Left-Hemisphere Advantage for Click Consonants is Determined by Linguistic Significance and Experience

Abstract

Left-hemisphere (LH) superiority for speech perception is a fundamental neurocognitive aspect of language, and is particularly strong for consonant perception. Two key theoretical aspects of the LH advantage for consonants remain controversial, however: the processing mode (auditory vs. linguistic) and the developmental basis of the specialization (innate vs. experience dependent). Click consonants offer a unique opportunity to evaluate these theoretical issues. Brief and spectrally complex, oral clicks exemplify the acoustic properties that have been proposed for an auditorily based LH specialization, yet they retain linguistic significance only for listeners whose languages employ them as consonants (e.g., Zulu). Speakers of other languages (e.g., English) perceive these clicks as nonspeech sounds. We assessed Zulu versus English listeners' hemispheric asymmetries for clicks, in and out of syllable context, in a dichotic-listening task. Performance was good for both groups, but only Zulus showed an LH advantage. Thus, linguistic processing and experience both appear to be crucial.