Too Bright to Focus? Influence of Brightness Illusions and Ambient Light Levels on the Dynamics of Ocular Accommodation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Firstly, congratulations to the authors on the publication. It is a good investigation, and we hope that with the comments in this review it will achieve the quality required for publication.

 

METHODS

 

-Why was Conlon's questionnaire used to collect symptoms? Were other options considered, such as Quality of Vision (QoV), which also collects photic phenomena, or other questionnaires?

 

RESULTS

 

-It would be helpful to the study, even if only through supplementary material, to present the demographic data of the sample, as well as the visual and refractive values and the accommodative test values.

 

-It would be advisable for the p-values of the comparison between groups to also appear in Tables 1 and 2.

 

-Correlations should be made between the values of the parameters obtained in this study.

 

Author Response

Firstly, congratulations to the authors on the publication. It is a good investigation, and we hope that with the comments in this review it will achieve the quality required for publication.

We sincerely appreciate your comments and the time you devoted to reviewing our manuscript

METHODS

Why was Conlon's questionnaire used to collect symptoms? Were other options considered, such as Quality of Vision (QoV), which also collects photic phenomena, or other questionnaires?

We appreciate the suggestion to consider alternative questionnaires such as the Quality of Vision Questionnaire (QoV). In our study, we chose to employ the Conlon questionnaire for both methodological and conceptual reasons. First, the Conlon questionnaire was specifically developed and validated to assess visual symptoms related to reading, contrast, and sensitivity to visual patterns or stimuli, which aligns closely with the objectives of our research. In particular, our study focuses on the presence of visual symptoms associated with visual discomfort and fatigue arising from brightness and contrast stimuli, aspects directly addressed by this questionnaire. Furthermore, the Conlon questionnaire has a well-established track record in optometry and visual ergonomics research and has proven useful for assessing visual comfort in experimental contexts (e.g., Conlon et al., 1999; Conlon et al., 2001), including previous studies examining variables closely related to ours, such as accommodative and pupillary dynamics (e.g., Redondo et al., 2023; Vera et al., 2022 and 2023). For these reasons, we consider its use both appropriate and justified for our research objectives.

Conlon, E. G., Lovegrove, W. J., Chekaluk, E., & Pattison, P. E. (1999). Measuring visual discomfort. Visual Cognition, 6(6), 637-663.

Conlon, E., Lovegrove, W., Barker, S., & Chekaluk, E. (2001). Visual discomfort: the influence of spatial frequency. Perception, 30(5), 571-581.

Redondo, B., Vera, J., Molina, R., & Jiménez, R. (2023). Less is more: optimal recording time for measuring the steady-state accommodative response. Clinical and Experimental Optometry, 106(1), 20-28.nses for myopia control. Contact Lens and Anterior Eye, 46(1), 101526.

Vera, J., Redondo, B., Ocaso, E., Martinez‐Guillorme, S., Molina, R., & Jiménez, R. (2022). Manipulating expectancies in optometry practice: Ocular accommodation and stereoacuity are sensitive to placebo and nocebo effects. Ophthalmic and Physiological Optics, 42(6), 1390-1398.

Vera, J., Redondo, B., Galan, T., Machado, P., Molina, R., Koulieris, G. A., & Jiménez, R. (2023). Dynamics of the accommodative response and facility with dual-focus soft contact lenses for myopia control. Contact Lens and Anterior Eye, 46(1), 101526.

RESULTS

It would be helpful to the study, even if only through supplementary material, to present the demographic data of the sample, as well as the visual and refractive values and the accommodative test values.

We sincerely appreciate your suggestion. In the revised version of the manuscript, we have incorporated the demographic data of the sample, as well as measures of visual symptoms, visual acuity, refraction, and accommodative function in a table included in the supplementary material (see Table S1) following your recommendation. We refer to this table in the manuscript in the first paragraph of the “Results” section (see lines 273–276).

It would be advisable for the p-values of the comparison between groups to also appear in Tables 1 and 2.

We appreciate your comment regarding the inclusion of p-values in Tables 1 and 2. Upon consideration, we believe that adding these values directly to the tables would complicate their readability and interpretation, as the p-values arise from multiple within-subject comparisons between factors rather than a single between-group comparison. For this reason, we consider it clearer and more appropriate to present the p-values only in the text, highlighting those that are significant, as has been done in the current version of the manuscript. Nonetheless, we understand the relevance of your suggestion and remain attentive to your guidance. If you consider that there is a straightforward and clear way to incorporate the p-values into the tables without overloading them, we would be willing to implement it following your recommendation.

