PONE-D-20-12685

Visual attention towards food during

unplanned purchases – A pilot study using mobile eye tracking technology

PLOS ONE

Dear Dr. Hummel,

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.

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Zhifeng Gao

Academic Editor

PLOS ONE

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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: Partly

Reviewer #2: Partly

Reviewer #3: Yes

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

Reviewer #1: No

Reviewer #2: No

Reviewer #3: Yes

**********

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: No

Reviewer #2: No

Reviewer #3: No

**********

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

Reviewer #3: Yes

**********

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: Referee Report for PONE-D-20-12685

Visual attention towards food during unplanned purchases— A pilot study using mobile eye tracking technology

This papers uses a field experiment to examine the relationship between individuals’ weight status, food energy density, and visual attention during unplanned purchases. Results indicate that participants with higher BMI show an attention bias towards high-calorie foods compared to low-calorie foods. The opposite effect is found for subjects with lower BMI.

There is much to like about this paper. It addresses a very important public health problem (unhealthy eating) in a novel way. It considers distributional effects across relevant groups (i.e. BMI categories), which are generally understudied. Having said that, I have major concerns which are mainly related to the lack of information on the experimental procedures and the small number of observations. Please find my concerns below.

Main Comments

1. My biggest concern relates to sample size. There are two weight classifications (high and low BMI), with less than 10 subjects in each category. This is a low number unlikely to be supported by an ex ante power calculation. I understand that obtaining a large number of participants in a real setting, particularly subjects with high BMI, can be somewhat of a challenge. But any statistical analysis based on such few subjects would, at best, be highly preliminary. I would encourage the authors to increase their sample size significantly.

2. Subjects are classified into two weight categories based on self-reported measures of height and weight. Since BMI classification is a main component of this study, relying on self-reported measures is not ideal. If the authors are to increase sample size, I suggest they look into ways to collect weight and height measures during the experiment; for example, experimenters could collect these measures at the end of the last shopping trip, right before payment.

3. I find the description of experimental procedures to be exceptionally sparse. When was the eye tracking data collected? Was the same weeks used for all subjects? (e.g. eye tracking data was collected for all subjects in weeks 2 and 4), Did subjects knew they would be using eye tracking glasses during those trips beforehand?

4. How many online questionnaires were collected by subject and when were these implemented? What information did they collect besides socio-economic characteristics? This is important because the type of questions could prime subjects and affect their subsequent purchasing behavior. For example, it would make a big difference if the self-reported weight and height measures were collected at the beginning or at the end of the experiment as asking for subjects’ weight might prime them towards specific food products or product quantities.

5. Who are the participants? The authors mentioned that socio-economic characteristics were collected in the online survey (e.g. gender, age, income); however they do not provide any description of the sample population. I find it a significant omission for an experimental paper to not present a summary of the demographic profile of the sample. This is not necessarily a criticism of the experiment procedures, but rather the written summary of the procedures. I suggest the authors provide a table with a summary of the demographic profile for all the sample and by BMI category (normal weight and overweight/obese).

6. Each participant received a 50 € voucher as compensation fee at the end of the experiment. Was there another incentive throughout the experiment? If subjects knew they would be receiving the voucher for completing the study, there was no incentive for them to truthfully report their preferences during each shopping visit (i.e. while making shopping lists and purchases). The compensation should have been split into weekly payments.

7. Why was participation restricted to households with 2-5 members? Were participants shopping by themselves? This is important as the presence of a second individual might steer participants toward specific products. For example, Papoutsi et al. (2013) show that children’s pestering power strongly affects parents in making unhealthier food choices. I suggest the authors use data from the online questionnaires (e.g. Who joined the trip?) to control for the number of people in the shopping trips as well as household size.

8. Subjects were asked to write a weekly shopping list and collect grocery receipts for four weeks. When were the receipts and lists collected by the experimenter? If these were collected at the end of the experiment, subjects had the opportunity to revise their shopping lists as much as they wanted. Also, there is the possibility that after 1-2 weeks subjects got an idea of the purpose of the experiment and started adjusting their behavior. I suggest the authors control for week effects.

