'Seeing' proximal representations: Testing attitudes to the relationship between vision and images.

Corrections applied by the visual system, like size constancy, provide us with a coherent and stable perspective from ever-changing retinal images. In the present experiment we investigated how willing adults are to examine their own vision as if it were an uncorrected 2D image, much like a photograph. We showed adult participants two lines on a wall, both of which were the same length but one was closer to the participant and hence appeared visually longer. Despite the instruction to base their judgements on appearance specifically, approximately half of the participants judged the lines to appear the same. When they took a photo of the lines and were asked how long they appeared in the image their responses shifted; now the closer line appeared longer. However, when they were asked again about their own view they reverted to their original response. These results suggest that many adults are resistant to imagining their own vision as if it were a flat image. We also place these results within the context of recent views on visual perspective-taking.

1. Introduction

Corrections applied to sensory input by the visual system, such as size constancy, ensure that the retinal image we receive is encoded in a manner that allows us not to be ‘fooled’ into thinking that a man far away is somehow smaller than a child who is nearby. The distinction between the perception of ‘flat plane’ retinal image features and perception of an object’s ‘real’ physical features was explicit in Rock’s theory of perception [1]. Here, these were referred to as proximal mode and constancy mode and the distinction was seen as particularly important within developmental psychology [2]. Following the early work of Holway and Boring [3], the standard paradigm required observers to judge the size of different stimuli (usually discs), that were placed at different distances from the viewer, and compare these with a sample stimulus. Based on results from this paradigm, Shallo and Rock [4] put forward what Granrud and Schmechel [2] later called the proximal mode sensitivity hypothesis. This suggested that infant perception is more influenced by proximal features than adults. According to Shallo and Rock, as age increases perception is “based on the increased disregard or suppression of proximal mode”.

There are however occasions where adult observers need to rely on the retinal size of objects, such as when a visual artist draws a display that faithfully represents what is seen [5]. Here, more distant objects need to be rendered relatively small. Nevertheless, artists also demonstrate difficulty in accessing proximal vision. Perdreau and Cavanagh [6] showed non-artists, art students, and professional artists two cylinders on a computer screen, one presented against a flat background and one in a 3D ‘hallway’ which gave the illusion of this cylinder being located at a different distance. Their task was to adjust the size of the cylinder in the hallway until the participant judged that it matched the size of the other in terms of their proximal representations. They were told to imagine they were using their fingers to judge the sizes of the items. Results showed that participants consistently overestimated the size of the cylinder presented in the 3D space and moreover that this effect was similar for all groups [for review see 5, see also 7]. Results like these suggest difficulty in or resistance to treating vision (one’s own or another’s) as a ‘flat’ image, even with training in representing perception veridically.

In the present experiment we examined whether adults are open to interrogating their own vision in terms of the proximal rather than distal representation. Rather than use a matching-to-standard paradigm, which requires participants to balance the interference effect of distance and size, we investigated whether participants could ‘see’ the proximal representation of two objects which were already (and explicitly) of equal size but simply located at different distances. This procedure came with the additional benefit that it eliminated the use of 2D depictions of 3D spaces employed in computer-based tasks. In the task, participants stood in a fixed location to the left of two lines that were on the wall of a lab. Fig 1 shows a photo of the lines taken from this location. The lines were the same length but owing to the participant’s location the further line would appear shorter in an uncorrected image of their perspective. In the first phase of the experiment we told participants the following: “Both lines are the same length. However, how long does each line actually appear from your visual perspective? Please answer SAME or DIFFERENT.” When participants responded ‘Different’, we then asked participants which line appeared longer. Note that the framing of the question was designed to ensure that participants had to consider their answer in the context of something beyond their own knowledge of the real length of the stimuli. This was made clear by the ‘however’ following the initial statement of fact. In this way we could examine whether participants would be able and/or willing to access the proximal rather than the distal representation.

Fig 1

A photo of the lines on the wall from the participant’s location in the room.

The two lines were of equal length but the closer line appeared longer. Note that the photograph is a faithful representation of the lines, i.e. we measured the lines in the photo and found that they corresponded to the real visual angle.

