PONE-D-24-37730Pitch characteristics of real-world infant-directed speech vary with pragmatic context, perceived adult gender, and infant genderPLOS ONE

Dear Dr. Neer,

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Reviewers' comments:

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1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Partly

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available?

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Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

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Reviewer #2: Yes

Reviewer #3: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The manuscript investigates how prosodic modifications in infant-directed speech (IDS) vary based on pragmatic context, perceived adult gender, and infant gender. Analyzing 3,607 speech clips from daylong home recordings of 60 North American infants, the study assesses pitch characteristics across various speaking contexts. The authors exhibit rigor and transparency in their study design, including preregistration of their analyses. They clearly detail the method for assigning adult gender, which is noted as a study limitation—a commendable inclusion. I appreciate the authors’ distinction between planned and exploratory analyses, enhancing the clarity of the reporting. Below, I list some minor suggestions for revision:

1. The authors also provide a detailed explanation of inter-coder reliability, noting the average across four rounds of coding. Given that the practice of averaging reliability has been debated, it would be helpful if the authors also reported the range to give a fuller picture. For example, the reliability for most categories is strong, though it is lower for "Conversational Basics" (0.55). Further explanation on why this category’s reliability is comparatively low and how this may affect the interpretation of results would be valuable.

2. There are a few areas that require further clarification. For instance, it is not entirely clear if "3,727 adult speech audio clips" refers to distinct utterances. Later, the authors mention “3,607 adult speaker utterances (2,210 IDS; 1,397 ADS) after exclusions,” suggesting that all clips were treated as individual utterances. How were utterances determined? In the OSF repository, the first clip (comfort_inform_CDS) includes two grammatical segments (clauses). Were they counted as one utterance?

3. The pragmatic context coding scheme for utterances includes categories such as "Inform," "Conversational Basics," "Question," "Imperative," "Reading," "Singing," "Comfort," and "Vocal Play." It would be helpful to know whether all utterances fit into these categories or if there were cases that could not be coded within this framework.

4. Beyond the factors analyzed, I am curious if the authors considered other potential influences. For example, was the time of day when utterances occurred recorded, and could this factor influence speaker presence by gender? Additionally, given that 43 infants had parents with higher education, could parental education also play a role in prosodic modification patterns?

5. Further detail on the perceived gender distribution of adult speakers within each participant and across the total sample is recommended. Providing descriptive information about these characteristics would offer a clearer picture of the sample's demographic composition. It would also be beneficial if the authors elaborated on the automatic pitch detection methodology and whether they validated this method against human-coded data.

Overall, the manuscript offers a valuable contribution to the field, with results well-placed within the broader child development literature. While the core findings are robust and data-supported, further refinement in presentation and organization would enhance the manuscript’s clarity and impact.

Reviewer #2: First of all, I would like to congratulate the authors on this interesting study. The topic is relevant, the conducted experiment is feasible and the applied statistical analyses are well described, clear and appropriate. The authors discussed all important aspects, including the limitations of the study. I definitely recommend this manuscript for publication. I only have some minor comments and suggestions.

1. I am not familiar of LENA device and its working mechanism. On the official website I read that it’s deleting the actual conversation and store only the acoustic data in order to meet personality rights. If so, how audio playbacks were coded by the coders? The website also stated that the device is not able to “understand” spoken words but it can count the words. But it can also count utterances (as in the article there are information about the number of utterances). In the article there are also utterance-level acoustic characteristics, so it seems that the device is able to do utterance-level analyses. Is it able to do hyperarticulation analyses? Or any other vowel-level analyses? Anyway, it would be expedient to write a little bit more about the device, the software, the output, etc. for those who are not familiar with this data acquisition method.

2. It would be also nice to have a table with the number of clips in each pragmatic context category (authors noted that Reading and Vocal play were underrepresented and sometimes these contexts were excluded from analysis, but it would be important to see the exact numbers within each pragmatic context). It would be also important to see the exclusion rate of clips within each pragmatic context. For instance, we can read in the discussion that authors were surprised that comfort was rare in the dataset. But isn’t it possible that most of the comfort context had been excluded because the infant was crying and as it was considered as “noisy”? A detailed table about excluded clips would give an answer to this question.

