Acoustic phenotypes for speech-genetics studies: an acoustic marker for residual /3`/ distortions

A companion paper addresses the need for phenotype markers for speech-genetics studies and provides reference data for US English rhotics that can be used for phenotype research. The present paper uses these reference data to derive and test an acoustic marker to discriminate the residual / / distortions of adolescents with two speech disorder histories. One speech disorder history includes signi® cant speech delay; the other history is a speech disorder limited to only speech sound distortions of /r/, / / and/or /2/. The ® rst subtype of speech delay is posited to be genetically transmitted, whereas the origins of the second subtype are posited to be associated with shared and non-shared environmental variance. Speech samples from 84 9 to 17-year-old speakers were divided into four groups based on speech history and speech errors at assessment. Group 1 children had prior speech delay and residual rhotic distortions, Group 2 children had only prior and residual rhotic distortions, and children in the two control groups had normal or normalized speech. Statistically signi® cant logistic regression models indicated that an acoustic marker successfully discriminated residual derhotacized / / tokens produced by speakers in Group 1 from residual derhotacized / / tokens produced by speakers in Group 2. The marker was a z score less than 6.0 for Formant 2 subtracted from Formant 3 (i.e. zF3 Õ F2<6.0) as measured at the constriction interval for / / targets. Sensitivity (percentage of correctly identi® ed derhotacized /Æ/ tokens from Group 1 speakers) for the acoustic marker was 85%. Speci® city (percentage of correctly rejected derhotacized /Æ/ tokens from Group 2 speakers) was 79%. Discussion considers methodological, phonological, and genetic perspectives that might account for the articulatory diŒerences in the residual / / distortions of adolescents with the two diŒerent speech histories.