9. The results in Table 1 and Table 2 should be split by BMI and energy density. For example, I would like to see the number of LC and HC unplanned purchases for each BMI category, same for all statistics reported in Table 2. This might cause the significant effects in Table 2 to disappear due to the small sample size, which highlights the need to collect more data.

10. Throughout the paper, there is no mentioning of the type of statistical tests used (t-tests, one or two-sided, etc.) when statistical analysis is performed. This information needs to be clarified, particularly in Tables and Figures. The authors refer to p-values in Table 2 and Figure 2– what are the statistical tests? The authors should include the relevant missing information in the table notes and figure captions so that they are self-contained.

11. The analysis is generally lacking in statistical rigor. The results are primarily based on pairwise-comparison tests and I think there are several important factors that need to be controlled for using model specifications/regressions. For example, I would strongly encourage the authors to explore whether the results vary over time (by week); are the findings consistent if one looks at early purchases (e.g. first 2 weeks) vs. later purchases (2 latest). The authors should also control for time-of-the-day effects and individual characteristics such as hunger level, gender, household size, income, eating habits.

12. Related to my previous comment, the authors are using the observations (unplanned purchases) made by the same individual in different weeks as independent observations. I suggest they consider using models for panel data that cluster the standard errors at the individual level and control for all factors described in the previous comment. They can also test for interaction effects between weight status and energy density using these models rather than ANOVA tests (or complement both).

13. The authors compare attention bias towards the bought product and the labels. What information was provided in the shelf labels? If the only information provided was the product price, a possible explanation for the lower amount of time spent looking at the labels compared to the product could be the familiarity with this attribute. It is reasonable to think that since individuals compare product prices on a regular basis, they might not need as much time to process price information. I think the authors could make more use of the eye tracking data by creating AOIs for the product labels instead of shelf labels. They could explore whether subjects fixate longer on calorie content or health claims such as low-fat, sugar reduced, fat-free, etc. and relate this to unplanned food choices.

14. It would have been interesting to see more results related to heterogeneity of unplanned purchases/visual attention of individuals who were more/less hungry according to the scale the authors collected. There is a vast literature on how hunger might produce different effects, and this paper could have something to say about this.

Other comments

1. The relationship between visual attention and food choice across BMI categories is an important contribution that has been highly understudied. Only few studies that have examined such distributional effects (Segovia et al. 2019). This is worth stressing more in the paper.

2. The authors should be consistent in the terminology used for BMI categories, sometimes they refer to the groups as high vs. low BMI, sometimes as BMI<25 vs. BMI>25, and other times as normal weight vs. overweight/obese.

3. Are there underweight subjects in the sample? (BMI< 18.5). If so, they should not be part of the normal weight group.

4. Page 15, lines 357-358: sentence makes no sense. Please edit.

5. The limitations of the study can be discussed in the conclusions section, no need for a separate section.

References

Papoutsi, Georgia, Rodolfo Nayga, Panagiotis Lazaridis, and Andreas Drichoutis. "Nudging parental health behavior with and without children's pestering power: Fat tax, subsidy or both?." (2013).

Segovia, Michelle S., Marco A. Palma, and Rodolfo M. Nayga Jr. "The effect of food anticipation on cognitive function: An eye tracking study." PloS one 14, no. 10 (2019): e0223506.

Reviewer #2: This paper investigated the link between visual attention and unplanned food purchase decisions in a real-world environment, while incorporating conceptually relevant variables such as participants’ weight status and cues presented on food labels such as energy density. The authors adequately reviewed the literature and formed the hypotheses in a manner that help to shed light on earlier inconsistencies in the literature on this topic. An important contribution, as the authors also highlighted, is the use of visual attention data generated in a real-world environment as opposed to a controlled laboratory. On the flip side, experimenting in a real-world setting represents a host of challenges that can interfere with the investigation that aims to link visual attention to other individual-specific characteristics or product-specific attributes. Additionally, while the introduction of the paper is well prepared, there are some shortcomings in the description of the experimental procedures. Please see my review comments below.