Correlations should be made between the values of the parameters obtained in this study.

We greatly appreciate your suggestion to perform correlations between the parameters obtained in the study. In the revised version of the manuscript, we have included these correlations in a table (Table S2) within the supplementary material, making this additional information available. However, we have not incorporated these analyses into the main “Results” section of the article, as correlation analysis was not part of the objectives originally established for this study. We refer to this table in the manuscript in the first paragraph of the “Results” section (see lines 276–277).

Reviewer 2 Report

Comments and Suggestions for Authors

Unfortunately, I don't think this is a strong submission. There are several issues.

1) The research questions themselves are not very important. Why do we care, for example, whether an illusion of brightness might affect accommodation? More specifically, why do we care if a brightness illusion affects accommodative gain and/or variability?

2) Some of the manipulations are not what should have been done. For example, the authors have manipulated average luminance and contrast in a confounded fashion. The low luminance stimulus was also the low contrast one. 

3) They presented two versions of a brightness illusion (see Fig 1). One version makes the central area appear brighter than the background and the other version does not. But this manipulation is also confounded because the bright one also has a blurred contour near the fixation point while the not-bright one does not. So they have confounded apparent brightness and blurriness. 

4) They report accommodative lag using an unusual definition that obscures some of the data. Their definition of lag is the difference in diopters between the response to a static stimulus and the response to a dynamic one. Usually lag is defined as the difference between the accommodative stimulus (that is, the demand) and the accommodative response. Because they did this, we cannot see what the effect of the various stimulus manipulations is on accommodation accuracy per se. By the way, if the lag they report in Table 1 is positive does that mean that the accommodative response to the static target was nearer than the response to the dynamic target? Or does it mean the opposite?

5) They manipulated color but did not consider what the expected effect is due to the eye's longitudinal chromatic aberration. That aberration should have affected the response to the static and dynamic stimuli alike, but we can't see such an effect because they report the difference between responses to static and dynamic.

6) Finally and importantly, the results (see Table 1) are basically that there is no effect of any of their manipulations except that higher luminance leads to smaller pupils and this is widely known already. The largest difference in accommodative lag (as they defined it) is 0.06 diopters which is much smaller than the accuracy of the autorefractor and much smaller than the depth of focus of the human eye. 

Author Response

Unfortunately, I don't think this is a strong submission. There are several issues.

We sincerely appreciate your observations and the time you have dedicated to reviewing our manuscript. Below, we would like to address each of the points you raised, with the aim of clarifying certain methodological and conceptual aspects that may not have been made sufficiently explained.

1) The research questions themselves are not very important. Why do we care, for example, whether an illusion of brightness might affect accommodation? More specifically, why do we care if a brightness illusion affects accommodative gain and/or variability?

We understand your concern regarding the importance of investigating whether a brightness illusion can affect ocular accommodation. The manipulation of the stimulus, using one that is susceptible to generating a brightness illusion and another that does not elicit such an illusion (control), serves to examine whether the dynamics of the visual system behaves in a similar or different manner under these conditions. Stimulus manipulation has revealed results showing that “Brightness illusions enhanced perceived brightness but reduced visual comfort, especially in low-light environments. These findings highlight the relevance of visual ergonomics in digital screen use, supporting guidelines that discourage bright screen exposure in dark settings” (see lines 660-663).

This, in turn, may be relevant given that accommodation is a key component of visual fatigue during the use of electronic devices. Understanding how specific stimuli (with or without enhanced brightness) or ambient lighting conditions affect the stability of this visual function may have direct implications, for instance, for the ergonomic design of displays (see lines 573-581). Furthermore, dynamic clinical evaluation of accommodation in such contexts is not commonly undertaken, an aspect that we believe was important to address through our study.

Therefore, we believe that the study provides value to the scientific community, as it contributes to understanding how purely subjective perceptual phenomena can modulate physiological responses (i.e., pupillary and accommodative) and may have both theoretical and applied implications (for example, in visual design or interface development; see lines 578-581). We have attempted to justify these aspects both in the “Introduction” (see lines 66-80) and in the “Discussion” (see lines 582-596) of the manuscript.