Previous research has suggested that training in visual arts offers no significant benefit in the ability to ‘see’ retinal images [5,6]. We wanted to check whether participants who initially failed to access the proximal representation would be more likely to do so after being shown what such an image could look like. To do so we added two further phases to the task. In Phase 2 we gave the participant a camera and instructed them to take a digital photo of the lines from where they stood. We then asked them the same question about the lengths of the lines but this time based on their appearance in the image. Since the image would clearly depict the closer line as longer (as per Fig 1) we predicted that participants would also judge the same. In Phase 3, we removed the camera and photo and then repeated the question from Phase 1. The photograph will have highlighted the length of the lines in a 2D image, and so those participants who did not judge the closer line to look longer in Phase 1 should now correct their responses and do so in Phase 3.

2. Method

We recruited 58 participants from the University of Essex participant pool, each of whom received course credit. Ethical approval was obtained from the University of Essex Ethics Committee Informed consent was recorded in written form and witnessed by the experimenter. Eligibility requirements were normal/correct-to-normal vision and an age between 18–35 (M = 19 years, range 18–24, eight men). Participants stood in a 26cm2 square marked on the floor facing a wall 39cm in front of them, but with their head turned to the right so that they could see two lines, each 32cm in length (3cm height), separated by 64 cm. The closest point of the closest line was 32cm from the area of wall in front of the participants. The experimenter stood in the middle of the room. She told the participants that the lines they were looking at were the same length. She then asked them three questions in a fixed sequence (see Table 1).

Table 1

Scripted instructions to participants.

Phase.	Instruction
1	Both lines are the same length. However, how long does each line actually appear from your visual perspective? Please answer SAME or DIFFERENT. [If DIFFERENT: Which appears longer?].
2 (Photo)	How long does each line appear in the photo you just took? Please answer SAME or DIFFERENT. [If DIFFERENT: Which appears longer?].
3	Now please look at the two lines on the wall once more. How long does each line appear from your perspective? Please answer SAME or DIFFERENT. [If DIFFERENT: Which appears longer?].

In Phase 1, we asked them how long the lines actually appeared from their visual perspective, with a fixed-choice answer of either SAME or DIFFERENT, the latter being followed up with an extra question about which. If adults can take their own perspective in a visual sense as a result of this appearance question, then more participants should respond that the closest line appeared longer than the converse. In Phase 2 we gave the participant a hand-held digital camera and asked them to take a picture of the two lines from the same location. We then asked them to view the digital photograph they had taken and judge how long the lines appeared in it, using the same question/response structure as before. For Phase 3 the experimenter took back the camera. The participant was then instructed to look at the lines on the wall again, and they were asked the first question once more. Given that everyone had now witnessed a pictorial representation of their own visual perspective in the previous condition, any participants who had not said that the closest line appeared longer in Phase 1 should now be more likely to do so in Phase 3.

3. Results

The results are displayed in Table 2.

Table 2

Results.

	Same (%)	Closest line longer (%)	Furthest line longer (%)
Phase 1	53	47	0
Phase 2	0	100	0
Phase 3	48	50	2

Phase 1

We ran a Chi-Square test on the first question concerning whether the lines appeared the same length or different length, with the null hypothesis that each be selected 50% of the time. Overall, 31 judged them the same and 27 judged them different, a contrast that was not significant, chi square (1, 58) = 0.276, p = .599. However, all 27 participants who responded ‘different’ judged the closest line to appear longer. Given the absence of any responses favouring the further line as longer, no statistical comparison could be conducted. In sum, approximately half of participants judged the lines to look the same and half judged the closer line to be longer.

Phase 2

All participants said the closest line appeared longer in the photograph. No statistical analyses were conducted since all responses were the same.

Phase 3

We used the same analysis as for Phase 1. Despite having seen the photograph in Phase 2, results patterned as in Phase 1. Precisely the same number of participants responded ‘same’ as ‘different’ (29 each), chi square (1, 58) = 1, p = 1. Of the 29 who judged them different, 28 responded that the closest line looked longer and only one said the furthest line looked longer, a difference that was significant, chi square (1, 29) = 25.138, p < .001.

