Infants’ Lexical Processing: Independent Contributions of Attentional and Clarity Cues

Abstract

There is a long-standing debate in the literature about the benefits thatacoustic components of Infant Directed Speech (IDS) might have for infants’language acquisition. One of the highly contested features is vowel spaceexpansion, which refers to the enlargement of the acoustic space betweenthe corner vowels /i, u, a/ in IDS compared to Adult Directed Speech (ADS).Some evidence indicates that vowel space expansion in IDS facilitatesinfants’ speech perception, thus promoting language development, whereasother studies have questioned these benefits and have proposed that anyprocessing benefits of IDS are due to its other prosodic features such asexaggerated and variable pitch. This study aimed to tease apart the effects ofvowel space expansion and prosodic exaggeration in IDS on 18-month-oldinfants’ speech processing. Using a looking-while-listening paradigm, twobetween-subjects conditions were compared: Exaggerated Pitch (with exag-gerated pitch height and range, but without vowel space expansion) andExpanded Vowel Space (with vowel space expansion, but no exaggeration inpitch height and range). Our results showed that infants recognized themeanings of the words more accurately in the Expanded Vowel Spacecompared to the Exaggerated Pitch condition. This suggests that vowelspace expansion in IDS facilitates infants’ lexical processing even when itdoes not cooccur with the prosodic exaggeration typical of IDS.