“Mummy, keep it steady”: phonetic variation shapes word learning at 15 and 17 months

Abstract

Fifteen-month-olds have difficulty detecting differences between novel words differing in a single vowel. Previous work showed that Australian English (AusE) infants habituated to the word-object pair DEET detected an auditory switch to DIT and DOOT in Canadian English (CanE) but not in their native AusE (Escudero et al., ). The authors speculated that this may be because the vowel inherent spectral change variation (VISC) in AusE DEET is larger than in CanE DEET. We investigated whether VISC leads to difficulty in encoding phonetic detail during early word learning, and whether this difficulty dissipates with age. In Experiment 1, we familiarized AusE-learning 15-month-olds to AusE DIT, which contains smaller VISC than AusE DEET. Unlike infants familiarized with AusE DEET (Escudero et al., ), infants detected a switch to DEET and DOOT. In Experiment 2, we familiarized AusE-learning 17-month-olds to AusE DEET. This time, infants detected a switch to DOOT, and marginally detected a switch to DIT. Our acoustic analysis showed that AusE DEET and DOOT are differentiated by the second vowel formant, while DEET and DIT can only be distinguished by their changing dynamic properties throughout the vowel trajectory. Thus, by 17 months, AusE infants can encode highly dynamic acoustic properties, enabling them to learn the novel vowel minimal pairs that are difficult at 15 months. These findings suggest that the development of word learning is shaped by the phonetic properties of the specific word minimal pair.

Cross‐Situational Learning of Phonologically Overlapping Words Across Degrees of Ambiguity

“… These vowels are also differentiated by their dynamic properties in AusE (Elvin, Williams, & Escudero, ; Escudero, Mulak, Elvin, & Traynor, ; Williams, Escudero, & Gafos, ). …”

Perceptual Sensitivity to Spectral Change in Australian English Close Front Vowels: An Electroencephalographic Investigation

“…For instance, the F1 × F2 trajectory of AusE /iː/ begins more central and moves towards the periphery of the F1 × F2 vowel space, whereas the F1 × F2 trajectories of /ɪ/ and /ɪə/ begin more peripheral and move towards the center (Figure 1). If spectral differences between the onsets and offsets of individual vowels are assumed to be important within the NRV framework, then the bias towards peripheral vowels would mean closing vowels are perceptually more prominent than centering vowels, explaining some of the present results (for further discussion, see [27] and [28]).…”

Infants use phonetic detail in speech perception and word learning when detail is easy to perceive

“…The authors used acoustic analyses of the stimuli to predict that infants would be most successful at discriminating the vowel contrasts Phonetic detail in infant speech perception and word learning 8 with the largest acoustic distance, regardless of whether they were produced in their native English variety. 1 Additionally, Australian 17-month-olds succeed at discriminating both Australian English /diːt/-/duːt/ and /diːt/-/dɪt/ in the Switch task, although learning was more robust for the former contrast (Escudero, Mulak, Elvin, & Traynor, 2018). The authors reported detailed acoustic analyses that showed that the vowels in the words /diːt/, /dɪt/, and /duːt/ differed significantly in their dynamic properties.…”

“…We hypothesised that if the acoustic properties of specific vowel contrasts do not influence phoneme discrimination during the second year of life, vowel discrimination for /diːt/-/duːt/ and /diːt/-/dɪt/ should be equally successful. Alternatively, the acoustic properties of the vowels may impact phoneme discrimination, in that the phonetic variation in the production of /diːt/, which reduces the phonetic distance between /diːt/ and /dɪt/, may make this contrast more difficult than /diːt/-/duːt/ (Escudero et al, 2018).…”

“…We hypothesised that if cognitive demands of the word-learning task determine infants' performance for both vowel and consonant minimal pairs (Yoshida et al, 2009), 15-month-old infants should demonstrate the ability to correctly map /diːt/ and /duːt/ to their respective referents. Alternatively, it may be that even a task with lower cognitive demands yields difficulty, which would suggest that further support from contextual cues (Waxman & Fennell 2010) may be needed for a contrast that only differs in a single acoustic dimension, namely F2 (Escudero et al, 2018).…”