Comments

- The experiment design and hence the findings suffer from a major issue due to the product arrangement in a supermarket. As indicated in Lines 313-315, if the LC foods are offered in the first section, while the HC foods are located in the later sections. This gives a basis to consider that consumers may face less time pressure or constraints in choosing LC foods (i.e., beginning of the shopping experience) and more time pressure/constraint in choosing HC food (i.e., toward the end of the shopping experience). Because of this arrangement, consumers may spend more time and pay more visual attention to LC foods, while paying less visual attention to HC foods. In other words, we don’t know for sure whether the differences in visual attention between HC and LC foods (and across BMI groups) were caused by the product arrangement or the differences in energy density that the authors tried to identify in the study. Generalizing statement such as “There was a tendency across all participants to look at low energy density food longer and more often.” (Lines 12-13) need to be interpreted with caution. The authors may want to acknowledge this as a major limitation of this study.

- Lines 283-287: The authors compared fixation duration between low BMI participants for LC, high BMI participants for LC, and low BMI participants for HC. From my point of view, the authors should conduct a complete between-group and within-group comparison to capture the interaction between BMI and energy density on all VA measures. Using fixation duration as an example, between-group comparison should be conducted for a) between low BMI participants’ fixation duration for LC foods, and high BMI participants’ fixation duration for LC foods, b) between low BMI participants’ fixation duration for HC and high BMI participants’ fixation duration for HC. Within group comparison should be conducted for a) between low BMI individuals’ fixation duration for LC and HC, b) between high BMI individuals’ fixation duration for LC and HC foods.

- The authors may consider adding a table reporting the demographic variables comparison between the low and high BMI groups as we know BMI is closely related to individual characteristics such as age and income. This information is completely missing in the current version. Demographic information is particularly important for this study because the sample size is very small.

Other comments or clarification needed

- Section 2.4. The authors identified consumers’ unplanned purchases by checking their grocery receipts for the past four weeks. As shoppers ourselves, we know perfectly that there are times when last-minute items pop up when we are already at the store, even with a shopping list. Since this is a major variable of interest and used to test two of the three hypotheses, I have concerns about the reliability of this procedure. Please comment.

- Section 3.1. The number of participants in this study is a concern. I am well aware of the difficulties associated with implementing eye tracking studies, especially at a grocery store. However, without reporting the full picture of the visual attention variable statistics and demographic characteristics, it is difficult to make a judgement about the reliability of the results.

- Lines: 129-131: You are listing three different measures - maintained attention, counts for fixations, and counts for visits. Then, in the next sentence, you are saying both (referring to two) measures are acceptable measures to be included in the analysis. I have no doubt that visual attention variables are relevant in such analyses. However, there are important distinctions between fixation counts (within an AOI or across AOIs) and AOI visits. One can measure fixation counts within an AOI during a single or multiple visits. The other measure, visit counts, can be used (e.g., comparing two different AOIs) without incorporating any fixation counts. Please clarify the exact measure that you are using.

- Section 2.3. By “maintained attention towards food” are you referring to fixation duration as used in Tobii Pro manuals?

- Section 3.3. Heat map grid:

o Plot C – Duration for fixations and visits. Is this the duration of the total number of fixations and total number of visits within an AOI/grid? Again, the number of fixations and number of visits are conventionally defined differently. Unless you are assuming different definitions in this particular study. Please explain.

o Plot D – Again, I am not sure how the number of fixations and visit can be measured as one variable. One can visually attend to (visit) an AOI, and fixate multiple times during that one visit. Please clarity.

o How was the irregular size of the product spaces on real store shelves mapped into the current grid system? If the space above or below the purchased product includes more than one product, how were situations like those handled. I would be interested in examining the actual heatmaps and the manual mapping of the fixations and the image of the purchased product shelves.

- Section 2.1. When was the experiment conducted? Was the recruitment done right at the store?

