Infants' perception of the audible, visible, and bimodal attributes of multimodal syllables.

Three experiments investigated 4-, 6-, and 8-month-old infants' perception of the audible, visible, and combined attributes of bimodally specified syllables. Ninety-six infants in each experiment were habituated to a person mouthing and uttering a syllable and then tested for detection of changes of either the audible, visible, or combined attributes of the syllable. When the attributes of the syllable were produced in an adult-directed manner, all three age groups discriminated the audible and bimodal attribute changes but only the 8-month-olds discriminated the visible one. When the difference between the familiar and novel attributes of the syllable was enhanced by testing with a novel syllable produced in an infant-directed manner, all three age groups detected all three types of changes. Finally, to test the possible role of audiovisual synchrony in responsiveness, infants were tested with an asynchronous syllable spoken either by the same person or by a novel person following habituation to a synchronous syllable. Results suggested that at four months infants attended primarily to the featural information, at six months primarily to the asynchrony, and at eight months to both features independently. These results help identify some of the important dimensions of multimodal speech during early development.