3. Line 252 criterion of at least 20 utterances seems a little bit arbitrary. What was the basis for this inclusion criteria?

Reviewer #3: The study "Pitch characteristics of real-world infant-directed speech vary with pragmatic context, perceived adult gender, and infant gender" explores how various factors influence the acoustic properties of infant-directed speech (IDS). Using an open dataset of speech clips recorded in the naturalistic environments of North American homes with infants aged 3 to 20 months, the authors compared the pitch features of IDS with adult-directed speech (ADS). Their analysis confirmed that IDS consistently exhibits a higher mean pitch and greater pitch variability compared to ADS, aligning with previous findings. Moreover, the study revealed that these pitch characteristics are not uniform but vary depending on the pragmatic function of the utterance, the gender of the speaker, and the gender of the infant. These findings highlight the nuanced and context-sensitive nature of IDS, underscoring its potential role in facilitating infant engagement and learning.

The authors made commendable efforts to address the issue of zero counts in some pragmatic contexts by introducing a randomization-based approach to include these categories in their logistic mixed-effects model. However, the limited observations for contexts such as 'reading,' 'singing,' and 'comforting,' particularly in the ADS register, raise concerns about the robustness of the conclusions drawn for these categories. Sparse or absent data for certain pragmatic contexts inherently limit the statistical power and reliability of the model's estimates for these categories. The artificial reclassification of data to enable model convergence, while creative, introduces additional uncertainty and potential biases that complicate the interpretability of the findings for these specific contexts.

The results from running the logistic mixed-effects model provided in the manuscript's accompanying code revealed no significant main effect of the pragmatic context of questions on the register, contrary to the findings reported in the paper (see attached html table). This discrepancy reinforces concerns about the robustness of the analysis, particularly given the limited observations for some pragmatic contexts and the reliance on resampling techniques to address zero counts. Furthermore, the warning message generated during model execution—“Model is nearly unidentifiable: large eigenvalue ratio - Rescale variables?”—raises additional doubts about the model's stability and reliability.

The study analyzes IDS across a broad age range of 3 to 20 months, which spans a critical period of infant development. Previous research has demonstrated that IDS evolves as infants grow, with notable changes in pitch characteristics (e.g., Cox et al., 2023), and pragmatic functions tailored to developmental stages, such as capturing young infants’ attention and conveying emotional affect versus supporting linguistic goals in older infants (Fernald, 1992; Kuhl et al., 1997). By aggregating data across this wide age range without accounting for potential developmental differences, the study may obscure important age-specific patterns in IDS. For example, pitch characteristics or the frequency of certain pragmatic contexts (e.g., comforting vs. reading) may differ markedly between younger and older infants, which could confound the results. A more nuanced analysis that examines IDS characteristics by narrower age bands or includes age as a covariate could provide deeper insights into how pragmatic contexts and pitch modulations vary across development.

Furthermore, the inclusion of Spanish utterances in the dataset introduces an additional variable that could influence the pitch characteristics of IDS, as cross-linguistic research has shown that IDS varies significantly across languages (e.g., Fernald et al., 1989). For instance, Spanish IDS may exhibit different pitch ranges, prosodic contours, or modulation patterns compared to English IDS due to phonological and cultural differences in speech patterns (e.g., Cox et al., 2023). These linguistic variations could confound the analysis, particularly if the distribution of Spanish and English utterances is uneven across pragmatic contexts, speaker genders, or infant age groups.

Differences in the pitch characteristics of male and female speakers in the context of singing could be influenced by the type of songs they sing rather than solely reflecting their vocal pitch range or communication style. This is a critical point to consider, as song selection can vary systematically by gender due to cultural, social, or individual preferences, which may introduce confounding factors into the analysis. It is unclear whether the observed pitch differences in singing across genders reflect biological differences in vocal range, variations in song choice, or a combination of these factors.

One of the notable strengths of this study is its commitment to transparency and reproducibility, exemplified by the accessibility of both the data and analysis code. By utilizing an existing open dataset of speech recordings, the authors enable other researchers to verify their findings and extend the work in new directions. Moreover, the availability of the analysis code provides a clear roadmap for reproducing the statistical models and simulations, facilitating peer verification.

