Development of infant ear asymmetries for speech and music

Abstract

Groups of 2-, 3-, and 4-month olds were tested for dichotic ear differences in memory-based phonetic and music timbre discriminations. A right-ear advantage for speech and a left-ear advantage (LEA) for music were found in the 3-and 4-month-olds. However, the 2-month-olds showed only the music LEA, with no reliable evidence of memory-based speech discrimination by either hemisphere. Thus, the responses of all groups to speech contrasts were different from those to music contrasts, but the pattern of the response dichotomy in the youngest group deviated from that found in the older infants. It is suggested that the quality or use of lefthemisphere phonetic memory may change between 2 and 3 months, and that the engagement of right-hemisphere specialized memory for musical timbre may precede that for left-hemisphere phonetic memory. Several directions for future research are suggested to determine whether infant short-term memory asymmetries for speech and music are attributable to acoustic factors, to different modes or strategies in perception, or to structural and dynamic properties of natural sound sources.The existence of a neurobiological dichotomy in human auditory perception, which distinguishes at least some qualities of spoken language from most nonlinguistic auditory events, is strongly implied by the pattern and incidence of functional cerebral asymmetries in adults, particularly as revealed through dichotic ear advantages (e.g.,

The motor theory of speech perception revised

“…This is the ability to sort acoustic patterns into two classes: those that contain (candidate) phonetic structures and those that do not. (For evidence, however indirect, that infants do so sort, see Alegria & Noirot, 1982;Best, Hoffman, & Glanville, 1982;Entus, 1977;Molfese, Freeman, & Palermo, 1975;Segalowitz & Chapman, 1980;Witelson, 1977;but see Vargha-Khadem & Corballis, 1979). To appreciate the bearing of the motor theory on this matter, recall our claim, made in an earlier section, that phonetic objects cannot be perceived as a class by reference to acoustic stigmata, but only by a recognition that the sounds might have been'produced by a vocal tract as it made linguistically significant gestures.…”

Lateral asymmetries in infant melody perception.

“…For example, when sounds were presented directly behind them, neonates were more likely to turn their heads to the right during presentation of speech and to the left during music, suggesting an early lefthemisphere bias for speech perception and right-hemisphere bias for music perception (Young & Gagnon, 1990). In a discrimination task, 3-and 4-month-old infants showed a right-ear advantage for speech syllables and a left-ear advantage for musical notes; 2-month-olds showed only the left-ear advantage for music (Best, Hoffman, & Glanville, 1982).…”

Hand preferences in sign-learning students with autistic disorder

“…In our accounts of the hand preferences of the young deaf and hearing children in the two comparison groups, the children's strong right-hand preference in signing probably reflected a fundamental hemispheric asymmetry for language and sequential motor processing Seal & Bonvillian, 1996). Because signs are both linguistic events and sequential motor actions, a right-hand preference for signing provides evidence of left-cerebral dominance (or lateralisation) for language (Best, Hoffman, & Glanville, 1982;Entus, 1977;Molfese, Freeman, & Palermo, 1975) and for complex motor movements (Heilman, 1979) that emerge in early childhood. Although the autistic students typically made progress in learning to communicate for the first time through signs, their sign learning did not appear to progress as easily or in the same way as that of the two comparison groups.…”