2) Some of the manipulations are not what should have been done. For example, the authors have manipulated average luminance and contrast in a confounded fashion. The low luminance stimulus was also the low contrast one. 

Thank you for pointing out this aspect, since it is important to clarify the experimental manipulation and avoid potential misunderstandings. In our experimental design, the stimulus you refer to as low luminance (which we describe in the study as the “non-bright stimulus”) was also presented under the low-contrast condition. The brightness illusion was controlled through the design or configuration of the stimulus, while ambient illuminance (room lighting) and source illuminance (screen) determined the two contrast conditions. Therefore, as you point out, the low-luminance stimulus (non-bright, as we describe it) was presented both under the low luminance-contrast condition (photopic condition) and under the high luminance-contrast condition (mesopic condition). This was intentionally manipulated in the experimental design, as the aim was to simulate common environmental conditions of screen use (lit room vs. dark room), combined with two types of stimuli (presumably brighter vs. less bright). Below, we indicate the text in which we explain this:

“Room luminance was adjusted relative to the screen brightness to modify the contrast ratio, resulting in two experimental conditions: a low contrast ratio, when the room was illuminated (photopic ambient condition); and a high contrast ratio, when the room lights were turned off, leaving only ambient light emitted from the screen (mesopic ambient condition)” (please, see lines 134-138).

3) They presented two versions of a brightness illusion (see Fig 1). One version makes the central area appear brighter than the background and the other version does not. But this manipulation is also confounded because the bright one also has a blurred contour near the fixation point while the not-bright one does not. So they have confounded apparent brightness and blurriness. 

The design of the stimuli in our study was based on those used in previous research (Laeng & Endestad, 2012; Suzuki et al., 2019), in which the spatial configuration and the arrangement of the intensity gradient of the stimulus elements are what determine whether the brightness illusion is generated or not. In our study, we did not intend to manipulate blur, nor was it a variable of interest in this experiment. We acknowledge, however, that the stimuli may have produced secondary effects of perceived blur, which is a relevant aspect that we will add to the “Discussion” as a potential limitation and an interesting avenue for future research (please, see lines 627-632).

4) They report accommodative lag using an unusual definition that obscures some of the data. Their definition of lag is the difference in diopters between the response to a static stimulus and the response to a dynamic one. Usually, lag is defined as the difference between the accommodative stimulus (that is, the demand) and the accommodative response. Because they did this, we cannot see what the effect of the various stimulus manipulations is on accommodation accuracy per se.

We greatly appreciate this observation and understand the concern regarding the definition used to calculate accommodative lag. Indeed, the most common definition in the literature is to calculate lag as the difference between the accommodative stimulus (accommodative demand, in D.) and the measured accommodative response (also in D.). We acknowledge that the explanation provided in the manuscript regarding the definition of accommodative lag was not sufficiently clear. In the revised version, we have rewritten this section to improve clarity and ensure that the calculation and interpretation of this measure are more transparent for the reader (see lines 232-240).

Additionally, we would like to clarify this concept here by providing an example: a subject with a mean accommodative response of 1.85 D. at 50 cm, and with a residual refractive error of +0.10 D. (after being optically corrected), has a near refractive state of 1.75 D. Therefore, considering that the ideal response is -2.00 D (40 cm), this subject has a lag of accommodation of 0.25 D. (i.e., -1.75 – [-2.00] = 0.25 D.). This approach has been previously employed in studies using open-field autorefractors such as the WAM-5500, which was also used in our research (see, for example, Redondo et al., 2020; Vera et al., 2022, cited in our manuscript; and Poltavski et al., 2012)

Redondo, B., Vera, J., Molina, R., Garcia, J. A., Catena, A., Muñoz-Hoyos, A., &     Jimenez, R. (2020). Accommodation and pupil dynamics as potential objective predictors of behavioural performance in children with attention-deficit/hyperactivity disorder. Vision Research, 175, 32-40.

Vera, J., Redondo, B., Ocaso, E., Martinez‐Guillorme, S., Molina, R., & Jiménez, R. (2022). Manipulating expectancies in optometry practice: Ocular accommodation and stereoacuity are sensitive to placebo and nocebo effects. Ophthalmic and Physiological Optics, 42(6), 1390-1398.

