Published online 03 February 2021The functions of acoustic-phonetic modifications in infant-directed speech (IDS) remain a
question: do they specifically serve to facilitate language learning via enhanced phonemic
contrasts (the hyperarticulation hypothesis) or primarily to improve communication via
prosodic exaggeration (the prosodic hypothesis)? The study of lexical tones provides a
unique opportunity to shed light on this, as lexical tones are phonemically contrastive,
yet their primary cue, pitch, is also a prosodic cue. This study investigated Cantonese
IDS and found increased intra-talker variation of lexical tones, which more likely posed
a challenge to rather than facilitated phonetic learning. Although tonal space was
expanded which could facilitate phonetic learning, its expansion was a function of
overall intonational modifications. Similar findings were observed in speech to pets
who should not benefit from larger phonemic distinction. We conclude that lexicaltone
adjustments in IDS mainly serve to broadly enhance communication rather than
specifically increase phonemic contrast for learners.This work was supported by the University Grants Committee (HKSAR) (RGC34000118), the Innovation and
Technology Fund (HKSAR) (ITS/067/18), Dr. Stanley Ho Medical Development Foundation, and the
Global Parent Child Resource Centre Limited. The second author’s work is supported by the Basque
Government through the BERC 2018-2021 program and by the Spanish Ministry of Science and
Innovation through the Ramon y Cajal Research Fellowship, PID2019-105528GA-I00
