Intersensory Redundancy and Infant Selective Attention to Audiovisual Speech

The current study utilized eye-tracking to investigate the effects of intersensory redundancy on infant visual attention and discrimination of a change in prosody in native and non-native audiovisual speech. The Intersensory Redundancy Hypothesis states synchronous and redundant presentation of bimodal stimuli selectively recruits infant attention to and facilitates processing of amodal stimulus properties (Bahrick & Lickliter, 2000). Twelve-month-old monolingual English learning infants viewed either synchronous (redundant) or asynchronous (non-redundant) video clips of a woman speaking in English (native speech) or Spanish (non-native speech). Halfway through each trial, the speaker changed prosody from adult-directed speech (ADS) to infant-directed speech (IDS) or vice versa. Participants completed four 1-min trials, counter-balanced for order. I hypothesized intersensory redundancy would direct infant attention to amodal properties of speech and facilitate discrimination of a change in prosody. Specifically, I predicted infants in the synchronous condition would demonstrate differential scanning of the face based on changes in prosody on both English and Spanish trials. I predicted infants in the asynchronous condition would only demonstrate differential scanning patterns based on a change in prosody on English trials. The analyses revealed a main effect of prosody. Infants focused their visual attention more on the mouth of the speaker on IDS trials in comparison to ADS trials regardless of language or redundancy. There was also an interaction of prosody and language on infants' selective attention. Infants focused more on the nose during English ADS speech in comparison to English IDS speech. These results indicate IDS directs infant attention to the mouth of speakers. In the analysis of detection of a change in prosody, infants in the synchronous condition showed significant differences in looking during the second block of trials depicting English ADS changing to English IDS. This effect may have been due to an interaction of the greater salience of IDS, the infants' extensive experience with their native language, and the facilitating effects of intersensory redundancy for detecting changes in prosody. Overall, these findings exemplify the complexity of development and indicate multiple factors interact to affect infants' visual attention and their ability to discriminate changes in prosody in audiovisual speech.