<p>I think part of what makes this question confusing is the use of expressions like "what the eye sees", "what the brain sees" and "what the frog's eye tells the frog's brain". Nobody sees anything except the experiencing subject. When one stops thinking that the brain (or some visual-system part of the brain) observes the image on the retina, then the question of whether anything is being flipped becomes meaningless. </p>

<p>As regards perceptual adaptation, it is interesting to note that it is not universal. In Sperry's famous frog-eye-inversion experiment, the frogs never adapted.</p>

<p><strong>References</strong></p>

<ul>
<li>Roger W. Sperry (1943). Effect of 180 Degree Rotation of the Retinal Field on Visuomotor Coordination. <em>The Journal of Experimental Zoology</em> 92 (3): 263–279</li>
</ul>

CC BY-SA 3.0
2012-02-18T17:24:55.067Z
2012-02-18T17:24:55.067Z
Peter Helfer
<p>The fact that the image does not <em>appears</em> upside-down has to do with the way visual information is processed in the brain. In his book, Jeff Hawkins argues that the low-level visual features on the retina (being upside down, distorted, and changing rapidly) are lost in the process of forming invariant representation. And it's those representations that we experience consciously.</p>

<p>From On Intelligence (<a href="http://www.onintelligence.org/" rel="noreferrer">official site</a>, <a href="http://blog.mohammadzadeh.info/media/blogs/snf/Resources/HTM/OWL%20Books%20-%20On%20Intelligence.pdf?mtime=1296774047" rel="noreferrer">pdf</a>)</p>

<blockquote>
  <p>The light receptors in your retina are unevenly distributed. They are
  densely concentrated in the fovea at the center, and get gradually
  sparser out in the periphery. In contrast, the cells in the cortex are
  evenly distributed. The result is that the retinal image relayed onto
  the primary visual area, V1, is highly distorted [<em>and upside-down, if you will</em>]. When your eyes
  fixate on the nose of a face versus on an eye of the same face, the
  visual input is very different, as though it is being viewed through a
  distorting fisheye lens that is jerking violently to and fro. Yet when
  you see the face, it doesn't appear distorted, and it doesn't appear
  to be jumping around. Most of the time you aren't even aware that the
  retinal pattern has changed at all, let alone so dramatically. You
  just see "face." (Figure 2b shows this effect on a view of a beach
  landscape.) This is a restatement of the mystery of invariant
  representation we talked about in chapter 4, on memory. What you
  "perceive" is not what V1 sees. How does your brain ever know it is
  looking at the same face, and why don't you know the inputs are
  changing and distorted?</p>
</blockquote>

<p><img src="https://i.sstatic.net/6ZAnn.png" alt="figure 2a 2b"></p>

<p><em>The process of forming invariant representations is explained in the book, but I won't quote it there because its quite long.</em></p>

CC BY-SA 3.0
2012-10-14T14:11:51.523Z
2012-10-14T14:11:51.523Z
Benjamin Crouzier
<p>There are many transformations between the light hitting your retina and your perception of the world.</p>

<p>The signals from your retina initially travel through the <a href="https://myweb.rollins.edu/jsiry/VisualPathways.jpg" rel="nofollow">visual pathways</a> to reach your visual cortex, where visual information is processed. The representation of this visual information in your brain is also <a href="http://www.cell.com/neuron/fulltext/S0896-6273(07)00376-5" rel="nofollow">shaped by other brain activity</a> representing <a href="https://en.wikipedia.org/wiki/Multisensory_integration#General_introduction" rel="nofollow">your other senses</a> (sound, touch, etc) and also internal processes like your current <a href="http://www.ncbi.nlm.nih.gov/pubmed/9375191" rel="nofollow">mood</a> or <a href="https://www.researchgate.net/profile/Tobias_Egner/publication/26776567_Expectation_(and_attention)_in_visual_cognition/links/0912f50bb5013cf9dd000000.pdf" rel="nofollow">expectations</a>.</p>

<p>By the time all of this information is incorporated into your conscious perception, the orientation of the photons as they hit your retina is gone and all you have is your brain's interpretation of the world around you.</p>

CC BY-SA 3.0
2016-04-18T21:17:27.643Z
2016-04-18T21:24:04.157Z
2016-04-18T21:24:04.157Z
K A
<p>It is <strong>not the case that the brain flips the retinal image</strong>, <strong>nor does it have to</strong>, <strong>nor are there any images in the brain like there are on the retina</strong>. It is <strong>just as meaningless to say that the retinal image is upside down in relation to the orientation of our perceptions</strong>.</p>

