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Thread: Perception

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    Arch-Σigmoid Ausphotography Regular ameerat42's Avatar
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    Perception

    Here's a 10-and-a-half-minute video I found in a link somewhere else.
    It's here because it has implications for photography. The first bit was
    (for me) surprising, and the rest may be of interest...

    Now look here...
    CC, Image editing OK.

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    How are your eyes, GZZA?

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    Ausphotography Addict Gazza's Avatar
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    Quote Originally Posted by ameerat42 View Post
    How are your eyes, GZZA?
    Havta re-think what we see/saw
    If you replace the 'W' with 'T' in When, Where and What, you get the answer for each question.
    CC more than welcome. Remember, I can't be offended so go for it. Feel free to post your ideas with an edit if you have time. Thanks in advance.



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    http://steveaxford.smugmug.com/
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    Eyes are very smart (maybe that should be - visual processing is vey smart). My left eye had a blood clot and part of the retina died. If I look at the page of a book with just my left eye, some of the letters or words are completely missing. But, if I look at a tree or a face or most things, I see them perfectly well. My brain just fills in the missing bits.

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    Steve, sorry to hear that. However, we can all only see the blind spot in each eye by tricking the eye/brain system into revealing it ...

    A lot of simple visual processing actually takes place in the bipolar and amacrine cells in the retina before the signals leave via the optic nerves for the optic chiasm and onwards from there to the visual cortex.

    Also, each eye is in fact two half eyes ... The retina is in two halves, and the right and left visual field from each eye are combined with its other half from the other eye in the optic chiasm.

    Retinal tissue is composed of neurons, i.e. brain cells, and the eye and brain have to be considered as a single functional unit in order to understand them.

    Then there is the distinction between wavelength and colour. These are processed by two separate nuclei in the brain. Loss of the colour nucleus leads to complete loss of colour vision. However, loss of the wavelength nucleus causes vision to become bizarre.

    We are complex little beasties!

    BTW, the creature with the best colour vision that we know of so far is the Mantis Shrimp! Squid and Octopi are pretty darn good. Humans and other mammals come a fair way down the list ... .

    @Am - interesting video, mate .

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    Do you mean wavelength and colour or brightness and colour? We pay very little attention to wavelength, even though we pretend to relate it to colour.

    Thanks John. I can still see well enough for photography and it has taught me that what we see ain't necessarily there. It's just our approximation of reality, and that can be nothing like it on occasions.
    Last edited by Steve Axford; 13-02-2017 at 1:29pm.

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    Wavelength and colour, Steve.

    Brightness and the apparent dynamic range of our visual system is a whole other can of worms!

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    How do our eyes see wavelength apart from through our rod cells that are the way we see colour? We only get a very rough idea of wavelength as, for example, a blue and yellow wavelength are indistinguishable from a green wavelength, and a red and a blue wavelength appear the same as a purple wavelength.

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    The two nuclei interpret the wavelength and colour information. They are separate from the visual cortex, and only contain a few hundred neurons each. It appears from brain trauma studies that the interpretation of wavelength takes precedence over that of colour. Loss of the colour nucleus leads to normal perception, but in shades of grey. Loss of the colour nucleus leads to the loss of meaningful vision.

    For something that's so ubiquitously useful, colour doesn't actually exist!
    It is an almost universal property that is a mental construct from the way eyes detect wavelength, and how the brain processes and interprets this info ...

    As an example, what colour is UV? Being one of the 10% or so of humanity who sees into this part of the spectrum, it appears sort of pinkish/mauve to me. An unfortunate consequence of seeing this way, I must wear full UV cut glasses, even at night (HID headlights are pretty painful ... ). If I'm driving a long distance, I wear pink night driving glasses.

    Vision was one of my great interests when I did my degree in psychology (along with a few other subjects ... it's a long story, and a longer degree!). Specifically, how reception becomes perception. The study of visual illusions informs this understanding. It remains a great interest to this day, along with how a piece of wetware (a brain) becomes a conscious, self-aware persona, whether in a human or an ant ...

    Some interesting stuff about the mantis shrimp is here:

    http://theconversation.com/mantis-sh...-but-why-17577

    On reading that article more carefully, much of the information is wrong - e.g. they have six colour receptor chemicals, not 16 ...
    They are still fascinating creatures. The Wikipedia article is more accurate (on yer, Jimmy and friends), here:

    https://en.wikipedia.org/wiki/Mantis..._visual_system
    Last edited by John King; 13-02-2017 at 7:01pm.

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    Quote Originally Posted by John King View Post
    ...An unfortunate consequence of seeing this way, I must ... wear pink night driving glasses...
    Wha-a-a-t?! Forced to wear rose-coloured glasses

    (Ta for the link, too.)

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    LOL, and you're welcome .

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    I too have been fascinated by colour and what you say makes little sense to me. Do you have any references on wavelength and vision? My understanding is that we only have a very vague idea of wavelength. We call it colour, and yes it is a construct, but it serves a very useful purpose.
    Mantid shrimps have lots of colour sensors, but are since we can't ask what they see, we can only guess.

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    Steve, Richard Gregory's "Eye and Brain" used to be a great once-over-lightly, but I haven't looked to see if anything equivalent is currently available. Here:

    http://press.princeton.edu/titles/6141.html

    Interestingly, one of my lecturers in Physiological Psychology was a Dr Michael Wood - probably just a coincidence!

    Knowing the colour receptor chemicals present in the retina of a creature allows analysis of what it is possible for it to see. That research has revealed some fascinating information about this fascinating creature.

