Content of review 1, reviewed on June 23, 2022
The article by Landry and colleagues investigates an understudied topic in the field of neuroplasticity. So far, only a few studies have looked at olfaction in deaf individuals. Landy and colleagues tested the olfactory detection threshold, odor discrimination, and odor identification using the Sniffin’ Sticks battery test. To disentangle olfactory and trigeminal skills, a timed odor localization and identification task was used. The group of deaf individuals was better at discriminating, identifying, and localizing odors than the group of hearing controls. This is a well-designed study and an interesting addition to the field. However, I have some serious concerns regarding the analysis of the data that need to be addressed. These critiques are described below.
Abstract:
Consider referring to the participants in your study with participants, not with subjects, as this term can be perceived as demeaning (Chalmers et al., 1999).
Introduction:
The literature review could be more comprehensive. While I understand that this is not a review article, several important studies have been neglected.
• olfaction in deaf individuals, e.g. (Sorokowska et al., 2020)
• improved visual abilities in deaf individuals, e.g. (Buckley et al., 2010; Codina et al., 2017; Shiell et al., 2014)
P4: the literature on changes in visual attention and spatial memory in deaf individuals is reviewed, and then it is explained that olfactory tasks such as odor identification and discrimination are associated with executive functions and semantic memory. Is there any evidence that executive functions and semantic memory is changed in deaf people compared to hearing people? If so, shouldn’t these skills be controlled for when comparing deaf and hearing individuals?
P4: It is stated that “[…] a delay in language acquisition in deaf individuals might have
influenced their understanding of the tasks, especially the congenitally deaf” While this may be the case in some instances, it is more likely that difficulties in understanding the task instructions arise when the task instructions are not provided in the native language of the participants.
Materials and Methods:
One serious concern regarding this study is the small sample size - even if it must be acknowledged that the participants are members of minority groups, and are not as easily recruited as, e.g., neuro-typical university undergraduate students.
P7: Try to avoid terms like 'the deaf', as this may be perceived as objectifying.
P9: It is not quite clear to me how the participants responded.
P11f: The reaction time data were analyzed with an ANOVA on the mean reaction times. Typically, reaction times are not distributed normally but show a positive skew. This should be taken into account when analyzing reaction time data. I would recommend analyzing the data using linear mixed-effects models (LMMs) and applying a transformation to the data or analyzing the data with Generalized linear mixed-effects models (GLMMs) (Lo & Andrews, 2015).
P12: to make it easier for the reader, state how many participants were in the group with a CI and how many people were in the group without a CI
P12: the term condition to describe the between-subjects factor is not intuitive, maybe change it to group?
Results:
P13/Figure2: The figure shows that several participants had a d’ value below 0, indicating a below chance performance, which could be due to response confusion, misunderstanding the task, or other (unknown) factors (Stanislaw & Todorov, 1999). This makes the interpretation of the data difficult and should be addressed.
Discussion:
P16: This sentence is a bit misleading: “In addition to better response sensitivity, the results of this study also indicate that deaf individuals responded faster on the localization and identification tasks, the latter correlating with response accuracy (Kéïta et al., 2013).” It suggests that accuracy and RTs were correlated in the present study. However, correlations were not assessed.
Buckley, D., Codina, C., Bhardwaj, P., & Pascalis, O. (2010). Action video game players and deaf observers have larger Goldmann visual fields. Vision Research, 50(5), 548–556. https://doi.org/10.1016/j.visres.2009.11.018
Chalmers, I., Jackson, W., & Carvel, D. (1999). People are ‘participants’ in research. BMJ, 318(7191), 1141–1141. https://doi.org/10.1136/bmj.318.7191.1141a
Codina, C. J., Pascalis, O., Baseler, H. A., Levine, A. T., & Buckley, D. (2017). Peripheral Visual Reaction Time Is Faster in Deaf Adults and British Sign Language Interpreters than in Hearing Adults. Frontiers in Psychology, 8. https://doi.org/10.3389/fpsyg.2017.00050
Lo, S., & Andrews, S. (2015). To transform or not to transform: Using generalized linear mixed models to analyse reaction time data. Frontiers in Psychology, 6. https://doi.org/10.3389/fpsyg.2015.01171
Shiell, M. M., Champoux, F., & Zatorre, R. J. (2014). Enhancement of Visual Motion Detection Thresholds in Early Deaf People. PLoS ONE, 9(2), e90498. https://doi.org/10.1371/journal.pone.0090498
Sorokowska, A., Hummel, T., & Oleszkiewicz, A. (2020). No Olfactory Compensation in Food-related Hazard Detection Among Blind and Deaf Adults: A Psychophysical Approach. Neuroscience, 440, 56–64. https://doi.org/10.1016/j.neuroscience.2020.05.033
Stanislaw, H., & Todorov, N. (1999). Calculation of signal detection theory measures. Behavior Research Methods, Instruments, & Computers, 31(1), 137–149. https://doi.org/10.3758/BF03207704
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© 2022 the Reviewer.