Effect of photo on judgements based on vision

To assess whether seeing the photograph in Phase 2 influenced responses in Phase 3, we dummy coded responses as 0 for ‘Closest line longer, 1 for ‘Same’ and 2 for ‘Furthest line longer’. We then ran a Friedman’s ANOVA by ranks on all the data. The test found a significant difference in the distribution of responses across the three phases, chi square (2, 58) = 53.118, p < .001. Follow-up pairwise comparisons using the Bonferroni correction revealed that more ‘closest line longer’ responses were made based on the photo (Phase 2) than for both Phase 1 (adj. p < .001) and Phase 3 (adj. p < .001). Crucially, there was no difference in the frequency of these responses between Phase 1 and 3 (adj. p = 1). At the individual level, of the 31 participants who gave ‘same’ responses in Phase 1, 84% (n = 26) also gave ‘same’ responses in Phase 3. Five switched from ‘same’ responses to ‘closer line longer’ in Phase 3, two switched in the opposite direction, and one switched from ‘closer line longer’ to ‘further line longer.’ In sum, seeing the photo in Phase 2 had no significant impact on how participants responded on Phase 3 relative to Phase 1.

4. Discussion

The results showed that while about half of participants judged the closer line as being longer, suggesting they did access and use the proximal representation, half did not. However, when basing their judgements on a photo of the lines every participant judged the closer line to look longer in a photo they took. Surprisingly, in Phase 3 the vast majority who initially judged the lines to appear the same reverted back to their original response despite having just declared the closer line to appear longer in the photo. This suggests that even when participants are made explicitly aware of what a 2D image of their vision might look like they treated actual sensory input differently. This perseverance suggests considerable resistance to seeing proximal representations of vision.

How do we account for these findings? These results are explicable in terms of what is sometimes called naïve or folk optics, namely folk theories about how vision works. Such beliefs can vary widely from person to person, and lead to very different and often inaccurate responses to the same problems [8,9]. This is nicely exemplified by the Venus Effect, whereby an observer sees an agent and a mirror and believes that the agent sees their reflection in the mirror as the observer does, despite the agent and mirror not being along the observer’s line of sight [9,10, see also 11]. Importantly for the present experiment, these naïve theories can be inconsistent not only with accepted science but even people’s own declarative knowledge [8]. This offers an explanation for why participants proved resistant to changing their responses even after viewing the photograph.

The present work also speaks to the issue of visual perspective taking. A number of people have begun to argue that when humans assume another agent’s perspective the representation on which this alternative viewpoint is based is depictive or ’quasi perceptual’ [12,13]. Cole and Millett [14], and Cole, Millett [15] have however challenged this claim on theoretical grounds, and in a visual perspective-taking study based on the same stimuli as the present experiment adults also failed to judge that line closer to another agent would appear shorter [16]. A depictive representation must, at the very least, code for the relative distances between different points in a scene [17], as seen by the other agent. The present work does not however support the depictive account of perspective taking. Humans seem to be poor at considering even their own perspectives in this way, let alone other people’s.

Overall, the results of the present study suggest that while some people are open to interrogating their vision in terms of proximal representations about the same number of people not only have difficulty doing so but also demonstrate considerable resistance to change even after witnessing what such a representation might look like. It remains an open question as to precisely why this should be difficult. One explanation is that people are resistant to the principle that vision can be equated to a flat image. According to this view, the reason that those participants who failed to judge the closer line longer is not because they could not access a proximal representation but because the logic of the question itself was rejected, as ‘corrected’ vision is the only type of vision they could reasonably conceive of. This implies that adults are disinclined to entertain vision in as a proximal image, even when the context is favourable to such behaviour. However, it does not mean that they are necessarily unable to do so.

There is a related but more procedural explanation for the present data that we must consider. Since at least 1960s [18], size constancy researchers have long known that participant interpretation of task requirements is particularly important. Shebilske and Peters [19], for instance, wrote that “the manipulation of instructions is a potent source of variance in constancy experiments. This variance can be attributed to the information given or implied by a particular set of instructions”. Our method for circumventing this possibility was to present participants with a photograph (in Phase 2) of their own viewpoint and ensure that responses were close to ceiling. In this Phase all participants demonstrated that they could understand and work from a 2D representation of their viewpoint. Thus, while some responses from Phase 1 might be explicable in terms of a misunderstanding of the instruction to judge appearance, by Phase 3 this becomes less plausible.