- Section 3.2.

o What is the measure of shelf height in Table 2?

o Is the unplanned purchase duration (in seconds) measured when taking the item from the shelf and placing in the cart?

o It would be useful to include a column that defines these variables.

o First time use of VAS in table 2. Please explain what it means.

Reviewer #3: The study evaluates the visual attention for unplanned purchases in a grocery store using mobile eye tracking technology and related the visual attention to the energy density of the food. I believe this is an interesting study. Some aspects of the study were not clear to me and are included in my comments to the authors.

ABSTRACT

• Line 9: attention bias. If attention is influenced by energy density and weight status, why is it necessarily a bias?

• Line 13: Can you explain more about the interaction: “Interaction effects between weight status and energy density for fixation and visit duration were found”

INTRODUCTION

• Line 22, can you better define unplanned purchases?

• Line 33: what about food purchases, how many are unplanned?

• Line 52: initial orientation? What do you mean?

• Line 55: “Gearhardt et al. (2012) showed a decreased initial attention towards fried food for participants with higher BMI”, decreased compared to what?

• Line 69: you hypothesize that is differs, but can you be more specific? Do you think VA will be higher or lower?

• Line 87: In what way is there in interaction? What is the direction? Can you be more specific of your H3?

METHOD

• How did you know which purchases were unplanned?

• Line 36: why no constraints? What do you mean by this?

• Line 127: what is the measurement error etc.

• Line 132: “first fixation”, do you mean “time to first fixation”?

• Line 149-150: what is the disadvantage using no overlap? What about peripheral vision? What about eye tracking errors? Should it not be accounted for a bitmore by making the AOIs a bit larger than the products themself?

RESULTS

• Was there a relation between attention and choice and if so, was this influenced by the weight status?

• Line 177: “ During these trips, 16 participants showed unplanned purchase behavior and three participants showed no unplanned purchase behavior at all” . How do you know it is unplanned? How did you measure this? How did you define it?

• Line 218 identi-fied: typo

• The product in the middle is row P. Did each isle have 7 shelves? What if a chosen product is on the bottom shelf, then there is no P-1, P-2, P-3. It is not clear how you addressed this.

• Line 222: “The product one row above”. Do you mean one shelf higher?

• Line 261: “ normal weight noticed the food of their choice earlier and looked longer at it than participants with overweight or obesity”. Due to this result, you confirm H1. However in H1 you only state that the VA would differ. Did you have a specific hypothesis how it would differ? In which case would it be higher? Does the results match this hypothesis?

• Line 235-236: “ While information labels and price tags were on average focused by three spontaneous purchase decisions (M = 3.1, SD = 5.1), the products themselves were focused more than twice as often (M = 7.3, SD = 11.9).” This sentence is not clear. The labels and price tags were focused by purchase decisions? Please rephrase.

• Check, sometimes VA and sometimes in full “Visual attention”. Please be consistent in the use of the abbreviations.

CONCLUSION

• Line 305: “Participants with normal weight made 76% of the unplanned purchases”. Again, I wonder how you defined unplanned purchases and how this was measured.

• What are the results for people with overweight? Does your study provide insight in how we can help them to attend to energy information?

• What about planned food purchases?

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6. 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: No

Reviewer #2: No

Reviewer #3: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

Attachments

Attachment

Submitted filename: PONE-D-20-12685_reviewer1.pdf

PONE-D-20-12685R1

Visual attention towards food during

unplanned purchases – A pilot study using mobile eye tracking technology

PLOS ONE

Dear Dr. Hummel,

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.

To give you timely response, we didn't wait for one of the reviewers' comments. Please just make your revision based on the comments from the two reviewers. 

Please submit your revised manuscript by Dec 19 2020 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: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

We look forward to receiving your revised manuscript.

Kind regards,

Zhifeng Gao

Academic Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

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 #2: (No Response)

Reviewer #3: (No Response)

**********

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 #2: (No Response)

Reviewer #3: Yes

**********

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

Reviewer #2: (No Response)

Reviewer #3: 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 #2: (No Response)

Reviewer #3: No

**********

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 #2: (No Response)

Reviewer #3: 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 #2: (No Response)

Reviewer #3: The authors have has improved the manuscript. However, a few small questions still remain.