<p>Richard L. Gregory gives a nice explanation:</p>

<blockquote>
  <p>It is generally accepted that this does not need a special compensation mechanism because retinal images are not seen, as objects are seen […]. A compensating mechanism is not needed as they are not objects of perception but rather one stage of processing lying between objects and vision. […] When the head is tilted, the world remains upright. This extends to standing on one's head, when the retinal image is reversed and yet up and down remain normal. (Richard L. Gregory (2004): Illusions, In: The Oxford Companion to the Mind, 2nd Edition, p. 429).</p>
</blockquote>

<p>Another way to grasp this issue is by the difference of physical space and phenomenal space, as Norbert Bischof does:</p>

<blockquote>
  <p>We thus have to distinguish a <em>physical space</em>, in which our body is located and the brain processes take place, and a <em>space experience</em> which the phenomenal world is embedded in. [… Both] <em>cannot be localized</em> in relation to one another. There is no superordinate coordinate system which they can be jointly fit into. They are […] »incommensurable«, which literally means there is no common scale that could be applied to both. […] (Norbert Bischof (2009): Psychologie, 2nd Edition, pp. 48–49, my translation).</p>
</blockquote>

<p>Bischof goes on to state that the retinal image and the consciously experienced phenomenon can not possibly be integrated within one and the same space in the first place, and thus don't stand in any spatial relation whatsoever.</p>

CC BY-SA 3.0
2016-04-18T21:14:59.023Z
2016-04-26T09:42:01.293Z
2016-04-26T09:42:01.293Z
huh
<p>It is not meaningful to talk about your brain processing something as 'right-side up&quot;' or 'upside-down'. The 'images' in your brain are just collections of neural activations, and not actual pictures. Thus they cannot have an orientation. The only meaningful way to test your question is to try flipping the input the brain receives and seeing if it can cope.</p>
<p>Fortunately, the brain <strong>is</strong> capable of flipping your visual field if required as measured through <a href="http://en.wikipedia.org/wiki/Perceptual_adaptation" rel="noreferrer">perceptual adaptation</a> experiments using inversion glasses. This has been demonstrated very drastically in studies, by for instance requiring a participant to wear inversion glasses for a long time. At first they are confused, and unable to orient themselves and do basic tasks, however after enough time the brain can adopt enough to even do activities like riding a bike. This suggests that from the only way you can measure things (i.e. behaviorally) the brain is capable of adapting to an upside down world (some participants even reported that after extended use the world even seemed &quot;right side up&quot;). This is functionally equivalent to the brain being able to process your visual information in either orientation. If it is capable of processing in either orientation, the question of &quot;does my brain flip the image&quot; becomes a pseudo-question and unanswerable.</p>
<h3>References</h3>
<ul>
<li><p>Taylor, J. G. (1962). The behavioral basis of perception. New Haven: Yale University Pres</p>
</li>
<li><p>Harris, C.S. (1965) &quot;Perceptual adaptation to inverted, reversed, and displaced vision.&quot; Psychological Review 72(6): 419-444. [<a href="https://netfiles.uiuc.edu/wang18/www/psych334/readings/harris1965.pdf" rel="noreferrer">pdf</a>]]</p>
</li>
<li><p>Di Paolo, E.A. (2003) &quot;Organismically-inspired robotics: homeostatic adaptation and teleology beyond the closed sensorimotor loop&quot;, {Dynamical systems approach to embodiment and sociality: 19-42 [<a href="http://liris.cnrs.fr/enaction/docs/documents2006/dipaolo-hart.pdf" rel="noreferrer">pdf</a></p>
</li>
</ul>

