Purpose: Current models of speech development argue for an early link between speech production and perception in infants. Recent data show that young infants (at 4-6 months) preferentially attend to speech sounds (vowels) with infant vocal properties compared to those with adult vocal properties, suggesting the presence of special "memory banks" for one's own nascent speech-like productions. This study investigated whether the vocal resonances (formants) of the infant vocal tract are sufficient to elicit this preference and whether this perceptual bias changes with age and emerging vocal production skills.
Method: We selectively manipulated the fundamental frequency (f0 ) of vowels synthesized with formants specifying either an infant or adult vocal tract, and then tested the effects of those manipulations on the listening preferences of infants who were slightly older than those previously tested (at 6-8 months).
Results: Unlike findings with younger infants (at 4-6 months), slightly older infants in Experiment 1 displayed a robust preference for vowels with infant formants over adult formants when f0 was matched. The strength of this preference was also positively correlated with age among infants between 4 and 8 months. In Experiment 2, this preference favoring infant over adult formants was maintained when f0 values were modulated.
Conclusions: Infants between 6 and 8 months of age displayed a robust and distinct preference for speech with resonances specifying a vocal tract that is similar in size and length to their own. This finding, together with data indicating that this preference is not present in younger infants and appears to increase with age, suggests that nascent knowledge of the motor schema of the vocal tract may play a role in shaping this perceptual bias, lending support to current models of speech development.
Supplemental material: https://doi.org/10.23641/asha.17131805.