Poltavski, D. V., Biberdorf, D., & Petros, T. V. (2012). Accommodative response and cortical activity during sustained attention. Vision Research, 63, 1-8.

By the way, if the lag they report in Table 1 is positive does that mean that the accommodative response to the static target was nearer than the response to the dynamic target? Or does it mean the opposite?

Regarding the interpretation of the positive values in Table 1, a positive accommodative lag value indicates that the accommodative response is delayed or falls behind the accommodative stimulus (in this case located at 50 cm). As shown in Table 1, the greatest lag of accommodation (and therefore, less accommodative response) corresponds to the “Low Contrast (Photopic Condition), yellow non-bright stimulus” (0.70 ± 0.36 D.; see the comments referring to these results in the first paragraph of section 3.1).

5) They manipulated color but did not consider what the expected effect is due to the eye's longitudinal chromatic aberration. That aberration should have affected the response to the static and dynamic stimuli alike, but we can't see such an effect because they report the difference between responses to static and dynamic.

We thank the reviewer for raising the issue of longitudinal chromatic aberration (LCA). We would like to provide some explanation concerning the possible influence of LCA. Based on our assessment, it is unlikely that LCA predominated in our specific stimuli:

• First, participants fixated a small, achromatic central cross (2 mm) placed at the very center of each stimulus; this was identical across conditions and was the element intended to drive the accommodative response. The chromatic content (blue/yellow) was confined to surrounding, parafoveal structures of the illusion. Thus, the foveal stimulus that provides the strongest accommodative drive did not differ chromatically across conditions.
• Second, accommodation is most strongly driven by high-contrast foveal/luminance cues; peripheral contributions exist but are weaker and decline with eccentricity. Consequently, color manipulations located mainly outside the fovea are expected to have a limited effect on accommodation accuracy per se (Barkan et al., 2018).
• Third, any TCA (transverse chromatic aberration) induced by the parafoveal color layout would primarily shift colored images laterally in the periphery (typically on the order of fractions of an arcminute near the fovea and increasing linearly with eccentricity), which degrades peripheral image quality but is not expected to substantially bias foveally driven accommodative accuracy (Winter et al., 2016; Jaeken et al., 2011).
• Fourth, consistent with the considerations above, our ANOVA showed at most a marginal main effect of Color that did not survive Holm correction; no pairwise differences between color conditions reached significance (see the first paragraph of section 3.1). This pattern suggests that, under our stimuli and measurement system, color-dependent LCA was a minor contributor relative to the luminance/contrast manipulations that were central to our hypotheses.

Barkan, Y., & Spitzer, H. (2018). Neuronal mechanism for compensation of longitudinal chromatic aberration-derived algorithm. Frontiers in bioengineering and biotechnology, 6, 12.

Winter, S., Sabesan, R., Tiruveedhula, P., Privitera, C., Unsbo, P., Lundström, L., & Roorda, A. (2016). Transverse chromatic aberration across the visual field of the human eye. Journal of Vision, 16(14), 9-9.

Jaeken, B., Lundström, L., & Artal, P. (2011). Peripheral aberrations in the human eye for different wavelengths: off-axis chromatic aberration. Journal of the Optical Society of America A, 28(9), 1871-1879.

Nevertheless, we have included a mention of this aspect of chromatic aberration in the Discussion section (see last paragraph of section 4.1, lines 452–466).

6) Finally and importantly, the results (see Table 1) are basically that there is no effect of any of their manipulations except that higher luminance leads to smaller pupils and this is widely known already. The largest difference in accommodative lag (as they defined it) is 0.06 diopters which is much smaller than the accuracy of the autorefractor and much smaller than the depth of focus of the human eye.

We appreciate this observation. We acknowledge that the initial explanation of how accommodative responses were recorded (and consequently how accommodative lag was computed) was not sufficiently clear, which may have contributed to some of the concerns raised. In the revised version, we have clarified this methodological aspect.

