title: Slip of the tongue: Implications for evolution and language development.
abstract: A prevailing theory regarding the evolution of language implicates a gestural stage prior to the emergence of speech. In support of a transition of human language from a gestural to a vocal system, articulation of the hands and the tongue are underpinned by overlapping left hemisphere dominant neural regions. Behavioral studies demonstrate that human adults perform sympathetic mouth actions in imitative synchrony with manual actions. Additionally, right-handedness for precision manual actions in children has been correlated with the typical development of language, while a lack of hand bias has been associated with psychopathology. It therefore stands to reason that sympathetic mouth actions during fine precision motor action of the hands may be lateralized. We employed a fine-grained behavioral coding paradigm to provide the first investigation of tongue protrusions in typically developing 4-year old children. Tongue protrusions were investigated across a range of cognitive tasks that required varying degrees of manual action: precision motor action, gross motor action and no motor actions. The rate of tongue protrusions was influenced by the motor requirements of the task and tongue protrusions were significantly right-biased for only precision manual motor action (p<.001). From an evolutionary perspective, tongue protrusions can drive new investigations regarding how an early human communication system transitioned from hand to mouth. From a developmental perspective, the present study may serve to reveal patterns of tongue protrusions during the motor development of typically developing children.
authors.affiliation: Department of Psychology, Faculty of Science and Technology, University of Westminster, 115 New Cavendish Street, London, England W1W 6UW, UK. Electronic address: g.forrester@westminster.ac.uk.
authors.forename: Gillian S
authors.initials: GS
authors.lastname: Forrester
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London, Faculty of Medicine, St Mary's Campus, Norfolk Place, Paddington, London, England W2 1PG, UK; Department of Psychology, Mid Sweden University, Östersund, Sweden. Electronic address: a.rodriguez@imperial.ac.uk.
authors.forename: Alina
authors.initials: A
authors.lastname: Rodriguez
mesh_terms: D005075:Biological Evolution; D002657:Child Development / Q000502:physiology*; D002675:Child, Preschool; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D007802:Language; D007804:Language Development; D008297:Male; D011597:Psychomotor Performance / Q000502:physiology*; D014059:Tongue / Q000502:physiology*
keywords: Cerebral lateralization; Language; Tongue; Typically developing children