Phrases, prelinguistic vocalizations, and hearing impairment
Abstract
The primary aims of the present investigation were to replicate and extend previous findings regarding phrasing in the vocalizations of typically developing infants and to evaluate the role of audition and vocal maturity in the formation of phrasing. A subsidiary purpose was to determine whether differences existed in volubility of vocalizations across hearing status and across level of vocal maturity. Eight infants with normal hearing (NH) and eight infants with severe-to-profound and profound hearing impairment (HI) were studied at three levels of vocal development: precanonical, canonical, and postcanonical. Adult intuitive judgments were used to identify rhythmic groupings in infants' prelinguistic vocalizations. Similar to findings from previous investigations, listeners reliably identified a hierarchy of rhythmic groupings in infants' vocalizations such that syllables were grouped into utterances, and approximately three-fourths of all utterances were grouped into phrases. Other utterances were isolated, i.e., they were not grouped into phrases. Acoustic examination confirmed some previous findings regarding the internal organization of prelinguistic phrases, e.g., duration of utterances was more similar to following silences when utterances were embedded in phrases than when utterances were isolated. Other findings, e.g., final syllable lengthening (FSL) is characteristic of phrase endings, were not confirmed. All utterances in phrases were characterized by systematic FSL. In addition, duration of utterances in phrases and duration of silences between these utterances was greater than that obtained previously. These discrepant findings suggest that a more in depth examination of the perceptual basis of phrasing should be conducted. Significant differences in the temporal features of rhythmic units, e.g., absolute duration, across infants with NH and HI were observed. This result implied that audition can influence the adequate development of rhythmic units. Organization of higher-order rhythmic units also varied according to level of vocal development. Duration of isolated utterances increased with vocal development whereas duration of phrases decreased with vocal development. Volubility of vocalizations, i.e., units per minute, was found to be robust to differences in vocal maturity and loss of audition suggesting that quantitative aspects of prelinguistic vocalizations are stable features.
Degree
Ph.D.
Advisors
Leonard, Purdue University.
Subject Area
Speech therapy|Audiology|Cellular biology
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