The study of speech naturalness in communication disorders: A systematic review of the literature.

The concept of speech naturalness is used widely in clinic and research applications. Unfortunately, the lack of consistency in research methods means that comparing findings between studies is difficult at best. In order to better understand the state of research on speech naturalness in communication disorders and quantify these impressions, this study looks at publications from the last 18 years in a systematic manner. A literature search for the exact phrase "speech naturalness" of the PubMed/MEDLINE, EBSCO, and ASHAWire databases was conducted. Articles included in the review were studies of communication and communication disorders published between 1990 and the end of 2014, in English, and in a peer-reviewed journal. 63 articles were selected and coded using a coding sheet adapted from a prior systematic review on intelligibility and cleft palate. Speech naturalness is an object of study in many subfields of communication disorders. Several concerns were raised as a result of the review, including the reliability and validity of measures, inadequate definitions of terminology, lack of detail in method descriptions, and the need to address relationships between naturalness and other variables included in the studies. Future studies should more carefully report methods and operational definitions used and more studies examining the relationship between naturalness and other speech variables in a variety of communication disorders are greatly needed.

Relationship between acoustic measures and speech naturalness ratings in Parkinson's disease: A within-speaker approach.

This study investigated the acoustic basis of across-utterance, within-speaker variation in speech naturalness for four speakers with dysarthria secondary to Parkinson's disease (PD). Speakers read sentences and produced spontaneous speech. Acoustic measures of fundamental frequency, phrase-final syllable lengthening, intensity and speech rate were obtained. A group of listeners judged speech naturalness using a nine-point Likert scale. Relationships between judgements of speech naturalness and acoustic measures were determined for individual speakers with PD. Relationships among acoustic measures also were quantified. Despite variability between speakers, measures of mean F0, intensity range, articulation rate, average syllable duration, duration of final syllables, vocalic nucleus length of final unstressed syllables and pitch accent of final syllables emerged as possible acoustic variables contributing to within-speaker variations in speech naturalness. Results suggest that acoustic measures correlate with speech naturalness, but in dysarthric speech they depend on the speaker due to the within-speaker variation in speech impairment.

An analysis of the sonority hypothesis and cluster realization in a child with phonological disorder.

This study describes the realization of onset and coda clusters in a 4-year old child acquiring American English, and with a higher than usual level of unintelligible speech. It reviews previous studies that have tested cluster realization against markedness and, in particular, the sonority hypothesis. This latter predicts steep rises in sonority at onsets and more gradual falls in sonority at codas of syllables. The data collected for this study cover four different onset cluster types and three different coda cluster types, and are derived from spontaneous speech produced during clinical sessions. An analysis of the patterns of cluster realizations shows that the participant's cluster realizations do not always follow the sonority hypothesis, and various factors are discussed that could be motivating the child's choice of realization.

The importance of narrow phonetic transcription for highly unintelligible speech: some examples.

The importance of the use of narrow phonetic transcription in transcribing a variety of speech disorders is emphasized. This point is illustrated with clinical data from the authors' own research. The examples used are the transcription of a severely disfluent client, a child with progressive hearing loss, repair sequences in dysarthric speakers, a child with idiosyncratic velar articulations, and an adult with progressive speech degeneration. The use of the extended International Phonetic Alphabet (IPA) for the transcription of disordered speech and the Voice Quality Symbols (VoQS) system for transcribing voice quality is introduced and illustrated in the examples provided. The need for training in narrow transcription is discussed as part of a combination of impressionistic and instrumental description techniques.