CC BY-SA 3.0
2016-09-29T06:29:27.687Z
Nice answer.I'm not an expert but i'd like to share a personal experience attached to this, I'm myopic with cylindrical power,when I started wearing specs, in those days, I felt as if my height had increased and it was very difficult for me to make the adjustments, my steps used to falter, later on, I believe my eye-brain co-ordination have made reasonable progress, I don't have that issue anymore. http://physics.stackexchange.com/q/228077. Why can't we say that the new born baby see the world very differently, `Babies learn to see over a period of time, much like they learn to walk and talk.`
yeppe
CC BY-SA 3.0
2016-11-27T10:01:50.863Z
Reminds me of a lyric in "Clint Eastwood" by Gorillaz - "Y'all can see me now 'cause you don't see with your eye. You perceive with your mind".
Matt
CC BY-SA 3.0
2012-02-09T00:40:29.440Z
As in my comment, I know about this study. In informal discussions it is most often used as a proof your brain 'does' flip images. As you state, I never understood the reasoning behind this, and your answer confirms my suspicion it is just an urban myth.
Steven Jeuris
CC BY-SA 3.0
2012-02-09T00:51:17.600Z
Thanks for the paper! _"Spatial relations are not originally perceived by the eye, but are the result of the association of visual sensations with previous muscular and tactual experiences."_ _"This belief in the primacy of touch **is so ingrained** that experimental results are sometimes flagrantly misinterpreted in order to support it."_ .... _Finally_ I have a conversation stopper! Such a fun feeling when your intuition turns out to be right. :)
Steven Jeuris
CC BY-SA 3.0
2012-02-09T00:35:17.823Z
2012-02-09T00:56:07.640Z
2020-06-17T09:55:31.633Z
Artem Kaznatcheev
<p><a href="http://www.newscientist.com/blog/lastword/2008/05/eye-level.html" rel="noreferrer">The following</a> is a common scientific statement, which you don't have to google long for to find:</p>

<blockquote>
  <p>The eye views images upside-down in the manner of a camera lens, but
  our brains reinterpret this input to allow us to see things the
  correct way up.</p>
</blockquote>

<p><img src="https://i.sstatic.net/8EDa8.gif" alt="enter image description here"></p>

<p>My first question is quite straightforward: <strong>Is this statement valid?</strong></p>

<p>I don't understand why you should come to the conclusion that your brain should 'flip' the image. Wouldn't your brain be able to cope just fine without flipping it? If anything I would suspect the brain to <em>not</em> flip the image, if there is no reason to do so.</p>

<p>In order for this statement to be valid, I would expect a scientific theory/experiment from which can be concluded that the brain does process the vision in such a way that, after it being processed all subsequent processing occurs on the 'inverted' image. That seems to me to be the most logical interpretation of 'to flip'.</p>

CC BY-SA 3.0
2012-02-09T00:21:53.173Z
I wanted to keep the question short and concise, but as a sidenote, I do know about the experiment where a person wears glasses which inverts their vision after which their vision adapts to it. But this only proves your vision is _able_ to adapt to what you are used to. It doesn't prove that your brain inverts the image initially.
Steven Jeuris
CC BY-SA 3.0
2012-02-09T00:27:49.283Z
how would you ever hope to tell apart if the brain flips the image or works with it upside down? It is obvious that the projection on your retina is upside down... but there is functionally no difference between 'right'-side up and 'upside'-down in processing... except for your subjective experience.
Artem Kaznatcheev
CC BY-SA 3.0
2012-02-12T06:12:32.303Z
I think it is NOT a valid statement, precisely because it is a meaningless question. If I ask you to tell me whether 1 / 0 = 'something', you can without a doubt say no it doesn't equal 'something', because 1 / 0 doesn't equal anything.
Phillip Cloud
CC BY-SA 3.0
2012-02-15T19:38:17.213Z
What it means by "flipping it" is just that it interprets the image received correctly, by understanding that it is presented upside down. The final image that your brain processes matches with your tactile input which interprets everything as right way up.
Schroedingers Cat
CC BY-SA 3.0
2012-02-15T19:51:39.733Z
@SchroedingersCat: But it's exactly this reasoning I address. From the paper referenced in [Artem's answer](http://cogsci.stackexchange.com/a/339/21): _"Spatial relations are not originally perceived by the eye, but are the result of the association of visual sensations with previous muscular and tactual experiences."_ As far as I understand it doesn't make any sense to state "flipping", or "receiving correctly", or that your tactile input does interpret it the right way up. You only know about "the correct way up" by associationg vision with tactile input.
Steven Jeuris
CC BY-SA 3.0
2012-02-15T21:00:45.770Z
The point I was trying to make is that it is upside down wrt your tactile input. There is a need to align the two, so that your tactile associations can be related to your visual ones. It is just about relating the various stimuli appropriately.
Schroedingers Cat
CC BY-SA 3.0
2015-01-05T12:18:50.340Z
@Tomp24 Welcome to Stack exchange and thank you for sharing your thoughts! However, 'upside down' is a subjective percept; it is constructed by and with respect to the viewer. The world cannot be upside down 'in reality'. The world is. And we perceive it.
AliceD
CC BY-SA 3.0
2016-04-18T23:06:46.780Z
Also of interest: http://cogsci.stackexchange.com/questions/1125/where-is-the-visual-image-that-we-see-finally-assembled
Arnon Weinberg
CC BY-SA 3.0
2016-12-19T15:14:34.713Z
There is no [up or down only neurons firing on shapes](http://biology.stackexchange.com/questions/1614/how-do-we-know-the-brain-flips-images-projected-on-the-retina-back-around#answer-2664)... So it might as well be following... https://i.sstatic.net/xJXd6.png
Matas Vaitkevicius
CC BY-SA 4.0
2018-09-23T01:35:13.607Z
What does it mean to flip? We know that a pair of lens can flip the image. And might not, depends on focal distance. It's said that if our eyes were lens then they would flip the image. But I thought this makes no sense: with only lens instead of eyes I would be blind. It is brain who decides where is top and where is bottom.
rus9384
CC BY-SA 4.0
2018-09-23T09:53:33.730Z
As I stated in the question, @rus9384, my interpretation of 'to flip' would be that _"the brain does process the vision in such a way that, after it being processed all subsequent processing occurs on the 'inverted' image"_. But, as pointed out by the answers, it is not meaningful thinking about 'brain processing' like that.
Steven Jeuris
<neuroscience><vision><theoretical-neuroscience><philosophy-of-mind>
Why would the brain flip the images perceived by your eyes?
Steven Jeuris
# Why would the brain flip the images perceived by your eyes?