Another possibility is that those participants who did not judge the closer line to appear longer in Phase 3 may have simply wanted to be consistent in their response when presented with the same question as they had in Phase 1. By this account, our results are not explicable in terms of a disinclination to entertain a proximal image but rather a disinclination to appear inconsistent in an experimental setting. We cannot rule this possibility out, but note that such an account leaves unexplained the fact that by responding differently in Phase 2 and Phase 3 participants also rejected the possibility that their vision corresponded to the photograph, which is itself an external and 2D representation of their own vision. A consistency account would thus be more viable if participants maintained the same response that they made in Phase 1 across the rest of the task, including the photograph. Instead, it appears that a disinclination to entertain proximal images provides a better account for our findings.

In sum, these results demonstrate the resistance adults have to entertaining proximal representations of vision. Overall, these results concur with other research, both theoretical and empirical, suggesting that adults do not tend to entertain vision in terms of truly ‘depictive’ imagery [5,14,15].

(XLSX)

Click here for additional data file.

30 Jun 2021

PONE-D-21-09371

Can we see our proximal representations?

PLOS ONE

Dear Dr. Samuel,

Thank you for submitting your manuscript to PLOS ONE, and apologies for the slight delay in the review process - this was, in no small part, due to me being on parental leave. In the meantime, your submission has been assessed by two expert reviewers, and you will see that they are both broadly positive about the research question and the quality of the manuscript itself. However, they both present some very useful constructive criticism of the report that would need to be addressed if this were to be published in the journal.

Some of these points pertain to strengthening the write-up itself, with regards to a firmer grounding in the relevant literature and a clearer delineation of some methodological detail. However, the more substantive issue is the requirement for more data - this is something that both reviewers request, and I also concur. One reviewer sees this in terms of the generality of the effect, in the absence of overt manipulation of relevant factors, and the other in terms of how participants interpret the task itself. Both issues are very pertinent, and would usually be relatively simple to address. That said, we are currently in a very atypical situation, and this is one of those paradigms that fundamentally requires face-to-face testing. Still, I do think that it would be appropriate to follow-up on this helpful reviewer feedback, and perhaps it will become more straightforward to do so as the world begins to find its feet again.

I am, therefore, pleased to invite you to submit a revised version of the manuscript that addresses the points raised during the review process. I do realise that the thought of collecting more data may be disheartening at the moment, but I hope that you appreciate the reasoning here, and I'm confident that it would make for a much better paper if you were able to respond to the commentary you have received.

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Reviewer #1: This paper presents a study of size constancy. Participants were asked to access their own vision as if it were an uncorrected 2D image. Approximately half of the participants judged the objects to appear the same, supporting a strong constancy effect. The authors conclude that many adults not only have difficulty interrogating their own perception as if it were a flat image but also show resistance to change.

The topic is interesting, indeed classic, and the analysis is sound. The first problem is that the paper fail to properly acknowledge the large literature and the many studies that already exist. In the introduction it says "relatively few studies have examined the degree to which humans can interrogate their own vision". This is too strong.

A quick list of relevant studies

- Irv Rock used the term "proximal mode" and studied it extensively, including in his book on shape and slant.

- There is work with infants about whether they see the same object at different distances as different objects (e.g., Slater, A., Mattock, A., & Brown, E. (1990). Size constancy at birth: Newborn infants' responses to retinal and real size. Journal of experimental child psychology, 49(2), 314-322)

- Some of the work on mirrors is cited but maybe the most relevant paper is: Lawson, R., Bertamini, M., & Liu, D. (2007). Overestimation of the projected size of objects on the surface of mirrors and windows. Journal of Experimental Psychology: Human Perception and Performance, 33(5), 1027)

The second problem with the paper is the problem we always have with single study papers. That is, what about generality. In this case the problem is even more serious as not only we have a single study, but the design of the study is also minimal. No manipulation of physical size, distance, or angle.

In summary, there are limitations at the moment but on the other hand both of these problems can be addressed. With respect to the literature, more discussing of older papers and rewriting is possible. With respect to the single study, the procedure is simple and it would be easy and informative to replicate and extend the study.

Reviewer #2: The present study tests whether people can access an uncorrected, 2-dimensional representation of their vision (proximal representation), much like a photograph. They show that people perform at chance when judging whether two horizontal lines of equal length appeared to be the same or different lengths from their perspective (where the closer line would appear visually longer in an uncorrected 2D image). Despite all participants then correctly judging a photograph of the lines, they still performed at chance when repeating the first task again. The authors conclude that many people find it difficult to visualise proximal representations, even when presented with an example of how it would look.

