PONE-D-21-30090Effects of degraded speech processing and binaural unmasking investigated using functional near-infrared spectroscopy (fNIRS)PLOS ONE

Dear Dr. Zhou,

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.

Both reviewers felt that the manuscript is a significant contribution to our understanding of the neural basis of listening effort and spatial (un)masking. The larger concerns stem from questions about whether it is possible with fNIRS to spatially resolve regions of frontal cortex that are analyzed separately (i.e. IFG vs. DLPFC) and whether it is possible at all to measure activity from DMPFC given its depth. I agree with the recommendation of both reviewers that it would be better and technically more correct to lump these regions into "lateral prefrontal cortex" given that the main questions are about AC vs PFC and the fact that these data probably don't permit dissociation of sub-regions of PFC. 

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

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

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

Reviewer #1: Yes

Reviewer #2: Yes

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3. 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 #2: Yes

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4. 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 #2: 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: I have read the following submission carefully and consider it to be of good quality, hypothesis driven, and methodologically transparent. The article describes a speech in noise task in which listeners must attend to speech that is either unprocessed or degraded by an 8-channel vocoder. The key measures are from fNIRS centered on primary auditory centers in both hemispheres. The authors tested the hypothesis that two specific areas (left AC and left DLPFC) would carry different information regarding the nature of performing on the task, specifically regarding attention versus speech intelligibility factors during effortful listening. If there was a single flaw in the presentation of the paper, it would be too much consideration of listening effort when setting up the motivation or discussing the results. The authors measured subjective assessments of task difficulty as an indirect measure of listening effort for separate individuals using a different task (counting versus speech recognition), and no objective measure of the participants in the fNIRS test was used. Therefore, in my opinion, the space dedicated to its potential relevance is mostly conjecture and unnecessary for the stated hypotheses (ex. Line 523). That aside, the paper offers additional evidence of the specific roles that primary auditory centers have in speech-in-noise listening, and therefore, it is good contribution to the field.

The following are minor but should be addressed:

1) At various points (ex. Line 175), the authors refer to the poor fNIRS spatial resolution of previous studies (i.e., only 3-4 channels over certain areas). It’s unclear how that relates to the present paper other than maybe from counting dots in Figure 1. There’s a potential spot to mention the difference on Line 549.

2) Initially I flagged the stimulus methods for reducing the level of the masker by 3dB in the diotic condition; however, this was addressed in the discussion as a possible contributing factor to the results. It would be good, however, to provide a source reference for choosing 3 dB as the reduction on or around Line 235. Because this section specifically refers to loudness perception, and BLDELs can exceed 3, even 5 dB, for tonal stimuli, and it is common to have large individual variability, it would be helpful to acknowledge this upfront.

3) I may have missed it, but how accurate were listeners at counting color words and labeling odd/even for the fNIRS task? Were trials treated differently depending on their accuracy?

Others:

1) Title page has alphabet superscripts and numeral affiliations

2) I am not familiar with the in-text citation format that includes the first two of multiple authors (e.g., Line 108), but for consistency, there was at least two instances where the more traditional et al was used instead (line 560 or 636).

3) Typo: “unmaaking” (Line 97)

4) Delete “the” between “in….challenging conditions”

5) Line 228: This IEEE citation was not in the references

6) Line 230-231: I’m not sure what this is in parentheses after ER-2A phones – should be Etymotic?

7) Line 522: move “the” to after “between” (not before).

8) Line 633: change sNR to SNR

9) Line 715: The word “unfortunately” in this context sounds like the authors had a personal stake or interest in the results which I doubt is the case. I suggest removing this transition word.

Reviewer #2: The authors investigated the differential involvement of the auditory cortex (AC) and dorsolateral prefrontal (DLPFC) cortex in different listening conditions that manipulate the spatial configuration of noise (monotic vs diotic inducing spatial release from masking), signal-to-noise ratio as well as speech processing (using a vocoder simulation or left unprocessed). They found that DLPFC and AC showed different patterns of activities for SNR and vocoded speech manipulation but did not find evidence of spatial unmasking changing activities in these areas. Furthermore, they found a correlation with perceived task difficulty and neural activity in the left DLPFC. Overall, this is a well written manuscript that uses sophisticated fNIRS analyses and appropriate statistical approaches. Nevertheless, I have the following concerns:

Major:

1. It is unclear why the secondary question is there in the first place when the spatial resolution of fNIRS is clearly not sufficient to resolve these regions (as evident in the anatomical overlaps shown in Figure 1B). Perhaps the authors wanted to bring in the different literature to talk about listening effort and speech processing and thus needed to mention DLPFC and Inferior Frontal Gyrus (IFG) as potential regions of interest. Personally, I think it would just be cleaner to say that you have optodes over the lateral prefrontal cortex (and not make a delineation of dorsal vs ventral) and that the effects you see can be attributed to DLPFC and / or IFG. I think the authors already made the case in the discussion that ll545-7 "The lack of difference could also be due to the poor spatial resolution of fNIRS and measures from the three subregions could have still overlapped" so why present them in the first place?

2. I'm also doubtful that the medial prefrontal cortex is also part of the ROI because of how deep that structure is. As a reader, I also want to be convinced the the medial cortex can be captured in these optodes and only then bring in the literature regarding medial PFC in working memory, decision-making in your discussion.

3. p<0.09 should never be cast as "marginally non significant." Please remove this in the abstract and elsewhere in the manuscript.

Minor:

1. In-text citation looks funny when the authors are mentioned (e.g., Ln 108, it should be Hughes et al and not Hughes, Rowe and there are many instances throughout the MS that needs to be fixed).

2. Fig 5 is missing SNR labels

3. Ln 523: why Left AC here and not just AC?

4. Ln 633 Change sNR to SNR

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Reviewer #1: Yes: Erol Ozmeral

Reviewer #2: Yes: Adrian KC Lee

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Effects of degraded speech processing and binaural unmasking investigated using functional near-infrared spectroscopy (fNIRS)

PONE-D-21-30090R1

Dear Dr. Zhou,

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.

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Kind regards,

Andrew R Dykstra

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

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 #2: All comments have been addressed

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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 #2: Yes

**********

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

Reviewer #1: Yes

Reviewer #2: Yes

**********

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 #2: 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 #2: Yes

**********

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: All comments have been addressed. Please check new text for typos, e.g.:

Line 360: inlcuded -> included

Line 725: exisited -> existed

Reviewer #2: The authors have addressed all the comments except I urge them to consider these final recommendations: the DLPFC region in fig 1B is in general not different from f-ROI2 and f-ROI3. I suggest labeling it as f-ROI1 instead. Also, I suggest the following wordings on ll 260-262: The f-ROI1 most likely encompasses Broadman area (BA, 9 and 10), f-ROI2, BA 9 and 46, and f-ROI3, BA45 and BA47, which also likely covers the IFG

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: Yes: Erol J. Ozmeral

Reviewer #2: Yes: Adrian KC Lee, ScD