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Question for the botanists and entomologists - polarised images

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#1 JMC

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Posted 14 April 2019 - 08:18

Woke up this morning and wondered "do bees (and other insects) see polarised light?", specifically is their vision polarised. Yes, this happens occasionally, waking up wondering stuff. The reason being was the cross polarised images of flowers I took a couple of months back, where in the UVA region at least, cross polarisation, made the pollen stand out really well against the rest of the flower. The original post is here;

http://www.ultraviol...dpost__p__26164

A quick google search revealed a few papers mentioning about bees being able to navigate using polarised light.

This got me thinking. For those trying to emulate insect vision, should they be using polarised light (or are they doing this already)?

Perhaps this is already well known, I'm not an entomologist or botanist, but thought I would put it out there as a question, as it's not something I've seen discussed before.

#2 Cadmium

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Posted 14 April 2019 - 08:35

You know... there is a place in Colorado that makes UV polarizers?

#3 Andrea B.

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Posted 14 April 2019 - 16:57

Keep in mind that a reflected UV photo does not represent bee/insect vision.

The closest we can come to representing a kind of bee vision *might* be by using a UV+B+G filter or some kind of stacking technique. But that does not really represent bee/insect vision either because there is no way to portray reflected UV either singly or in combination with reflected blue or green.

So with either a reflected UV photo or a UV+B+G photo, I would say that using a polarizer is not going to get you very much closer to any kind of true bee/insect vision. But, then, improving details is always nice so why not use one?

..........

Did you know that some authors think that while bees can receive 3 signal types (UV, B, G), those signals may not necessarily be combined into a trichromatic image? Another reason why our attempts at emulating bee vision fall short.
It is kind of difficult to imagine this kind of vision. For example suppose humans could receive R,G,B but only G and B were brain-combined into an image. We would see the world in hues of blue, cyan, green and maybe a small amount of slightly yellowish green, but we could still detect reflected red/orange. Perhaps we would interpret the red/orange signal as “Fire/Hot/Danger”, who knows.
Andrea G. Blum
Often found hanging out with flowers & bees.

#4 Cadmium

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Posted 14 April 2019 - 22:40

here is the UV polarizer place I mentioned:
http://boldervision....arizers/bvo-uv/

#5 DaveO

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Posted 15 April 2019 - 06:10

Andrea,

From our favourite bee-man Adrian Horridge:

WHAT DOES THE HONEYBEE SEE? AND HOW DO WE KNOW? A CRITIQUE OF SCIENTIFIC REASON
ADRIAN HORRIDGE

Polarisation
In the bee, electron microscopy shows that the microvilli of four of the retinula cells lie at right angles to the others in cross-sections, from which von Frisch et al. (1960) inferred that they detect the polarisation plane of the blue sky as part of the sun compass. This caused a lot of confusion because two directions of microvilli were not sufficient to detect all directions of polarisation without ambiguity. Opinions differ about whether the rhabdom is twisted as a specialisation to prevent the colour vision being disturbed by polarisation of light that has been reflected at natural surfaces. The ommatidium is not twisted when carefully frozen before being fixed for sectioning. Electrophysiology shows that retinula cells of normal ommatidia are indeed sensitive to the plane of polarisation and that the polarisation sensitivity of single receptors is confounded with spectral sensitivity. The ninth (basal) retinula cell is also a puzzle. Detection of the compass direction from the main axes of the polarisation pattern of the blue of the sky is done by specialised ommatidia along the dorsal edge of the eye, where the spatial resolution is poor but the microvilli are oriented in the pattern of a preset filter that matches the polarisation pattern around the position of the sun. By rotating itself, the bee receives a maximum or minimum stimulus from the sky (see Chapter 8).

Other authors have said that as the bee can perceive the polarisation of UV light in the sky (by the sky pointing ommatidia in the bee eye) it helps with navigation to and from the food source.

Dave

#6 Andrea B.

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Posted 15 April 2019 - 17:05

Thanks, Dave, for finding this and posting.
I figured Horridge would have some observation about polarization,
but I hadn't had time to return to this topic.


By rotating itself, the bee receives a maximum or minimum stimulus from the sky (see Chapter 8).

I was particularly wondering about whether a bee could perform some kind of rotation maneuver.
So there it is!
Usually when we see them foraging around flowers, they are just making short hop flights.
I wonder if I patiently sat in the garden and tried to see a bee approaching from afar, whether
any kind of rotation could be observed? It's probably too subtle, but who knows?

Returning to JMC's original thoughts and my response,
Horridge's observations about bees & polarization indicates that we might as well
add a polarizer when attempting to emulate bee/insect vision
even though we will never fully capture the way a bee actually "sees". :D
Andrea G. Blum
Often found hanging out with flowers & bees.

#7 JMC

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Posted 15 April 2019 - 18:38

Interesting, and thanks for sharing the paper ref. I had read that they detected polarisation in the sky, which got me thinking about whether polarisation when viewing the flower was useful for them. It does now make me wonder whether flowers which do not rely on insect pollenisation, have pollen which is less easy to 'see' with polarised UV light (i.e. a smaller difference between non-polarised and cross polarised appearance at a relevent set of wavelengths).