I found this manuscript interesting to read and the findings have relevance for the naïve optics literature. The manuscript is well-presented and clearly-written, the methods are clearly described, the data has been made available and the analyses seem appropriate. Unfortunately, however, I have concerns about whether the methodology of the experiment captures exactly what the authors are trying to test. I have particular concerns about how participants were asked to judge the lines and I am not convinced that the task instructions are a) clear enough to be interpreted correctly by participants and b) whether the task can be completed by means other than accessing proximal representations. I therefore recommend major revisions for this manuscript. I would be satisfied if the authors collect more data that convinces me that 1) people do indeed understand the task, 2) the results remain the same, and 3) that the data truly reflects the ability to access proximal representations and cannot be explained by any other means such as access to knowledge.

Major issues:

1. Task instruction

In the task, participants are told: “Both lines are the same length. However, how long does each line actually appear from your visual perspective?”. The authors note that saying “however” encouraged participants to challenge their own knowledge and base responses on proximal representations.

Unfortunately, despite the justification for how the question is framed, I am not convinced that all participants would be able to fully understand what is required of them in this task. It is not clear to me how asking how something “appears” is in reference to how it would look as a flat image. Of course, it is clear in the manuscript that having participants inspect a photo of the lines should indeed clear up any confusion for when they are asked a second time, but I still fail to see how a naive participant would understand the relevance of the photo for the task. This might explain why participants perform at chance and do not change their answers when asked again.

Additionally, by already stating that the lines are of equal length, it sounds like a trick question, and asking participants to repeat the same task again so soon after could result in a general reluctance to change their answer rather than a “resistance to see proximal representations”.

One suggestion would be to instead ask participants a more direct question that really taps into a 2D representation of vision, such as “if you draw the lines as you see them from your perspective, which would you draw longer” or even “if you took a photo…” – this would also make it clear why taking the photo was relevant .

2. Visual representation or knowledge?

The experiment is designed to test whether people have access to a 2-dimensional visual representation of what they can see, however the question can be answered simply by accessing knowledge about size constancy, that closer objects are visually bigger than farther objects, without having to conjure up this image per se. Therefore, even if the participants do understand the question, they do not need to access proximal representations to answer it.

Minor comments:

1. On page 5, line 101, the authors refer to Figure 2 which is not present in the manuscript.

2. In the results for Phase 3 on page 7, line 143-144, the authors incorrectly state that “…the same number of participants responded “same” as “different” (29 each)”. The data actually shows that 28 responded “same” and 30 responded “different”.

3. It would be helpful if the authors could make it clear whether the height of the participant was measured and whether these differences in visual angle would influence how much longer the closer line would “appear” compared to the further line.

4. It would also be helpful if the authors could give more details about how they instructed participants to take the photo – i.e. did they hold the camera exactly where their eyes were or was it held out in front? Did the experimenter inspect the photos that were taken to ensure they were a true depiction of the participant’s perspective?

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Reviewer #1: No

Reviewer #2: No

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14 Jul 2021

PONE-D-21-09371

Can we see our proximal representations?

PLOS ONE

Dear Dr. Samuel,

Thank you for submitting your manuscript to PLOS ONE, and apologies for the slight delay in the review process - this was, in no small part, due to me being on parental leave. In the meantime, your submission has been assessed by two expert reviewers, and you will see that they are both broadly positive about the research question and the quality of the manuscript itself. However, they both present some very useful constructive criticism of the report that would need to be addressed if this were to be published in the journal.

Some of these points pertain to strengthening the write-up itself, with regards to a firmer grounding in the relevant literature and a clearer delineation of some methodological detail. However, the more substantive issue is the requirement for more data - this is something that both reviewers request, and I also concur. One reviewer sees this in terms of the generality of the effect, in the absence of overt manipulation of relevant factors, and the other in terms of how participants interpret the task itself. Both issues are very pertinent, and would usually be relatively simple to address. That said, we are currently in a very atypical situation, and this is one of those paradigms that fundamentally requires face-to-face testing. Still, I do think that it would be appropriate to follow-up on this helpful reviewer feedback, and perhaps it will become more straightforward to do so as the world begins to find its feet again.

