Acoustics of –<i>s</i> Morphemes (Ebert et al., 2025)

<p dir="ltr"><b>Purpose: </b>Seemingly homophonous English –<i>s</i> suffixes may have distinct phonetic realizations. Reports diverge on how plural, possessive, and third singular –<i>s</i> morphemic conditions differ from nonmorphemic fricatives in acoustic noise duration and fricative center of gravity (CoG). This lack of consensus can be explained by varying methodological decisions. The present study sought to resolve the open question of how duration and CoG vary for each –<i>s</i> allomorph depending on sentence position, morpheme type, and phoneme category (i.e., [s, z]).</p><p dir="ltr"><b>Method: </b>Nine participants read 80 allomorphs in experimental sentence stimuli that controlled coda complexity, word and sentence stress, verb transitivity, sentence length, and surrounding phonemes.</p><p dir="ltr"><b>Results:</b> A linear mixed model for duration revealed significant interactions between sentence position, morpheme type, and phoneme category for duration. Further pairwise comparisons revealed the expected effects of sentence position and that plural and third person singular [z] were significantly shorter than nonmorphemic [z] in the medial position. The model for CoG detected an effect of sentence position with lower frequencies in the sentence final position, although there were no differences across morphemic and nonmorphemic uses.</p><p dir="ltr"><b>Conclusions: </b>Results best aligned with studies that were similarly inclusive of a full suite of sentence positions, morphemes, and phonemes. This study refined previous methodology with a controlled experimental design using reading stimuli rather than conversation, lending applications for morphosyntax intervention and theoretical implications for speech science and developmental psycholinguistics. The control over the phonetic environment in the stimuli can inform future investigations of –<i>s</i> allomorph perception.</p><p dir="ltr"><b>Supplemental Material S1.</b> Fixed effects estimates for the duration model as a function of Sentence Position (medial vs. final), Morpheme Type (non-morphemic, plural, possessive, third person singular), and Phoneme Category ([s] vs. [z]). The dropped levels were [z] (Phoneme Category), third person singular (Morpheme Type), and final position (Sentence Position). All predictors were sum-coded. Estimates reflect deviations from the grand mean. Standard errors and t-values are reported.</p><p dir="ltr"><b>Supplemental Material S2.</b> Fixed effects estimates for the center of gravity model as a function of Sentence Position (medial vs. final), Morpheme Type (non-morphemic, plural, possessive, third person singular), and Phoneme Category ([s] vs. [z]). The dropped levels were [z] (Phoneme Category), third person singular (Morpheme Type), and final position (Sentence Position). All predictors were sum-coded. Estimates reflect deviations from the grand mean. Standard errors and t-values are reported.</p><p dir="ltr">Ebert, R., Fitzgerald, C. E., & Whitfield, J. A. (2025). Acoustic properties of –<i>s</i> related morphemes in English: A methodological reevaluation. <i>Journal of Speech, Language, and Hearing Research. </i>Advance online publication. <a href="https://doi.org/10.1044/2025_JSLHR-24-00629" rel="noreferrer" target="_blank">https://doi.org/10.1044/2025_JSLHR-24-00629</a></p>