The development of infants' sensitivity to native versus non-native rhythm.

Speech rhythm is considered one of the first windows into the native language, and the taxonomy of rhythm classes is commonly used to explain early language discrimination. Relying on formal rhythm classification is problematic for two reasons. First, it is not known to which extent infants' sensitivity to language variation is attributable to rhythm alone, and second, it is not known how infants discriminate languages not classified in any of the putative rhythm classes. Employing a central-fixation preference paradigm with natural stimuli, this study tested whether infants differentially attend to native versus nonnative varieties that differ only in temporal rhythm cues, and both of which are rhythmically unclassified. An analysis of total looking time did not detect any rhythm preferences at any age. First-look duration, arguably more closely reflecting infants' underlying perceptual sensitivities, indicated age-specific preferences for native versus non-native rhythm: 4-month-olds seemed to prefer the native-, and 6-month-olds the non-native language-variety. These findings suggest that infants indeed acquire native rhythm cues rather early, by the 4th month, supporting the theory that rhythm can bootstrap further language development. Our data on infants' processing of rhythmically unclassified languages suggest that formal rhythm classification does not determine infants' ability to discriminate language varieties.