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Infants' perception of the audible, visible and bimodal attributes of talking and singing faces

Human faces and accompanying voices are a ubiquitous part of the infant’s perceptual experience. They serve as a major vehicle for the acquisition of linguistic, social, and emotional skills, just to name a few. Therefore, the study of how infants perceive the audible, visible and combined attributes of face/voice compounds can show how various features of face/voice compounds contribute to the acquisition of higher-level skills. I review the findings from a series of studies in which we investigated infants’ response to a variety of features of face/voice compounds. These findings show that there are important developmental differences in the way infants respond to the audible, visible and bimodal components of face/voice compounds and that these differences are dependent on the specific nature of the information given. Overall, the results suggest that infants, like adults, may respond to multiple sources of information when attempting to evaluate the “message” carried by bimodal speech but that their functional use of this information is limited by the infant’s developmental status. 1. ISSUES AND QUESTIONS Talking or singing faces are relatively ubiquitous in infants’ daily lives. From a perceptual point of view, they provide a set of complex and hierarchically organized features that must somehow be perceived to get to the “message.” One way to get to the message is to integrate the diverse auditory and visual sources of information into unified objects/events. By integrating these heteromodal sources of information, the perceiver no longer merely perceives a collection of diverse, heteromodal features. As a result, perception is more efficient, easier, and more adaptive. In general, intermodal integration is a process that makes it possible for the perceptual system to relate two or more heteromodal inputs. Integration can include one of three distinct kinds of processes: (a) nonspecific effects of stimulation in one modality on responsiveneness to stimulation in a different modality, (b) matching of equivalent heteromodal features such as intensity or overall temporal rhythm (also known as amodal perception), or (c) association of modality-specific attributes (e.g., the timbre of a person’s voice and the configuration of their face). It should be noted that this definition of integration differs from the way some writers define intermodal integration, particularly when referring to bimodal speech perception. For example, for Burnham [1] integration refers to the fusion of the audible and visible attributes of linguistic information, often resulting in a new percept (see discussion of the McGurk effect in Section 2). Because the principal aim of the current article is to place the work on infants’ response to talking and singing faces in a broader intermodal perception framework, the definition of integration offered here will be used. In order to integrate the cues inherent in talking and singing faces, infants must rely on their sensory, perceptual, and cognitive skills. These skills are relatively limited in early human development by the fact that the auditory and visual modalities are immature at birth and that sensory, perceptual, and cognitive processes undergo significant developmental changes and re-organization during infancy [2-4]. Complicating the picture further is the fact that the structural and functional development of the different sensory systems does not occur all at the same time. Although the development of all the sensory systems begins during the prenatal period, the somesthetic/vestibular modality is the first to develop, followed in order by the chemical, the auditory, and the visual modalities [5]. This sequential functional onset of the sensory systems means that at birth each sensory system starts out life with a different experiential history and this is likely to have a major impact on subsequent postnatal perceptual development and differentiation. This, in turn, may mean that integration of heteromodal sources of input may be more or less difficult at a given point in development depending both on the type of experience that the specific modality might have had up to that point and on the extent of its structural and functional maturity. ! ISCA Archive