Infant and adult ear asymmetry differences for memory‐based consonant versus vowel discriminations

Abstract

Recent evidence indicates that the adult REA for speech and LEA for music are present by 3 months. Yet the nature of perceptual asymmetries, and the effect of stimulus properties, in the infants' speech REA are unknown. The adult literature on perceptual asymmetrics suggests a possible left hemisphere mechanism for perception of consonants via reference to rapid articulatory gestures, since adults typically show REAs for consonants but not for vowels. Condition A of this study measured infant and adult ear asymmetries for discriminations among consonants versus vowels in CV syllables. Studies of associations between stimulus properties and adult ear asymmetries indicate special left hemisphere responsivity to transient information, e.g., rapid formant transitions. Therefore, Condition B assessed how removal of formant transitions from the CVs (phonemes remained identifiable) affected infant and adult ear asymmetries for consonant versus vowel discriminations. Results indicate adult asymmetries are largely perceptual, with left hemisphere phonetic perception for consonants but not vowels. However, acoustic factors apparently outweigh phonetic perceptual factors in infant speech REAs. Implications for brain‐behavior relationships in perceptual development, especially speech perception, will be discussed. [Partially supported by NICHD and NINCDS.]