The decline of cross-species intersensory perception in human infants: underlying mechanisms and its developmental persistence.

The current study investigated the mechanisms underlying the developmental decline in cross-species intersensory matching first reported by Lewkowicz and Ghazanfar [Lewkowicz, D.J., & Ghazanfar, A.A., (2006). The decline of cross-species intersensory perception in human infants. Proc. Natl. Acad. Sci. U. S. A. 103(17), 6771-6774] and whether the decline persists into later development. Experiment 1 investigated whether infants can match monkey vocalizations to asynchronously presented faces and found that neither 4-6 nor 8-10 month-old infants did. Experiment 1 also assessed whether a visual processing deficit may account for the developmental decline in cross-species matching and indicated that it does not because both age groups discriminated silent monkey calls. Experiment 2 investigated whether an auditory processing deficit may account for the decline and indicated that it does not because 8-10 month-old infants discriminated the acoustic versions of the calls. Finally, Experiment 3 asked whether the developmental decline persists into later development by testing cross-species intersensory matching in 12- and 18-month-old infants and showed that it does because neither age group made intersensory matches. Together, these results bolster prior evidence of a decline in cross-species intersensory integration in early human development and shed new light on the mechanisms underlying it.