Content of review 2, reviewed on February 20, 2023
MAYOR
Figure2: Combing back to the issue of d’ scores below 0. As previously noted, this indicates below chance performance and should be addressed in the cleaning of the data, that is, these data points should be removed or looked further into. For example, if this response profile is indeed due to “response confusion with participants pressing the response button too quickly”, then shouldn’t trials with unreasonably fast RTs be removed? Unless this issue is addressed, the results should not be interpreted.
MINOR
P3/7: Try to avoid terms like 'the deaf/ the congenitally deaf', as this may be perceived as objectifying.
P3: “intermodal recruitment of the auditory […]” – Do you mean crossmodal recruitment?
P3: “Therefore, like these two modalities, it can be hypothesized that hearing loss also leads to a compensation of the olfactory function.” – It is not quite clear here what you mean by these two modalities? The tactile and visual modality?
P5: “The duration of deafness and auditory rehabilitation by means of a cochlear implant (CI) are also factors known to influence the extent of neuroplasticity in impaired hearing individuals (Kral et al., 2016).” – Should be “hearing impaired individuals”.
P12f: It is stated that the interaction of task*group is not significant but that there was a significant effect of group. Yet, the post hoc tests assess the factor of group separately for the two tasks.
It is stated that “More recently, a study showed that the deficit in deaf children was mediated by the level of receptive vocabulary (Merchan et al., 2022)” – It is not quite clear here which deficits you are referring to.
“The latter has been found to correlate with response accuracy (Kéïta et al., 2013).” – I am not quite sure what is meant with the latter? Do the response times on the identification task correlate with the response accuracy?
For the deaf participants, there were test on attention, visual memory, and fluid reasoning. Are those tests also available for the hearing individuals? If so, could differences between the two groups on those measures explain the group differences?
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© 2023 the Reviewer.
Content of review 3, reviewed on July 31, 2023
I have carefully reviewed the article, and I appreciate the effort the authors have put into addressing the previous comments and concerns. While I understand the author’s perspective on keeping all data points to avoid introducing bias, I still believe it is essential to address the issue of d' scores below 0 in a comprehensive manner.
I agree with the authors that small negative values may be indicative of a "true" d' near zero, i.e. "true" chance performance. However, some of the d’ scores were even smaller than -1, which is unlikely to reflect chance performance and instead may be indicative of other issues, for example that participants did not follow the task instructions appropriately or encountered some other issues. This can potentially compromise the validity and reliability of the data. To address this concern, I suggest performing a thorough examination of the participants with d' scores below 0 to identify potential sources of error, such as "response confusion with participants pressing the response button too quickly".
If there is evidence to support the idea that unreasonably fast reaction times are driving the d' scores below 0, those specific trials should be removed from the analysis. Alternatively, if there are other identifiable patterns or causes contributing to the below-chance performance, they should be investigated and reported in the article.
In addition to this, I suggest to report the analyses with data points where d’ < -0.5 excluded in the supplement. By including these supplementary analyses, the authors could demonstrate the robustness of their findings and address any potential concerns about the influence of extremely low d' scores on the overall results.
My main concern is that the interpretation of the results could be misleading if the issue of d' scores below 0 is not addressed. By acknowledging and thoroughly examining this aspect of the data, the validity and reliability of the findings can be strengthened, providing a more accurate representation of potential group differences.
There were also some minor points that should be addressed:
p. 5/l. 1: “Odorant” should be “Odorants”
p. 56: “More recently, a study has highlighted the influence of receptive vocabulary level in explaining the lower performance observed in deaf children, rather than attributing it to sensory deprivation (Merchan et al., 2022).” Here, it is still not clear what this lower performance is referring to (i.e. to the ability to suppress the interference of distractors).
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© 2023 the Reviewer.
Content of review 4, reviewed on November 19, 2023
The authors have successfully answered all my concerns and suggestions. I therefore suggest acceptance for publication in European Journal of Neuroscience
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© 2023 the Reviewer.
References
Catherine, L., Rim, N., Marie, S., Francois, G., Lecuyer, G. F., Franco, L., Johannes, F. 2024. Behavioural evidence for enhanced olfactory and trigeminal perception in congenital hearing loss. European Journal of Neuroscience.