(Asked by: username_0 on 2012-02-09)

[The following](http://www.newscientist.com/blog/lastword/2008/05/eye-level.html) is a common scientific statement, which you don't have to google long for to find:

> The eye views images upside-down in the manner of a camera lens, but
> our brains reinterpret this input to allow us to see things the
> correct way up.

![enter image description here](https://i.sstatic.net/8EDa8.gif)

My first question is quite straightforward: **Is this statement valid?**

I don't understand why you should come to the conclusion that your brain should 'flip' the image. Wouldn't your brain be able to cope just fine without flipping it? If anything I would suspect the brain to *not* flip the image, if there is no reason to do so.

In order for this statement to be valid, I would expect a scientific theory/experiment from which can be concluded that the brain does process the vision in such a way that, after it being processed all subsequent processing occurs on the 'inverted' image. That seems to me to be the most logical interpretation of 'to flip'.

**Tags:** neuroscience, vision, theoretical-neuroscience, philosophy-of-mind

> **Comments:**
> **username_0**: I wanted to keep the question short and concise, but as a sidenote, I do know about the experiment where a person wears glasses which inverts their vision after which their vision adapts to it. But this only proves your vision is _able_ to adapt to what you are used to. It doesn't prove that your brain inverts the image initially.  
> **username_1**: how would you ever hope to tell apart if the brain flips the image or works with it upside down? It is obvious that the projection on your retina is upside down... but there is functionally no difference between 'right'-side up and 'upside'-down in processing... except for your subjective experience.  
> **username_2**: I think it is NOT a valid statement, precisely because it is a meaningless question. If I ask you to tell me whether 1 / 0 = 'something', you can without a doubt say no it doesn't equal 'something', because 1 / 0 doesn't equal anything.  
> **username_3**: What it means by "flipping it" is just that it interprets the image received correctly, by understanding that it is presented upside down. The final image that your brain processes matches with your tactile input which interprets everything as right way up.  
> **username_0**: @SchroedingersCat: But it's exactly this reasoning I address. From the paper referenced in [Artem's answer](http://cogsci.stackexchange.com/a/339/21): _"Spatial relations are not originally perceived by the eye, but are the result of the association of visual sensations with previous muscular and tactual experiences."_ As far as I understand it doesn't make any sense to state "flipping", or "receiving correctly", or that your tactile input does interpret it the right way up. You only know about "the correct way up" by associationg vision with tactile input.  
> **username_3**: The point I was trying to make is that it is upside down wrt your tactile input. There is a need to align the two, so that your tactile associations can be related to your visual ones. It is just about relating the various stimuli appropriately.  
> **username_4**: @Tomp24 Welcome to Stack exchange and thank you for sharing your thoughts! However, 'upside down' is a subjective percept; it is constructed by and with respect to the viewer. The world cannot be upside down 'in reality'. The world is. And we perceive it.  
> **username_5**: Also of interest: http://cogsci.stackexchange.com/questions/1125/where-is-the-visual-image-that-we-see-finally-assembled  
> **username_6**: There is no [up or down only neurons firing on shapes](http://biology.stackexchange.com/questions/1614/how-do-we-know-the-brain-flips-images-projected-on-the-retina-back-around#answer-2664)... So it might as well be following... https://i.sstatic.net/xJXd6.png  
> **username_7**: What does it mean to flip? We know that a pair of lens can flip the image. And might not, depends on focal distance. It's said that if our eyes were lens then they would flip the image. But I thought this makes no sense: with only lens instead of eyes I would be blind. It is brain who decides where is top and where is bottom.  
> **username_0**: As I stated in the question, @username_7, my interpretation of 'to flip' would be that _"the brain does process the vision in such a way that, after it being processed all subsequent processing occurs on the 'inverted' image"_. But, as pointed out by the answers, it is not meaningful thinking about 'brain processing' like that.  

