Consonant Neutralization and Vowel Space Area in Tashlhiyt Berber’s Infant-Directed Speech

Infant-Directed Speech (IDS) and Adult-Directed Speech (ADS) are two registers that can differ across multiple linguistic domains and social contexts. In languages where the phonemes’ acoustic clarity is modified, there is a typical assumption in the literature that these phonemes are either hyper - or hypo -articulated. These modifications have received considerable attention in language research, serving as the basis of proposals concerning the potential didactic and communicative (e.g., affective) functions of IDS. The current study adds to this literature by examining how vowels and consonants are modified in IDS in a previously unstudied African language with an unusual phoneme inventory: Tashlhiyt Berber. Seven caregivers were recorded interacting with: (a) infants between the ages of 0;6 and 1;5, and (b) an adult experimenter who is a native speaker of Tashlhiyt. In IDS, we found longer vowel duration for content words and exaggerated pitch levels across the board, successfully replicating cross-linguistic patterns. Counter to the hyper-articulation hypothesis, there was more vowel overlap in IDS, while no differences were observed between IDS and ADS for overall vowel space size. We additionally found that speakers tend to completely neutralize certain consonant contrasts in IDS, rendering them indistinguishable to the infant. Our results are most consistent with the proposal that caregivers use IDS to guide and maintain their infant’s attention and to convey positive affect.