This research examined the developmental course of infants' ability to perceive affect in bimodal (audiovisual) and unimodal (auditory and visual) displays of a woman speaking. According to the intersensory redundancy hypothesis (L. E. Bahrick, R. Lickliter, & R. , detection of amodal properties is facilitated in multimodal stimulation and attenuated in unimodal stimulation. Later in development, however, attention becomes more flexible, and amodal properties can be perceived in both multimodal and unimodal stimulation. The authors tested these predictions by assessing 3-, 4-, 5-, and 7-month-olds' discrimination of affect. Results demonstrated that in bimodal stimulation, discrimination of affect emerged by 4 months and remained stable across age. However, in unimodal stimulation, detection of affect emerged gradually, with sensitivity to auditory stimulation emerging at 5 months and visual stimulation at 7 months. Further temporal synchrony between faces and voices was necessary for younger infants' discrimination of affect. Across development, infants first perceive affect in multimodal stimulation through detecting amodal properties, and later their perception of affect is extended to unimodal auditory and visual stimulation. Implications for social development, including joint attention and social referencing, are considered. Keywords infant perception; intersensory redundancy; intersensory perception; multimodal perception; emotion perception Young infants and adults perceive a world of unitary and cohesive objects and events even though they encounter a continuously changing array of visual, auditory, olfactory, gustatory, and tactile stimulation. The information available to the sensory systems that specifies properties of objects and events is of two kinds: amodal and modality specific. Amodal information (e.g., texture, rhythm, tempo, and intensity) is not specific to one sense modality as it can be conveyed redundantly across multiple sense modalities (J. J. Gibson, 1966Gibson, , 1979. In contrast, information that is modality specific (e.g., color, visual pattern, pitch, etc.) is specific to a single sense modality and cannot be conveyed redundantly across multiple sense modalities. Most events, such as a bouncing ball, provide both modality-specific and amodal information. That is, the ball provides color and pattern information that can only be specified visually and amodal information such as the tempo and rhythm of the bounces that can be redundantly specified in acoustic as well as visual stimulation.Correspondence concerning this article should be sent to Ross Flom, Department of Psychology, Brigham Young University, Provo, UT 84602. E-mail: E-mail: flom@byu.edu. A portion of these data was presented at the Society for Research in Child Development, Tampa, Florida, April 2003. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptResearchers have demonstrated that one of the earliest and perhaps most important perceptual competencies is infants' sen...

That the senses provide overlapping information for objects and events is no extravagance of nature. This overlap facilitates attention to critical aspects of sensory stimulation, those that are redundantly specified, and attenuates attention to nonredundantly specified stimulus properties. This selective attention is most pronounced in infancy and gives initial advantage to the perceptual processing of, learning of, and memory for stimulus properties that are redundant, or amodal (e.g., synchrony, rhythm, and intensity), at the expense of modality-specific properties (e.g., color, pitch, and timbre) that can be perceived through only one sense. We review evidence supporting this hypothesis and discuss its implications for theories of perceptual, cognitive, and social development.

L. Bahrick and R. Lickliter (2000) proposed an intersensory redundancy hypothesis that states that information presented redundantly and in temporal synchrony across two or more sensory modalities selectively recruits infant attention and facilitates perceptual learning more effectively than does the same information presented unimodally. In support of this view, they found that 5-month-old infants were able to differentiate between two complex rhythms when they were presented bimodally, but not unimodally. The present study extended our test of the intersensory redundancy hypothesis to younger infants and to a different amodal property. Three-month-olds' sensitivity to the amodal property of tempo was investigated. Results replicated and extended those of Bahrick and Lickliter, demonstrating that infants could discriminate a change in tempo following bimodal, but not unimodal, habituation. It appears that when infants are first learning to differentiate an amodal stimulus property, discrimination is facilitated by intersensory redundancy and attenuated under conditions of unimodal stimulation.

Factors affecting joint visual attention in 12- and 18-month-olds were investigated. In Experiment 1 infants responded to 1 of 3 parental gestures: looking, looking and pointing, or looking, pointing, and verbalizing. Target objects were either identical to or distinctive from distractor objects. Targets were in front of or behind the infant to test G. E. Butterworth's (1991b) hypothesis that 12-month-olds do not follow gaze to objects behind them. Pointing elicited more episodes of joint visual attention than looking alone. Distinctive targets elicited more episodes of joint visual attention than identical targets. Although infants most reliably followed gestures to targets in front of them, even 12-month-olds followed gestures to targets behind them. In Experiment 2 parents were rotated so that the magnitude of their head turns to fixate front and back targets was equivalent. Infants looked more at front than at back targets, but there was also an effect of magnitude of head turn. Infants' relative neglect of back targets is partly due to the "size" of adult's gesture.

This study examined the development of infants' ability to perceive, learn, and remember the unique face-voice relations of unfamiliar adults. Infants of 2, 4, and 6 months were habituated to the faces and voices of 2 same-gender adults speaking and then received test trials where the faces and voices were synchronized yet mismatched. Results indicated that 4- and 6-month-olds, but not 2-month-olds, detected the change in face-voice pairings. Two-month-olds did, however, discriminate among the faces and voices in a control study. Results of a subsequent intermodal matching procedure indicated that only the 6-month-olds showed matching and memory for the face-voice relations. These findings suggest that infants' ability to detect the arbitrary relations between specific faces and voices of unfamiliar adults emerges between 2 and 4 months of age, whereas matching and memory for these relations emerges somewhat later, perhaps between 4 and 6 months of age.