We believe that the relevance of our findings does not lie in the absolute difference between the maximum and minimum lag values across conditions (e.g., 0.70 ± 0.36 D. for the “Low Contrast (Photopic Condition), yellow non-bright stimulus” vs. 0.64 ± 0.43 D. for the “High Contrast (Mesopic Condition), yellow bright stimulus”, a difference of 0.06 D.), but rather the values ​​of the accommodative lag across the eight experimental conditions. Under normal foveal viewing and pupil sizes of approximately 3–4 mm (as in our participants), the depth of focus of the human eye typically ranges between ±0.20 and ±0.50 D. The fact that the lag values in our study exceeded these average limits supports the idea that the experimental manipulations influenced accommodative stability, and that these deviations could have relative clinical relevance (at least we believe it is important that it was experimentally controlled). Regarding the precision of the instrument for accommodative measurement, it is 0.01 D.

Finally, we emphasize that the ANOVA results revealed significant main effects and interactions consistent with the experimental manipulations, which, in our view, further supports that the observed changes are not random noise but systematic responses to the manipulated visual conditions.

Reviewer 3 Report

Comments and Suggestions for Authors

This experimental study investigates how brightness illusions and ambient light levels (photopic vs. mesopic) affect ocular accommodation, pupillary responses, perceived brightness, and visual comfort. Thirty-two healthy young adults viewed four types of visual stimuli (yellow/blue × bright/non-bright) under two ambient contrast conditions, while accommodative and pupillary responses were recorded using an open-field autorefractor. Subjective ratings of brightness and comfort were also obtained.

2. Strengths
- Novel research focus: The study fills a gap by exploring how brightness illusions affect accommodation.
- Well-structured factorial design (2×2×2): robust and allows for interaction analysis.
- Comprehensive outcome measures: Includes both objective and subjective data.
- Sound statistical methods: Repeated-measures ANOVA with Holm–Bonferroni correction.
- Practical relevance: Findings relate to screen use and visual ergonomics.

3. Major Weaknesses & Suggestions for Revision
A. Pupil response interpretation lacks clarity:
- The absence of significant effects on pupil size is insufficiently explained.
- Suggest explicitly stating that brightness illusion salience may have been too weak.
- A pre-validation of illusion strength is missing and should be acknowledged as a limitation.

B. Short duration limits fatigu relevance:
- 60-second exposures may not simulate digital eye strain adequately.
- Recommend noting this as a limitation and proposing longer tasks in future work.

C. Color interpretation is underdeveloped:
- Discussion on ipRGC and chromatic pupillometry is minimal.
- Expand color physiology rationale and add recent literature.

D. Generalizability is limited:
- Only healthy young adults included.
- Recommend future work on clinical populations (e.g., myopes, presbyopes).

4. Minor Revisions
- Reduce repetitive wording (e.g., 'visual comfort').
- Add explanations to raincloud plots in figure legends.
- Include recent studies on ipRGC and brightness.
- Consider ethical registration details, even for non-clinical studies.

 

Author Response

This experimental study investigates how brightness illusions and ambient light levels (photopic vs. mesopic) affect ocular accommodation, pupillary responses, perceived brightness, and visual comfort. Thirty-two healthy young adults viewed four types of visual stimuli (yellow/blue × bright/non-bright) under two ambient contrast conditions, while accommodative and pupillary responses were recorded using an open-field autorefractor. Subjective ratings of brightness and comfort were also obtained.

2. Strengths

- Novel research focus: The study fills a gap by exploring how brightness illusions affect accommodation.

- Well-structured factorial design (2×2×2): robust and allows for interaction analysis.

- Comprehensive outcome measures: Includes both objective and subjective data.

- Sound statistical methods: Repeated-measures ANOVA with Holm–Bonferroni correction.

- Practical relevance: Findings relate to screen use and visual ergonomics.

3. Major Weaknesses & Suggestions for Revision
4. Pupil response interpretation lacks clarity:

- The absence of significant effects on pupil size is insufficiently explained.

- Suggest explicitly stating that brightness illusion salience may have been too weak.

- A pre-validation of illusion strength is missing and should be acknowledged as a limitation.

We sincerely appreciate your comments and the time you devoted to reviewing our manuscript

We agree that the explanation regarding the absence of significant effects on pupil size deserves greater clarity, especially given that our stimuli were inspired by previous studies reporting clear pupillary responses. We have updated the Discussion section to reflect that, although our illusions were based on Suzuki and colleagues, the salience of our brightness illusion may not have reached the critical threshold required to engage the mechanisms that modulate pupil diameter, discussing the possible reasons for the absence of these effects (see end of the second paragraph of section 4.2, lines 500–507).

