hemi­ spheric specialization (Mountcastle, 1962; Bogen, 1969; Dimond, 1972; Dimond & Beaumont, 1974; Schmitt & Worden, 1974). For auditory stimuli, some researchers have asked whether lateralization to one cerebral hemisphere is based on acoustic features or on the functional context of the stimulus. Normal humans can be tested by dichotic listening (Berlin, Lowe-Bell, Cullen & Thompson, I 973; Cutting, I 973; Van Lancker, 1975), in which a subject hears two different, simultaneous sounds (one at each ear). The subject typically makes errors in reporting what he or she hears. These errors are greater at one or the other ear, depending on the type of stimulus. Because of stronger contralateral con­ nections (than ipsilateral) between ear and hemisphere, a "right ear advantage" (higher accuracy at the right ear than the left) is assumed to indicate preferential processing by the left hemisphere, and vice versa. Such findings for many diverse stimuli have contributed to hypotheses on hemispheric specialization. Most dichotic listening results have suggested that the functional context of a given stimulus predicts ear advantage. For example, if a stimulus is perceived as part of the linguistic system native to the subject, then those stimuli are more accurately heard at the right ear. In one study, vowels in syllables yielded a right ear advantage, whereas the same sounds embedded in a nonlinguistic context yielded a left ear advantage (Spellacy & Blumstein, 1970). Environmental sounds (Chaney & Webster, 1966; Curry, 1967), and some musical stimuli (Gordon, 1970) have shown a left ear advantage. These data support the "functional" theory of hemispheric specialization for processing auditory (and visual and other) stimuli. Our experiments on Thai tones strongly confirm the functional theory of hemispheric specialization. In the first experiment (Van Lancker & Fromkin, 1973), we found that pitch contrasts were better identified at the right ear when constituting the tone contrasts of a tone language (Thai), but not when presented (to the same subjects) as hums. ln a tone language, pitch alone may contrast the meanings of words which are otherwise identical 20 D. Van Lancker and V. A. Fromkin in sounds. In a non-tone language, such as English, pitch is used to convey information (e.g. the intonation of an interrogative sentence will differ from that of a declarative) but the meaning of"cat" will remain the same whether it is produced with a high, medium, low, rising or falling pitch in a sentence such as "The cat is on the mat". In Thai, however ( or in languages such as Chinese, Twi, Hausa, etc.) a word like "naa" will mean different things depending on the pitch (see Table I). Table I Three sets of stimuli used Stimulus Tone Length (ms) English gloss