Asymmetric headturning to speech and nonspeech in human newborns.

Abstract

Functional asymmetries were examined in 59 newborns by recording headturns from midline to binaurally equivalent sounds. Results showed that robust, asymmetric pattern of headturning occurred in most newborns' responses to binaurally presented unfiltered female speech sounds, with increased rightward orientation demonstrated in five replications. Female speech that was modified by attenuation of frequencies above 500 Hz, as well as speech attenuated below 1500 Hz and above 3000 Hz, resulted in a significant rightward bias in headturning. In contrast, female speech attenuated below 3500 Hz, and continuous, repetitive stimuli such as heartbeat sounds and phrases of speech repeated at the rate of heartbeat (termed heartspeech), failed to generate the rightward orientation bias. These results suggest that female speech sounds, particularly low-frequency sounds related to the naturally occurring prosodic characteristics of speech, are a salient class of stimuli for the organization of lateral biases in orienting in newborns.