Five-month-old infants discrimination of unfamiliar languages does not accord with "rhythm class"

Young infants are sensitive to prosody, which they use to distinguish between speakers and between languages. Indeed, patterns of language discrimination have been interpreted as supporting a “rhythm class” typology, where the rhythmic nature of earliest language exposure determines the primary perceptual units of speech segmentation. In previous studies, five-month-old infants discriminated languages from different putative rhythm classes, but only within a class where one or both languages are familiar. Thus, English infants did not distinguish “syllable-timed” Italian and Spanish, nor “stresstimed” Dutch and German, but Spanish infants distinguished “syllable-timed” Catalan and Spanish. In three head-turn preference experiments, we tested whether English fivemonth-olds could discriminate – pairwise – between French, Spanish and Finnish. Although all have been categorized as “syllable-timed”, they differ in their realization and distribution of strong syllables. In each experiment, we familiarized infants to one of two languages and then exposed them to new speakers from the same or the other language. With French and Spanish, infants looked longer to the new language than the familiar one, indicating discrimination. They failed, however, to discriminate French/Finnish or Spanish/Finnish. These results strongly suggest that – rather than sensitivity to discrete classes – discrimination reflects exploitation of gradient prosodic differences.