Abstract
Infant directed speech (IDS), the speech register adults use when talking to infants, has been shown to have positive effects on attracting infants’ attention, language learning, and emotional communication. Here event related potentials (ERPs) are used to investigate the neural coding of IDS and ADS (adult directed speech) as well as their discrimination by both infants and adults. Two instances of the vowel /i/, one extracted from ADS and one from IDS, were presented to 9-month-old infants and adults in two oddball conditions: ADS standard/IDS deviant and IDS standard/ADS deviant. In Experiment 1 with adults, the obligatory ERPs that code acoustic information were different for ADS and IDS; and discrimination, indexed by mismatch negativity (MMN) responses, showed that IDS and ADS deviants were discriminated equally well; although, the P3a response was larger for IDS suggesting it captured adults’ attention more than did ADS. In infants the obligatory responses did not differ for IDS and ADS, but for discrimination, while IDS deviants generated both a slow-positive mismatch response (MMR) as well as an adult-like MMN, the ADS deviants generated only an MMR. The presence of a mature adult-like MMN suggests that the IDS stimulus is easier to discriminate for infants.
Highlights
Vowel hyperarticulation, a speaker’s tendency to exaggerate the articulation of vowels in their speech[9], has been proposed to serve a didactic function in Infant directed speech (IDS)
The first aim was to assess the differences in event related potentials (ERPs) to sound onset (N1-P2 response in adults) between IDS and ADS
The N1-P2 response is thought to reflect the processing of many of the spectral and temporal cues contained in speech that are critical for speech perception
Summary
A speaker’s tendency to exaggerate the articulation of vowels in their speech[9], has been proposed to serve a didactic function in IDS. Kuhl et al.[5] compared IDS and ADS vowel triangles produced by mothers speaking English, Russian, and Swedish, and found vowel hyperarticulation in all three language groups This has been shown to have linguistic benefits; mothers whose IDS shows greater vowel hyperarticulation have infants who show higher performance in speech discrimination tasks[10] and lexical processing[11]. The qualities of IDS appear to be shaped by reciprocal interaction between infants and their adult interlocutors In accord with such a notion, robust behavioural evidence indicates that infants both discriminate IDS from ADS and show an early preference for IDS20–23. Santesso et al.[26] reported increased electroencephalogram (EEG) power at frontal sites when 9-month-old infants listened to IDS compared with ADS This increased neural activity in the frontal regions in response to speech can lead to higher attention and more successful encoding of the incoming speech stream, which are highly beneficial for language learning. These peaks in the auditory ERPs are often called “obligatory responses” as they are generated by almost all audible sounds
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