• You mention that you changed attention bias to visual attention. However, this is not adjusted everywhere (for example line 281). Please explain.

• The product in the middle is row P. Did each isle have 7 shelves? What if a chosen product is on the bottom shelf, then there is no P-1, P-2, P-3. It is not clear how you addressed this. You mention that a product at the bottom shelf, will not have P-1, P-2 etc. How did this impact the generation of Figure 1?

**********

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 #2: No

Reviewer #3: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

Attachments

Attachment

Submitted filename: PLOS One reviewR2.docx

PONE-D-20-12685R2

Visual attention towards food during

unplanned purchases – A pilot study using mobile eye tracking technology

PLOS ONE

Dear Dr. Hummel,

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.

It seems that there is one issue of the experimental design that cannot be fixed. Please carefully address this issue and the related reviewer's comments. I understand the difficulty of considering all the factors when running an experiment in field, but the limitations should be clearly discussed so readers understand the potential issues. 

Please submit your revised manuscript by Feb 20 2021 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: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

We look forward to receiving your revised manuscript.

Kind regards,

Zhifeng Gao

Academic Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

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 #2: (No Response)

Reviewer #3: All comments have been addressed

**********

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 #2: Partly

Reviewer #3: Yes

**********

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

Reviewer #2: Yes

Reviewer #3: 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 #2: Yes

Reviewer #3: Yes

**********

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 #2: 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 #2: 1) You did briefly discuss the issue of fixed arrangement at the end of the manuscript. I also read in your response the following: “That’s why we controlled for this influence and discussed this issue at the end of the manuscript.” However, my understanding is that you did not control the influence of fixed arrangement in your experiment. Please clarify your statement.

One way to control the influence of fixed arrangement would be through randomizing the starting point of your participants’ shopping experiences. For example, if low caloric foods were located in the front sections of the store (and high caloric foods in the back), you could instruct half of your participants to start shopping from the front. The other half of the participants would then start shopping from the back of the store. This would ensure that all of your participants didn’t start by paying attention to and purchasing low caloric foods first, thus controlling for the fixed arrangements. Does this make sense?

2) Thank you for taking into consideration of my suggestion and conducted additional analysis using dichotomous variables.

First off, I want to note that the presentation of your regression results were messy. You should preview your response file before submitting. Because the results shown in Tables 1a, 1b, 2a, and 2b are not really in a table format, it took me some time to figure out which number corresponds to what. If my understanding is correct, Model 1 in Tables 1a, 1b, 2a, 2b incorporated interaction terms and thus parallel/comparable to Table 3 in your manuscript.

By comparing Model 1 results with Table 3, I understand that using dichotomous variables does not significantly alter the results and thus all the results in Table 3 are retained (i.e., MBI, energy density as continuous variables).

However, you may already realize that your Tables 1a, 1b, 2a, 2b results are actually more consistent/comparable with Figure 3. This is because intercepts in your regression measure exactly the FD, VD, FC and VC of your base group, adding (or subtracting if negative) the coefficients of BMI, and ED provides estimates for the other group.

Figure 3 are plots based on raw data, while results in Tables 1a, 1b, 2a, 2b control for individual characteristics. Hopefully this explanation make sense to you why I wanted to see regression results based on dichotomous groups.

Reviewer #3: (No Response)

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Reviewer #2: No

Reviewer #3: No

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Attachments

Attachment

Submitted filename: PLOS One reviewR2.docx

Visual attention towards food during

unplanned purchases – A pilot study using mobile eye tracking technology

PONE-D-20-12685R3

Dear Dr. Hummel,

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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Kind regards,

Zhifeng Gao

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 #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 #2: Yes

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

Reviewer #2: 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 #2: No

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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 #2: (No Response)

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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 #2: Thank you for making efforts to clarify my last comments. The responses are satisfactory, and I think the present version is acceptable.

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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.

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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 #2: No