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    Awl wright! I'm starting to come up with a formulation now...

    Perception = 10% Reception + 90% Deception +/- Delusional Constant*



    * The Delusional Constant is akin to Einstein's Cosmological Constant, the delusion arising from
    evidence in an article I read today that it is changing.

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    Quote Originally Posted by John King View Post
    Steve, Richard Gregory's "Eye and Brain" used to be a great once-over-lightly, but I haven't looked to see if anything equivalent is currently available. Here:

    http://press.princeton.edu/titles/6141.html

    Interestingly, one of my lecturers in Physiological Psychology was a Dr Michael Wood - probably just a coincidence!

    Knowing the colour receptor chemicals present in the retina of a creature allows analysis of what it is possible for it to see. That research has revealed some fascinating information about this fascinating creature.
    Hi John, There has been a lot of hard science in analysing visual perception in recent years using such tools as PET scans to trace where signals are processed in our brains. But, wavelength is not something that is processed by our brain. I'm not sure how you got this idea.The book you reference has chapters on brightness, movement and colour, not wavelength.

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    Haha.

    Let's not diverge further into Einsteinian physics ... ... or his cosmological constant; or the big bang theory; or the "standard model" ...

    How to mix a Universe:

    1) Take lots of Hydrogen (a Universe full ... )

    2) place Bamix into mixture for no longer than 10 seconds (or 10^-47s, if you prefer ... )

    3) Place in oven to bake for no more than 10 minutes

    4) Ignore all evidence about plasmas, gravity not being a force but the topology of spacetime, 'tired' light, etc

    5) Present Universe as whatever you want it to be

    6) Explain away all inconsistencies by super string theory, multi-verses, inflation, or your choice of astrological happen-stances ...

    7) Shout down non-believers (like engineers, observational astronomers, and their ilk ... )

    Done ...

    At least science is (generally) self-correcting, even if it does take hundreds of years sometimes!

    - - - Updated - - -

    Quote Originally Posted by Steve Axford View Post
    Hi John, There has been a lot of hard science in analysing visual perception in recent years using such tools as PET scans to trace where signals are processed in our brains. But, wavelength is not something that is processed by our brain. I'm not sure how you got this idea.The book you reference has chapters on brightness, movement and colour, not wavelength.
    Steve, a question.

    What stimulates the rods and cones to change the chemical structure of the photoreceptor chemicals in them?
    Is it colour?
    Or is it the specific wavelength of light to which the particular photosensitive chemical responds to?
    I no longer have my old copy of Gregory. Perhaps I should buy a more modern copy rather than relying on my (rapidly deteriorating) memory from nearly 40 years ago ... .

    - - - Updated - - -

    [Edit]

    Steve, the chapter titles in Jimmy Watson's "Molecular Biology of the Gene" don't tend to give anything more than a vague idea of the content either ... .

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    Wavelength certainly has a relationship with rods but they measure what we think of as colour, not really wavelength. 40 years is a long time in the biological sciences, and even more in neuro- psychology.

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    Yes, 40 years is a long time. However, I have maintained my knowledge over that time ...

    Colour is a function of our perception of wavelength, not the other way around.

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    Whoops, I meant cone cells (the ones responsible for colour vision), not rod cells which are responsible for dim light vision. We obviously both need to keep reading. My apologies.

    My point is that we process colour not wavelength. Our cone cells each contain one of 3 photoreceptor pigments that react to light. One reacts most strongly to light with a wavelength of 564–580 nm (red), one 534–545 nm (green), and one 420–440 nm (blue). They do not measure wavelength, but just react most strongly to a that wavelength, but also react to a lesser extent to other wavelengths. Our brain interprets those 3 signals to to represent colour. We do not detect anything like wavelength as it would make no sense. I'll give you an example. Imagine we see a light source that contains 2 wavelengths, one blue (say 450nm) and one yellow (say 570nm). What we see is green. Yet the wavelength is clearly not green. If we were shown light with a single wavelength of 510nm we would also see green. It is worth noting that almost all green birds are really yellow + blue birds.

    The point being that our eyes do not see wavelength. If you ever use a spectrometer, then you will get wavelength information. You will see each component of the light as a separate wavelength and intensity. If we wanted to make a spectrometer, we would not choose the way our eyes are made as we could not get very much useful information on wavelength. On the other hand, when interpreting the real world, wavelength is at best confusing. Colour, even though it is a construct, is much better.

    It occurred to me that maybe the confusion about wavelength comes from what is called colour constancy. This is where we try to keep colours constant in differing circumstances. For example we try to see the same objects as the same colour irrespective of the lighting conditions. This may be an apple which we know is red. If we see it under normal light we will see it as red. If we see it in predominantly green light we will also see it as red, yet when the light from the apple is measured it may be radically different from the red we saw under normal light. Our cone cells should also see it as another colour, but our visual system will adjust the colour depending on the surrounds. Perhaps this is where you got the wavelength confusion from.

    Cameras are a very good analogy for our eyes. They have red, green and blue sensors, just like our cone cells. They also apply a white balance to the scene to adjust for colour constancy factors (not as well as we do, but really very good). Cameras, like eyes, do not measure wavelength. They react to colour.

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    Steve. How does what you say account for "colour blindness"?

    Colour has to be a construct, IMO, to account for that.

    Secondly, for the camera-eye analogy, the concentration of cones and rods (AFAIK) is in the
    fovea.

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