Quantifying sources of variability in infancy research using the infant-directed-speech preference

Psychological scientists have become increasingly concerned with issues related to methodology and replicability, and infancy researchers in particular face specific challenges related to replicability: For example, high-powered studies are difficult to conduct, testing conditions vary across labs, and different labs have access to different infant populations. Addressing these concerns, we report on a large-scale, multisite study aimed at (a) assessing the overall replicability of a single theoretically important phenomenon and (b) examining methodological, cultural, and developmental moderators. We focus on infants’ preference for infant-directed speech (IDS) over adult-directed speech (ADS). Stimuli of mothers speaking to their infants and to an adult in North American English were created using seminaturalistic laboratory-based audio recordings. Infants’ relative preference for IDS and ADS was assessed across 67 laboratories in North America, Europe, Australia, and Asia using the three common methods for measuring infants’ discrimination (head-turn preference, central fixation, and eye tracking). The overall meta-analytic effect size (Cohen’s d) was 0.35, 95% confidence interval = [0.29, 0.42], which was reliably above zero but smaller than the meta-analytic mean computed from previous literature (0.67). The IDS preference was significantly stronger in older children, in those children for whom the stimuli matched their native language and dialect, and in data from labs using the head-turn preference procedure. Together, these findings replicate the IDS preference but suggest that its magnitude is modulated by development, native-language experience, and testing procedure. (This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 798658.

Speech discrimination in infants at family risk of dyslexia: Group and individual-based analyses

Deficiencies in discriminating and identifying speech sounds have been widely attested in individuals with dyslexia as well as in young children at family risk (FR) of dyslexia. A speech perception deficit has been hypothesized to be causally related to reading and spelling difficulties. So far, however, early speech perception of FR infants has not been assessed at different ages within a single experimental design. Furthermore, a combination of group- and individual-based analyses has not been made. In this cross-sectional study, vowel discrimination of 6-, 8-, and 10-month-old Dutch FR infants and their nonrisk (no-FR) peers was assessed. Infants (N = 196) were tested on a native English /aː/–/eː/ and non-native English /ɛ/–/æ/ contrast using a hybrid visual habituation paradigm. Frequentist analyses were used to interpret group differences. Bayesian hierarchical modeling was used to classify individuals as speech sound discriminators. FR and no-FR infants discriminated the native contrast at all ages. However, individual classification of the no-FR infants suggests improved discrimination with age, but not for the FR infants. No-FR infants discriminated the non-native contrast at 6 and 10 months, but not at 8 months. FR infants did not show evidence of discriminating the contrast at any of the ages, with 0% being classified as discriminators. The group- and individual-based data are complementary and together point toward speech perception differences between the groups. The findings also indicate that conducting individual analyses on hybrid visual habituation outcomes is possible. These outcomes form a fruitful avenue for gaining more understanding of development, group differences, and prospective relationships

A step forward: Bayesian hierarchical modelling as a tool in assessment of individual discrimination performance

Individual assessment of infants’ speech discrimination is of great value for studies of language development that seek to relate early and later skills, as well as for clinical work. The present study explored the applicability of the hybrid visual fixation paradigm (Houston et al., 2007) and the associated statistical analysis approach to assess individual discrimination of a native vowel contrast, /aː/ - /eː/, in Dutch 6 to 10-month-old infants. Houston et al. found that 80% (8/10) of the 9-month-old infants successfully discriminated the contrast between pseudowords boodup - seepug. Using the same approach, we found that 12% (14/117) of the infants in our sample discriminated the highly salient /aː/ -/eː/ contrast. This percentage was reduced to 3% (3/117) when we corrected for multiple testing. Bayesian hierarchical modeling indicated that 50% of the infants showed evidence of discrimination. Advantages of Bayesian hierarchical modeling are that 1) there is no need for a correction for multiple testing and 2) better estimates at the individual level are obtained. Thus, individual speech discrimination can be more accurately assessed using state of the art statistical approaches

Contrasting behavioral looking procedures: a case study on infant speech segmentation