Regarding the lack of prior validation of the illusion’s intensity, while it is correct that we did not perform an independent pre-validation of the perceptual strength of the illusion before data collection, a subjective brightness perception measure was included within the experimental protocol itself, immediately following the physiological recordings. The results showed clear and statistically significant differences between stimuli with and without the illusion, confirming that the manipulation was likely effective at the perceptual level. As demonstrated by Suzuki et al. (2019), pupillary constrictions associated with brightness illusions closely correlate with participants’ subjective glare judgments. Consequently, applying a subjective measure as a prior validation could have influenced subsequent physiological responses: explicitly revealing the nature of the illusion would increase perceptual awareness of the experimental manipulation, potentially biasing both the magnitude of the pupillary response and accommodative stability. For this reason, we opted to record subjective ratings within the experimental design rather than as a preliminary step. We consider this approach preserves the ecological validity of the physiological responses and avoids the influence of expectations or attentional biases. Nonetheless, we acknowledge that independent validation in a separate sample of participants could have provided additional information on the perceptual salience of the stimuli, and we propose this approach as a methodological improvement for future studies (see second paragraph of section 4.5, lines 620–623).

1. Short duration limits fatigue relevance:

- 60-second exposures may not simulate digital eye strain adequately.

- Recommend noting this as a limitation and proposing longer tasks in future work.

We acknowledge that the relatively short exposure times in our experiment (60 seconds per condition) are unlikely to induce eye strain. This limitation was already noted in the first version of the manuscript (see first paragraph of Section 4.5) and has now been expanded to emphasize that the short task duration constrains the extrapolation of our findings to contexts of digital eye strain. Accordingly, we suggest that future studies employ longer viewing tasks, closer to real-world screen exposure times, to more realistically assess cumulative effects on accommodation, pupillary response, and visual comfort (see last sentence of the first paragraph of section 4.5, lines 611–614).

1. Color interpretation is underdeveloped:

- Discussion on ipRGC and chromatic pupillometry is minimal.

- Expand color physiology rationale and add recent literature.

We thank the reviewer for their comments. We would like to point out that the last paragraph of section 4.2 (lines 508–533) addresses the interpretation of color, including aspects related to ipRGCs and chromatic pupillometry, and incorporates relevant literature (four of the five references are from 2022).

1. Generalizability is limited:

- Only healthy young adults included.

We would like to note that these aspects are explained in the last paragraph of section 4.5 (lines 639–650).

- Recommend future work on clinical populations (e.g., myopes, presbyopes).

Done (see line 647).

4. Minor Revisions)

- Reduce repetitive wording (e.g., 'visual comfort').

We thank the reviewer for the suggestion. To reduce redundancy, we have opted to use abbreviations throughout the text instead of repeatedly writing certain terms, such as “visual comfort” (VC, in the revised manuscript) and “Perceived Brightness” (PB, in the revised manuscript).

- Add explanations to raincloud plots in figure legends.

Thank you for the suggestion. This has been implemented in Figures 3, 4, and 5.

We have also improved the legend of Figure 6 for better clarity."

- Include recent studies on ipRGC and brightness.

Thank you for the suggestion. Please see last paragraph of section 4.2 (lines 508-533), which addresses these aspects.

- Consider ethical registration details, even for non-clinical studies.

This aspect is included in the last paragraph of section 2.1 (lines 123–125), as well as in the “Institutional Review Board Statement” section (lines 676–678).

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

I appreciate that the authors have attempted to address the negative comments I made concerning the original submission. But I still recommend that this not be published because the motivation for the study is weak and the findings are basically negative.

One point they make in the reply is puzzling. In response to comment #5, they say "an achromatic cross (was) placed at the very center of each stimulus....and was the element intended to drive the accommodative response". But if that's the driver of accommodation, why did they present the various manipulations of the brightness illusion in the periphery? And why did they think that peripheral stimulus would affect accommodation?

Author Response

I appreciate that the authors have attempted to address the negative comments I made concerning the original submission. But I still recommend that this not be published because the motivation for the study is weak and the findings are basically negative.

We sincerely thank the reviewer for the time and effort dedicated to the evaluation of our work, as well as for the constructive comments provided. We understand the concern expressed regarding the perceived weakness of the study motivation and the negative nature of some of the findings.