I am, therefore, pleased to invite you to submit a revised version of the manuscript that addresses the points raised during the review process. I do realise that the thought of collecting more data may be disheartening at the moment, but I hope that you appreciate the reasoning here, and I'm confident that it would make for a much better paper if you were able to respond to the commentary you have received.

Authors general reply:

We are grateful to the Editor and Reviewer for their time and consideration of our manuscript. In the revised document we have highlighted sections where text has been added or edited, for convenience. An overarching theme of our revision concerns the primary research question. In short, we needed to be clearer that we were investigating inclination/propensity rather than ability when it comes to accessing proximal images. It is clear that adults are able to interrogate what they see in such a way that they can develop a reasonably accurate flat-mage version of it. No data is required to prove this point – the fact that still life drawing/painting exists does this job perfectly. Instead, we were more interested in adults’ willingness (or otherwise) to entertain vision in proximal terms. The photo manipulation also makes more sense (we believe) when this point is made more clearly, because the fact that it made no difference to the final, third Phase demonstrates that participants were unmoved: they would not equate their vision to a flat image, even under experimental conditions. As a result, our main approach to our revision has been to ensure that our work is much more clearly situated within this question of willingness/disinclination. We have thus changed the title to reflect this, and removed references to whether adults ‘can’ access proximal imagery, as this word allows the interpretation as ‘ability’ rather than ‘propensity’.

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

Reviewer #1: This paper presents a study of size constancy. Participants were asked to access their own vision as if it were an uncorrected 2D image. Approximately half of the participants judged the objects to appear the same, supporting a strong constancy effect. The authors conclude that many adults not only have difficulty interrogating their own perception as if it were a flat image but also show resistance to change.

The topic is interesting, indeed classic, and the analysis is sound. The first problem is that the paper fail to properly acknowledge the large literature and the many studies that already exist. In the introduction it says "relatively few studies have examined the degree to which humans can interrogate their own vision". This is too strong.

A quick list of relevant studies

- Irv Rock used the term "proximal mode" and studied it extensively, including in his book on shape and slant.

- There is work with infants about whether they see the same object at different distances as different objects (e.g., Slater, A., Mattock, A., & Brown, E. (1990). Size constancy at birth: Newborn infants' responses to retinal and real size. Journal of experimental child psychology, 49(2), 314-322)

- Some of the work on mirrors is cited but maybe the most relevant paper is: Lawson, R., Bertamini, M., & Liu, D. (2007). Overestimation of the projected size of objects on the surface of mirrors and windows. Journal of Experimental Psychology: Human Perception and Performance, 33(5), 1027)

The second problem with the paper is the problem we always have with single study papers. That is, what about generality. In this case the problem is even more serious as not only we have a single study, but the design of the study is also minimal. No manipulation of physical size, distance, or angle.

Authors reply:

Although we only have one experiment (and thus acknowledge that generality is limited) what is very striking about the results is how huge the effect is. Across the three phases, responses go from chance to ceiling and back to chance. This suggests we are dealing with a basic principle – humans can determine proximal size (Phase 2) but not when they have to introspect their own immediate experience.

Our study was designed to investigate the tendency (or otherwise) to treat image in terms of proximal representations. We used size constancy as a tool to this end, but please note that the experiment is not a ‘study of size constancy’. Seen this way, the principal characteristic the lines needed to have was to appear different in a proximal image. Phase 2 (the photograph) makes clear that this was the case. If the study had been about size constancy itself, then we agree that it would be useful to manipulate physical aspects of the stimuli.

We have revised the Introduction to reflect the Reviewer’s (very correct) comment regarding developmental research. We have also added the Lawson et al. 92017) reference as suggested in the section on mirrors.

In summary, there are limitations at the moment but on the other hand both of these problems can be addressed. With respect to the literature, more discussing of older papers and rewriting is possible. With respect to the single study, the procedure is simple and it would be easy and informative to replicate and extend the study.

Authors reply:

If it was not for Covid we would certainly have replicated the procedure and extended the work. Given the current rules on testing at Essex and Plymouth, we are not however able to begin this before October at best. It’s not therefore that easy. Given what we said in the previous point about the effect being huge we have opted not to extend the work yet. However, we have added to and amended sections of the Introduction and (more importantly) a large segment of the discussion to explain why we feel that the current data speak quite clearly to the notion of adults’ disinclination to entertain their vision in terms of proximal imagery.

