Frequency and context prominence effects on English allophone perception: Identification of /r/ and /<b> <i>θ</i> </b>/

Purpose: External evidence from multiple cross-linguistics studies suggests the importance of acoustic clarity of speech sounds in words can vary for decoding speech (Gurevich &amp; Kim, 2023b). Dependence on acoustic salience is modulated by the structure and function of words (Bell et al., 2003; Jun, 2011; Jurafsky et al., 2001; Scharenborg et al., 2016). This perception study of English examines the functional importance of positional allophones to intelligibility. Methods: Speech produced by 21 speakers reading five randomized lists of 308 words with high coverage of English allophones (from Gurevich &amp; Kim, 2023a) was presented to 11 naïve listeners for identification using a Latin-square design. The identification accuracy of the highest and the lowest frequency sounds were compared in their most and least prominent positions. Results: A total of 257 perceptual judgements were analyzed. Word-initial prevocalic /r/ and /θ/ had 97% and 75% accuracies, respectively; the pre-consonantal /r/ and inter-consonantal /θ/ had 95% and 43% accuracies, respectively. Conclusions: The results experimentally corroborate the expected hierarchy where higher frequency allophones in prominent contexts show higher accuracy compared to lower frequency allophones in less prominent contexts. Investigating allophones in additional languages will explore the effect of phonology on perception.