Nevertheless, we would like to respectfully clarify that our results do show significant effects and interactions, particularly regarding the accommodative system, as well as in the perception of brightness and visual comfort. We believe these contributions are relevant, as they add novel evidence to a scarcely explored domain.

At the same time, we agree that some of our results could be considered "negative" or null, especially in the case of pupillary responses. However, we consider that this type of outcome can also be valuable for the scientific community, since they contribute to a more balanced view of the evidence in the field. Negative or divergent findings are essential for future systematic reviews and meta-analyses, and they reflect the natural variability and complexity of psychophysiological responses. In recent times, the scientific community has increasingly recognized the negative consequences of publication bias toward positive results and has begun to take measures to prevent it. Indeed, increased transparency in research methods and data sharing are helping to create a more complete and accurate scientific picture. These initiatives are driving a more robust way of acquiring knowledge by reducing biased representation of evidence.

In fact, it is not uncommon in science that similar studies within the same area yield non-convergent results. This does not diminish their scientific value, but rather highlights the importance of replication and the identification of potential boundary conditions. In our case, the lack of replication of some previous pupillary effects is openly discussed in the manuscript, where we also outline possible methodological limitations and propose specific directions for future research. For these reasons, we respectfully maintain that the present study provides both positive and negative evidence that can enrich the cumulative knowledge in this area and stimulate further empirical and theoretical advances

One point they make in the reply is puzzling. In response to comment #5, they say "an achromatic cross (was) placed at the very center of each stimulus....and was the element intended to drive the accommodative response". But if that's the driver of accommodation, why did they present the various manipulations of the brightness illusion in the periphery? And why did they think that peripheral stimulus would affect accommodation?

We thank the reviewer for raising this important clarification. Our hypothesis was that the brightness illusion could alter perceptual appearance and thereby modulate visual responses, including pupil size, as has been shown in previous studies using similar stimuli (e.g., Laeng & Endestad, 2012; Suzuki, Minami, Laeng & Nakauchi, 2019). Notably, these studies demonstrated that manipulations of brightness and color can elicit differential pupillary responses (see lines 54–56). In line with these findings, we reasoned that accommodation—given its close functional coupling with the pupillary system (see lines 46–47; lines 76–78)—might also be susceptible to such contextual modulation. This synergy, together with the scarcity of prior research addressing accommodative responses (see lines 57–65) in this context, motivated our study.

     With respect to the role of the central fixation cross, the 2 mm achromatic element was included primarily to secure stable fixation and gaze alignment at the center of the stimulus. While this foveal cross likely provided a consistent accommodative reference, we do not assume it was the sole or exclusive driver of accommodation in our paradigm. To avoid potential ambiguity, we have clarified the wording in lines 199-201 and 461–463 of the manuscript to better reflect this point.

In summary, the fixation cross primarily served as a control element to maintain stable fixation and ensure comparable central stimulation across conditions, whereas the illusion-inducing patterns—better characterized as parafoveal rather than peripheral, given that the 98-mm stimulus size encompasses the foveola, fovea and parafovea, though not the far periphery (see the revised manuscript, lines 210–221 and ** note below)—represented the true experimental manipulation. These parafoveal patterns were intended to shape the visual context surrounding fixation, rather than to replace the foveal accommodative drive per se. Crucially, because the accommodative and pupillary systems operate in close synergy, the established influence of brightness illusions on pupil size provided a strong rationale to test whether similar contextual effects could also extend to accommodation under the same stimulus conditions. In this revised version of the manuscript, we have expanded the information related to these aspects (lines 461–470).

 

 

** Note:

1) Central cross (2 mm)

• Visual angle (diameter): 0.229° (≈0.23°).
• Angular radius (half): 0.115°.
• Retinal radius: ≈0.0340 mm (34 µm).
• Retinal area stimulated: umbo (fovea pit)

2) Bright central white circle (42 mm)

• Visual angle (diameter): 4.810° (≈4.81°).
• Angular radius: 2.405°.
• Retinal radius: ≈0.7136 mm.
• Retinal area stimulated: Foveola + fovea

3) Total stimulus (98 mm)

• Visual angle (diameter): 11.194° (≈11.19°).
• Angular radius: 5.597°.
• Retinal radius: ≈1.661 mm.
• Retinal area stimulated: Foveola + Fovea + Parafovea

Author Response File: Author Response.pdf