Rastatter M, Sullivan J
Percept Mot Skills. 1986 Feb;62(1):133-4. doi: 10.2466/pms.1986.62.1.133.
Coefficients of variation of EMG signals from the orbicularis oris superior, orbicularis oris inferior, and masseter muscles of normal 4- and 8-yr.-olds and adults and of articulatory disordered 8-yr.-olds suggests that development of speech motor equivalence is individualized, muscle-dependent, and affects all children. Age-related differences were noted. Group data did not predict individual values.