---

## 5 answers

### Answer by username_1 on 2012-02-09. Score: 47 | Accepted answer

It is not meaningful to talk about your brain processing something as 'right-side up"' or 'upside-down'. The 'images' in your brain are just collections of neural activations, and not actual pictures. Thus they cannot have an orientation. The only meaningful way to test your question is to try flipping the input the brain receives and seeing if it can cope.

Fortunately, the brain **is** capable of flipping your visual field if required as measured through [perceptual adaptation](http://en.wikipedia.org/wiki/Perceptual_adaptation) experiments using inversion glasses. This has been demonstrated very drastically in studies, by for instance requiring a participant to wear inversion glasses for a long time. At first they are confused, and unable to orient themselves and do basic tasks, however after enough time the brain can adopt enough to even do activities like riding a bike. This suggests that from the only way you can measure things (i.e. behaviorally) the brain is capable of adapting to an upside down world (some participants even reported that after extended use the world even seemed "right side up"). This is functionally equivalent to the brain being able to process your visual information in either orientation. If it is capable of processing in either orientation, the question of "does my brain flip the image" becomes a pseudo-question and unanswerable.

### References

* Taylor, J. G. (1962). The behavioral basis of perception. New Haven: Yale University Pres
* Harris, C.S. (1965) "Perceptual adaptation to inverted, reversed, and displaced vision." Psychological Review 72(6): 419-444. [[pdf](https://netfiles.uiuc.edu/wang18/www/psych334/readings/harris1965.pdf)]]
* Di Paolo, E.A. (2003) "Organismically-inspired robotics: homeostatic adaptation and teleology beyond the closed sensorimotor loop", {Dynamical systems approach to embodiment and sociality: 19-42 [[pdf](http://liris.cnrs.fr/enaction/docs/documents2006/dipaolo-hart.pdf)

> **Comments:**
> **username_0**: As in my comment, I know about this study. In informal discussions it is most often used as a proof your brain 'does' flip images. As you state, I never understood the reasoning behind this, and your answer confirms my suspicion it is just an urban myth.  
> **username_0**: Thanks for the paper! _"Spatial relations are not originally perceived by the eye, but are the result of the association of visual sensations with previous muscular and tactual experiences."_ _"This belief in the primacy of touch **is so ingrained** that experimental results are sometimes flagrantly misinterpreted in order to support it."_ .... _Finally_ I have a conversation stopper! Such a fun feeling when your intuition turns out to be right. :)  
> **username_12**: Nice answer.I'm not an expert but i'd like to share a personal experience attached to this, I'm myopic with cylindrical power,when I started wearing specs, in those days, I felt as if my height had increased and it was very difficult for me to make the adjustments, my steps used to falter, later on, I believe my eye-brain co-ordination have made reasonable progress, I don't have that issue anymore. http://physics.stackexchange.com/q/228077. Why can't we say that the new born baby see the world very differently, `Babies learn to see over a period of time, much like they learn to walk and talk.`  
> **username_13**: Reminds me of a lyric in "Clint Eastwood" by Gorillaz - "Y'all can see me now 'cause you don't see with your eye. You perceive with your mind".  

---

### Answer by username_8 on 2012-02-18. Score: 20

I think part of what makes this question confusing is the use of expressions like "what the eye sees", "what the brain sees" and "what the frog's eye tells the frog's brain". Nobody sees anything except the experiencing subject. When one stops thinking that the brain (or some visual-system part of the brain) observes the image on the retina, then the question of whether anything is being flipped becomes meaningless.

As regards perceptual adaptation, it is interesting to note that it is not universal. In Sperry's famous frog-eye-inversion experiment, the frogs never adapted.

