| Summary: | Myriad factors influence perceptual processing, but “embodied” approaches assert that sensorimotor information about bodily movements plays an especially critical role. This view has precedence in speech research, where it has often been assumed that the movements of one’s articulators (i.e., the tongue, lips, jaw, etc.) are closely related to perceiving speech. Indeed, previous work has shown that speech perception is influenced by concurrent stimulation of speech motor cortex or by silently making articulatory motions (e.g., mouthing “pa”) when hearing speech sounds. Critics of embodied approaches claim instead that so-called articulatory influences are attributed to other processes (e.g., auditory imagery or feedback from phonological categories), which are also activated when making speech articulations. This dissertation explores the embodied basis of speech perception, and further investigates its ontogenetic development. Chapter 2 reports a study where adults made silent and synchronous speech-like articulations while listening to and identifying speech sounds. Results show that sensorimotor aspects of these movements (i.e., articulatory-motor information) are a robust source of perceptual modulation, independent from auditory imagery or phonological activation. Chapter 3 reports that even low-level, non-speech articulatory-motor information (i.e., holding one’s breath at a particular position in the vocal tract) can exert a subtle influence on adults’ perception of related speech sounds. Chapter 4 investigates the developmental origins of these influences, showing that low-level articulatory information can influence 4.5-month-old infants’ audiovisual speech perception. Specifically, achieving lip-shapes related to /i/ and /u/ vowels (while chewing or sucking, respectively) is shown to disrupt infants’ ability to match auditory speech information about these vowels to visual displays of talking faces. Together, these chapters show that aspects of speech processing are embodied and follow a pattern of differentiation in development. Before infants produce clear speech, links between low-level articulatory representations and speech perception are already in place. As adults, these links become more specific to sensorimotor information in dynamically coordinated articulations, but vestigial links to low-level articulatory-motor information remain from infancy.
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