Reviewer #2: The present study tests whether people can access an uncorrected, 2-dimensional representation of their vision (proximal representation), much like a photograph. They show that people perform at chance when judging whether two horizontal lines of equal length appeared to be the same or different lengths from their perspective (where the closer line would appear visually longer in an uncorrected 2D image). Despite all participants then correctly judging a photograph of the lines, they still performed at chance when repeating the first task again. The authors conclude that many people find it difficult to visualise proximal representations, even when presented with an example of how it would look.

I found this manuscript interesting to read and the findings have relevance for the naïve optics literature. The manuscript is well-presented and clearly-written, the methods are clearly described, the data has been made available and the analyses seem appropriate. Unfortunately, however, I have concerns about whether the methodology of the experiment captures exactly what the authors are trying to test. I have particular concerns about how participants were asked to judge the lines and I am not convinced that the task instructions are a) clear enough to be interpreted correctly by participants and b) whether the task can be completed by means other than accessing proximal representations. I therefore recommend major revisions for this manuscript. I would be satisfied if the authors collect more data that convinces me that 1) people do indeed understand the task, 2) the results remain the same, and 3) that the data truly reflects the ability to access proximal representations and cannot be explained by any other means such as access to knowledge.

Major issues:

1. Task instruction

In the task, participants are told: “Both lines are the same length. However, how long does each line actually appear from your visual perspective?”. The authors note that saying “however” encouraged participants to challenge their own knowledge and base responses on proximal representations.

Unfortunately, despite the justification for how the question is framed, I am not convinced that all participants would be able to fully understand what is required of them in this task. It is not clear to me how asking how something “appears” is in reference to how it would look as a flat image. Of course, it is clear in the manuscript that having participants inspect a photo of the lines should indeed clear up any confusion for when they are asked a second time, but I still fail to see how a naive participant would understand the relevance of the photo for the task. This might explain why participants perform at chance and do not change their answers when asked again.

Additionally, by already stating that the lines are of equal length, it sounds like a trick question, and asking participants to repeat the same task again so soon after could result in a general reluctance to change their answer rather than a “resistance to see proximal representations”.

One suggestion would be to instead ask participants a more direct question that really taps into a 2D representation of vision, such as “if you draw the lines as you see them from your perspective, which would you draw longer” or even “if you took a photo…” – this would also make it clear why taking the photo was relevant .

Authors reply:

We can see that participants might not want to give a different response (on Phase 3) to what they gave just before (on Phase 1) once they fully understand what is being asked of them (after they see the photo). We now discuss this alternative explanation in our revised Discussion. In that section we point out that while the logic of the counterargument is sound insofar as it relates to potential consistency between Phases 1 and 3, the contrast with responses in Phase 2 (the photograph) weakens the explanatory power of this alternative (please see lines 206-227). In relation to the possibility of drawing lines in response to the question, we had considered this (we used this method in our perspective-taking paper on which this paradigm was based), but opted against any method that might allow participants to adopt a strategy whereby they could effectively line their response up with their vision (as a painter holds a brush up in front of their eyes to judge lengths, or a photographer makes a frame with their fingers, etc), as this would be contrary to the spirit of the task as one of mental representation rather than physical action.

2. Visual representation or knowledge?

The experiment is designed to test whether people have access to a 2-dimensional visual representation of what they can see, however the question can be answered simply by accessing knowledge about size constancy, that closer objects are visually bigger than farther objects, without having to conjure up this image per se. Therefore, even if the participants do understand the question, they do not need to access proximal representations to answer it.

Authors reply:

We are in complete agreement here. In fact, we came to this work via our own previous work on visual perspective taking. An opinion is developing which states that VPT is based on a pictorial representation. For this to be true, an observer should be able to determine the relative distance between different points in a display as seen from another individual (i.e., when the observer is attempting to take that person’s perspective). We therefore wanted to know whether an observer can do this with respect to their own proximal vision, let alone someone else’s. We have made the ‘knowledge not pictorial imagery’ point in a number of previous papers (e.g., Cole, Samuel, Millett, & Eacott, 2020). It’s even in the title of Millett, D’Souza, and Cole (2019). However, we note (there as well as here) that geometric reasoning like this is either not applied or applied incorrectly, because as our results show accuracy was at chance.