**References**

* Roger W. Sperry (1943). Effect of 180 Degree Rotation of the Retinal Field on Visuomotor Coordination. *The Journal of Experimental Zoology* 92 (3): 263–279


---

### Answer by username_9 on 2012-10-14. Score: 12

The fact that the image does not *appears* upside-down has to do with the way visual information is processed in the brain. In his book, Jeff Hawkins argues that the low-level visual features on the retina (being upside down, distorted, and changing rapidly) are lost in the process of forming invariant representation. And it's those representations that we experience consciously.

From On Intelligence ([official site](http://www.onintelligence.org/), [pdf](http://blog.mohammadzadeh.info/media/blogs/snf/Resources/HTM/OWL%20Books%20-%20On%20Intelligence.pdf?mtime=1296774047))

> The light receptors in your retina are unevenly distributed. They are
> densely concentrated in the fovea at the center, and get gradually
> sparser out in the periphery. In contrast, the cells in the cortex are
> evenly distributed. The result is that the retinal image relayed onto
> the primary visual area, V1, is highly distorted [*and upside-down, if you will*]. When your eyes
> fixate on the nose of a face versus on an eye of the same face, the
> visual input is very different, as though it is being viewed through a
> distorting fisheye lens that is jerking violently to and fro. Yet when
> you see the face, it doesn't appear distorted, and it doesn't appear
> to be jumping around. Most of the time you aren't even aware that the
> retinal pattern has changed at all, let alone so dramatically. You
> just see "face." (Figure 2b shows this effect on a view of a beach
> landscape.) This is a restatement of the mystery of invariant
> representation we talked about in chapter 4, on memory. What you
> "perceive" is not what V1 sees. How does your brain ever know it is
> looking at the same face, and why don't you know the inputs are
> changing and distorted?

![figure 2a 2b](https://i.sstatic.net/6ZAnn.png)

*The process of forming invariant representations is explained in the book, but I won't quote it there because its quite long.*


---

### Answer by username_10 on 2016-04-18. Score: 3

There are many transformations between the light hitting your retina and your perception of the world.

The signals from your retina initially travel through the [visual pathways](https://myweb.rollins.edu/jsiry/VisualPathways.jpg) to reach your visual cortex, where visual information is processed. The representation of this visual information in your brain is also [shaped by other brain activity](http://www.cell.com/neuron/fulltext/S0896-6273(07)00376-5) representing [your other senses](https://en.wikipedia.org/wiki/Multisensory_integration#General_introduction) (sound, touch, etc) and also internal processes like your current [mood](http://www.ncbi.nlm.nih.gov/pubmed/9375191) or [expectations](https://www.researchgate.net/profile/Tobias_Egner/publication/26776567_Expectation_(and_attention)_in_visual_cognition/links/0912f50bb5013cf9dd000000.pdf).

By the time all of this information is incorporated into your conscious perception, the orientation of the photons as they hit your retina is gone and all you have is your brain's interpretation of the world around you.


---

### Answer by username_11 on 2016-04-18. Score: 2

It is **not the case that the brain flips the retinal image**, **nor does it have to**, **nor are there any images in the brain like there are on the retina**. It is **just as meaningless to say that the retinal image is upside down in relation to the orientation of our perceptions**.

Richard L. Gregory gives a nice explanation:

> It is generally accepted that this does not need a special compensation mechanism because retinal images are not seen, as objects are seen […]. A compensating mechanism is not needed as they are not objects of perception but rather one stage of processing lying between objects and vision. […] When the head is tilted, the world remains upright. This extends to standing on one's head, when the retinal image is reversed and yet up and down remain normal. (Richard L. Gregory (2004): Illusions, In: The Oxford Companion to the Mind, 2nd Edition, p. 429).

Another way to grasp this issue is by the difference of physical space and phenomenal space, as Norbert Bischof does:

> We thus have to distinguish a *physical space*, in which our body is located and the brain processes take place, and a *space experience* which the phenomenal world is embedded in. [… Both] *cannot be localized* in relation to one another. There is no superordinate coordinate system which they can be jointly fit into. They are […] »incommensurable«, which literally means there is no common scale that could be applied to both. […] (Norbert Bischof (2009): Psychologie, 2nd Edition, pp. 48–49, my translation).

Bischof goes on to state that the retinal image and the consciously experienced phenomenon can not possibly be integrated within one and the same space in the first place, and thus don't stand in any spatial relation whatsoever.


---