This paper compared three different procedures common in infant speech perception research: a headturn preference procedure (HPP) and a central-fixation (CF) procedure with either automated eye-tracking (CF-ET) or manual coding (CF-M). In theory, such procedures all measure the same underlying speech perception and learning mechanisms and the choice between them should ideally be irrelevant in unveiling infant preference. However, the ManyBabies study (ManyBabies Consortium, 2019), a cross-laboratory collaboration on infants' preference for child-directed speech, revealed that choice of procedure can modulate effect sizes. Here we examined whether procedure also modulates preference in paradigms that add a learning phase prior to test: a speech segmentation paradigm. Such paradigms are particularly important for studying the learning mechanisms infants can employ for language acquisition. We carried out the same familiarization-then-test experiment with the three different procedures (32 unique infants per procedure). Procedures were compared on various factors, such as overall effect, average looking time and drop-out rate. The key observations are that the HPP yielded a larger familiarity preference, but also reported larger drop-out rates. This raises questions about the generalizability of results. We argue that more collaborative research into different procedures in infant preference experiments is required in order to interpret the variation in infant preferences more accurately

A step forward: Bayesian hierarchical modelling as a tool in assessment of individual discrimination performance

Individual assessment of infants’ speech discrimination is of great value for studies of language development that seek to relate early and later skills, as well as for clinical work. The present study explored the applicability of the hybrid visual fixation paradigm (Houston et al., 2007) and the associated statistical analysis approach to assess individual discrimination of a native vowel contrast, /aː/ - /eː/, in Dutch 6 to 10-month-old infants. Houston et al. found that 80% (8/10) of the 9-month-old infants successfully discriminated the contrast between pseudowords boodup - seepug. Using the same approach, we found that 12% (14/117) of the infants in our sample discriminated the highly salient /aː/ -/eː/ contrast. This percentage was reduced to 3% (3/117) when we corrected for multiple testing. Bayesian hierarchical modeling indicated that 50% of the infants showed evidence of discrimination. Advantages of Bayesian hierarchical modeling are that 1) there is no need for a correction for multiple testing and 2) better estimates at the individual level are obtained. Thus, individual speech discrimination can be more accurately assessed using state of the art statistical approaches

Speech discrimination in infants at family risk of dyslexia: Group and individual-based analyses

Deficiencies in discriminating and identifying speech sounds have been widely attested in individuals with dyslexia as well as in young children at family risk (FR) of dyslexia. A speech perception deficit has been hypothesized to be causally related to reading and spelling difficulties. So far, however, early speech perception of FR infants has not been assessed at different ages within a single experimental design. Furthermore, a combination of group- and individual-based analyses has not been made. In this cross-sectional study, vowel discrimination of 6-, 8-, and 10-month-old Dutch FR infants and their nonrisk (no-FR) peers was assessed. Infants (N = 196) were tested on a native English /aː/–/eː/ and non-native English /ɛ/–/æ/ contrast using a hybrid visual habituation paradigm. Frequentist analyses were used to interpret group differences. Bayesian hierarchical modeling was used to classify individuals as speech sound discriminators. FR and no-FR infants discriminated the native contrast at all ages. However, individual classification of the no-FR infants suggests improved discrimination with age, but not for the FR infants. No-FR infants discriminated the non-native contrast at 6 and 10 months, but not at 8 months. FR infants did not show evidence of discriminating the contrast at any of the ages, with 0% being classified as discriminators. The group- and individual-based data are complementary and together point toward speech perception differences between the groups. The findings also indicate that conducting individual analyses on hybrid visual habituation outcomes is possible. These outcomes form a fruitful avenue for gaining more understanding of development, group differences, and prospective relationships

Contrasting behavioral looking procedures: a case study on infant speech segmentation

This paper compared three different procedures common in infant speech perception research: a headturn preference procedure (HPP) and a central-fixation (CF) procedure with either automated eye-tracking (CF-ET) or manual coding (CF-M). In theory, such procedures all measure the same underlying speech perception and learning mechanisms and the choice between them should ideally be irrelevant in unveiling infant preference. However, the ManyBabies study (ManyBabies Consortium, 2019), a cross-laboratory collaboration on infants' preference for child-directed speech, revealed that choice of procedure can modulate effect sizes. Here we examined whether procedure also modulates preference in paradigms that add a learning phase prior to test: a speech segmentation paradigm. Such paradigms are particularly important for studying the learning mechanisms infants can employ for language acquisition. We carried out the same familiarization-then-test experiment with the three different procedures (32 unique infants per procedure). Procedures were compared on various factors, such as overall effect, average looking time and drop-out rate. The key observations are that the HPP yielded a larger familiarity preference, but also reported larger drop-out rates. This raises questions about the generalizability of results. We argue that more collaborative research into different procedures in infant preference experiments is required in order to interpret the variation in infant preferences more accurately