Melody of Vocants: Fixed Pattern or Shaped by Hearing?

Vocants as infants' first vocalic utterances are produced laryngeally while the vocal tract is maintained in a neutral position. These "primitive" sounds have sometimes been described as largely innate and, therefore, as sounding alike in both healthy and hearing-impaired young infants.

The objective of this study is to compare melody features of vocants, recorded during face-to-face interaction, between infants (N = 8) with profound congenital sensorineural hearing loss (HI group) and age-matched (N = 18) controls (CO) group. The question was as follows: does a lack of auditory feedback have a noticeable effect on melodic features of vocants?

The cooing database totalled 6,998 vocalizations (HI: N = 2,847; CO: N = 4,151), all of which had been recorded during the observation period of 60-181 days of age. Identification of the vocants (N = 1,148) was based on broadband spectrograms (KAY-CSL) and auditory impressions. Fundamental frequency (F0) analyses were performed (PRAAT) and the pattern of the F0 contour (melody) analysed using specific in-lab software (CDAP, pw-project). Generalized mixed linear models were used to perform group comparisons.

There was a clear predominance of a simple rising-falling pattern (single melody arcs) in vocants of both groups. Nonetheless, significantly more complex contours, particularly, double-arc structures, were found in vocants of the CO group. Moreover, vocants of the HI group were shorter than those uttered by the CO group, while the mean F0 did not significantly differ.

Vocants are characterized by both, innate features, found in HI and CO groups, and features that additionally require a functioning auditory system. Even at an early pre-linguistic stage, somatosensory sensations cannot compensate for a lack of auditory feedback. Vocants might be relevant in the early diagnosis of hearing disorders and assessments of the effectiveness of, or adjustments required to, hearing aids.