Overall, this study offers valuable insights into how pitch characteristics of IDS vary by pragmatic context, speaker gender, and infant gender, yet several limitations and potential confounds warrant careful consideration. The broad age range of 3 to 20 months introduces variability that may obscure developmental changes in IDS, as prior research has shown that IDS evolves with infants’ linguistic and social development. Additionally, the sparse or absent observations for certain pragmatic contexts, such as reading and vocal play, especially in ADS, raise questions about the robustness of the conclusions drawn from these data. The method of artificially reclassifying utterances to address zero counts, while creative, introduces uncertainty and potential bias. Lastly, the observed gender differences in the context of singing could reflect differences in song selection rather than purely biological vocal characteristics or interaction styles. Addressing these issues through more stratified age analyses, and controls for song content—would strengthen the study’s claims and contribute to a more nuanced understanding of IDS dynamics.

Minor points:

Line 115: can LENA capture 16 hours a day? Limited by battery capacity or by storage capacity?

Line 144: But how is it measured automatically?

Line 200 ff: It seems not clear to me, whether a speech clip is synonymously used for utterance and what is meant by a conversational block (especially with regard to identifying how many utterances were in Spanish).

Line 220: How were annotators bling to the child’s gender? Couldn’t this be similarly perceived as the adult speaker’s gender?

Line 330: It might be better to use identical labels within figure and manuscript – standard deviation of pitch versus pitch variability

End of tables and figures are hard to parse: Possibly add “Note” to text below tables and figures still belonging to them.

Supplemental Material Code (Alt analyses): line 122 the infant model mean is missing a + after the interaction of adu_gender*chi_gender*comfort

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Reviewer #1: No

Reviewer #2: Yes:  Dr. Anna Gergely

Reviewer #3: No

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PONE-D-24-37730R1Pitch characteristics of real-world infant-directed speech vary with pragmatic context, perceived adult gender, and infant genderPLOS ONE

Dear Dr. Neer,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by May 30 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

• A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
• A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
• An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols . Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols .

We look forward to receiving your revised manuscript.

Kind regards,

Marcela de Lourdes Peña Garay, Ph.D

Academic Editor

PLOS ONE

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Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #3: (No Response)

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #3: Partly

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #3: Yes

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4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #3: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #3: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: I appreciate the opportunity to review this revised manuscript. The authors have adequately addressed all of my previous comments.

Reviewer #3: I appreciate the thoughtful and thorough revisions made in response to the initial feedback. The authors have substantially improved the manuscript by increasing methodological transparency and adopting a Bayesian modeling approach to address issues related to sparse data. The updated analyses are clearly reported, and the convergence diagnostics suggest a well-specified model.

The authors note that adult speaker gender was removed from the Bayesian model to achieve convergence—an understandable decision given the data limitations and model complexity. However, since adult gender was central to the study’s original hypotheses and included in the preregistration, it would be helpful to explicitly acknowledge this as a deviation from the preregistered analysis and briefly reflect on its implications for interpreting the results. In addition, I recommend that the authors clearly state that the adoption of the Bayesian approach also constitutes a deviation from the preregistration (Variables and Analyses 1).

Reproducing the Bayesian analysis requires substantial computational time and resources (taking 11 hours for the Bayesian model to run on my end!). This could pose a barrier to reproducibility for researchers without access to high-performance computing setups. I suggest the authors consider caching model outputs (e.g., using saveRDS() or storing fitted model objects) and including them in the repository. This would facilitate transparency and reproducibility without requiring each user to rerun time-intensive sampling.

Minor:

p. 16: max_treedepth is 15 within the code but reported as 12 in the manuscript

Scaling and centering of binary predictors such as adult speaker gender, child gender, and register are performed using the scale() function. I am wondering whether effect coding (e.g., −0.5 / 0.5) would typically offer a more interpretable and robust approach in this context?

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Reviewer #1: No

Reviewer #3: No

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Pitch characteristics of real-world infant-directed speech vary with pragmatic context, perceived adult gender, and infant gender

PONE-D-24-37730R2

Dear Dr. Neer,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Marcela de Lourdes Peña Garay, Ph.D

Academic Editor

PLOS ONE

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