Does harmonicity explain children's cue weighting of fricative-vowel syllables?

When labeling syllable-initial fricatives, children have been found to weight formant transitions more and fricative-noise spectra less than adults, prompting the suggestion that children attend more to the slow vocal-tract movements that create syllabic structure than to the rapid gestures more closely aligned with individual phonetic segments. That explanation fits well with linguistic theories, but an alternative explanation emerges from auditory science: Perhaps children attend to formant transitions because they are found in voiced signal portions, and so formants share a common harmonic structure. This work tested that hypothesis by using two kinds of stimuli lacking harmonicity: sine-wave and whispered speech. Adults and children under 7 years of age were asked to label fricative-vowel syllables in each of those conditions, as well as natural speech. Results showed that children did not change their weighting strategies from those used with natural speech when listening to sine-wave stimuli, but weighted formant transitions less when listening to whispered stimuli. These findings showed that it is not the harmonicity principle that explains children's preference for formant transitions in phonetic decisions. It is further suggested that children are unable to recover formant structure when those formants are not spectrally prominent and/or are noisy.