Minor comments:

1. On page 5, line 101, the authors refer to Figure 2 which is not present in the manuscript.

Authors reply:

We thank the Reviewer for their comments. We have made the relevant correction in the manuscript.

2. In the results for Phase 3 on page 7, line 143-144, the authors incorrectly state that “…the same number of participants responded “same” as “different” (29 each)”. The data actually shows that 28 responded “same” and 30 responded “different”.

Authors reply:

The figures and analysis are correct: 29 responded ‘Same’ and 29 ‘Different’. However, the confusion probably arises because one of the ‘Different’ responders said the further line appear longer, thus 28 gave ‘closer line longer’ and 30 did not.

3. It would be helpful if the authors could make it clear whether the height of the participant was measured and whether these differences in visual angle would influence how much longer the closer line would “appear” compared to the further line.

Authors reply:

We did not measure participants’ height. However, variation in line length would be vanishingly small given the way the lines were arranged from where the participant stood (Figure 1 is a photo taken from precisely that location and the difference is very clear, as all participants verified in Phase 2).

4. It would also be helpful if the authors could give more details about how they instructed participants to take the photo – i.e. did they hold the camera exactly where their eyes were or was it held out in front? Did the experimenter inspect the photos that were taken to ensure they were a true depiction of the participant’s perspective?

Authors reply:

Participants took a photo by looking at the screen on the digital camera, meaning they had to hold the camera in front of their eyes when capturing the image (in the natural manner). The photos themselves were not assessed by the experimenter (indeed, this could have introduced perspective-taking), but given that they saw the participant take the photo and, more importantly, that they showed 100% uniformity in their response based on the photo, we have no concerns.

Submitted filename: Reply To Reviewers.docx

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26 Jul 2021

PONE-D-21-09371R1

‘Seeing’ proximal representations: Testing attitudes to the relationship between vision and images.

PLOS ONE

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Reviewer #2: All comments have been addressed

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Reviewer #2: Yes

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Reviewer #1: If we were not in a pandemic I would have insisted on a second study. But I take the point about how hard it is to collect data and therefore I agree that this study can be published on its own.

I only have a final comment.

In their reply the authors note that "the experiment is not a study of size constancy", and they also say "we were investigating inclination/propensity rather than ability"

Ok, that is an important point. But in the abstract I read "we investigated whether adults can treat their own vision as if it were an uncorrected 2D image". The word CAN in particular implies that this is a study of the ABILITY to access 2D information despite size constancy. So some more changes to the words is necessary, other readers will read this and conclude that this is a study of size constancy.

Reviewer #2: My initial concerns about this work were (1) whether the task instructions were clear enough for participants to follow as intended, (2) whether the results could be explained by general reluctance to change their answers, rather than a “resistance to see proximal representations”, and (3) whether the task could be completed by accessing knowledge about size constancy, rather than accessing proximal representations.

While my initial request was to collect more data to resolve these issues, the authors have instead provided a comprehensive discussion of these issues in the manuscript, highlighting the limitations they create for this work. I am satisfied with the revisions made to this manuscript.

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27 Jul 2021

Reviewer 1:

In their reply the authors note that "the experiment is not a study of size constancy", and they also say "we were investigating inclination/propensity rather than ability"

Ok, that is an important point. But in the abstract I read "we investigated whether adults can treat their own vision as if it were an uncorrected 2D image". The word CAN in particular implies that this is a study of the ABILITY to access 2D information despite size constancy. So some more changes to the words is necessary, other readers will read this and conclude that this is a study of size constancy.

Reply:

We agree that the use of 'can' is too ambiguous. We have changed this line in the abstract to read as follows:

In the present experiment we investigated how willing adults are to examine their own vision as if it were an uncorrected 2D image, much like a photograph.

Submitted filename: Reply To Reviewers R2.docx

Click here for additional data file.

12 Aug 2021

‘Seeing’ proximal representations: Testing attitudes to the relationship between vision and images.

PONE-D-21-09371R2

Dear Dr. Samuel,

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PLOS ONE

Additional Editor Comments:

Thanks for your response to the recent review, and I am satisfied that the change in abstract wording improves and clarifies the nature of the study for the reader.

Reviewers' comments:

13 Aug 2021

PONE-D-21-09371R2

‘Seeing’ proximal representations: Testing attitudes to the relationship between vision and images.

Dear Dr. Samuel:

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