File talk:BirdVisualPigmentAbsorbance.svg

Tetrachromacy

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  File:Cones SMJ2 E.svg (left)
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  File:Tetrachromaticpigments01.png (middle)
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  File:BirdVisualPigmentSensitivity.svg (right)

Hi. Your image to the right says "sensitivity" in its name, but appears to be more a plot of "absorption". Curiously, the one it was made from, center, said it was a plot of absorption, and looks more like spectral sensitivity. I had fixed up a trichromat version (measured resonsivities, left). Now I'm wondering what that source says that you noted on commons; does it have the data? Absorption, or responsivity? Dicklyon (talk) 21:52, 2 July 2009 (UTC)

My error. I assumed that sensitivity was measured as a function of absorption. I am still unclear about the method and whether this really matches in vivo response (nerve potential measurements or some method like that?) Let me look for the source again and check it more carefully. My recollection is that it had the graph, not the method description or data measurements. Thanks for being eagle eyed. Shyamal (talk) 01:05, 3 July 2009 (UTC)

Ok, here is the original image caption

Fig. 1.1 Normalized absorbance of the visual pigments from the four types of single retinal cone cells in the Gouldian finch (Erythrura gouldiae): UV = ultraviolet, SW = shortwave, MW = medium wave, LW = longwave. Curves are the best-fitting visual pigment templates for the average spectra based on microspectrophotometry. For comparison, the wavelengths of maximum spectral sensitivity of the blue, green and red cones of humans are indicated by arrows at the top of the figure. Redrawn and adapted from Hart et al. 2000. Journal of Comparative Physiology,

Series A 186: 681-674

The full reference cited is Hart, N. S., Partridge, J. C., Bennett, A. T. D. and Cuthill, I. C. 2000. Visual pigments, cone oil droplets and ocular media in four species of estrildid finch. Journal of Comparative Physiology, Series A 186: 681-674. Some addition things they say in the adjoining text

Second, the retinas of birds and humans differ in the number and type of light sensitive cones present. Humans possess only three single cone types, which are maximally sensitive to wavelengths of light in the blue, green and red regions of the human visible spectrum (see Fig. 1.1). In contrast, birds possess six cone classes: four types of single cones, and the two dissimilar double cones, which are also found in fish and turtles (Liebman and Granda 1971; Ohtsuka 1985), but are lacking in humans. While the function of the double cones remains unknown (Hart et al. 1998; Wilkie et al. 1998), current evidence suggests that they are not used in color vision (Vorobyev et al. 1998; Vorobyev and Osorio 1998). The avian single cones span the avian-visible spectrum fairly evenly, although there is some variation between species in the wavelengths of maximum sensitivity of their visual pigments. Most birds, including the Passeriformes (and Budgerigar) have a true UV visual pigment, with a maximum sensitivity around 355-380 nm. In contrast, in the Anseriformes, Ciconiiformes, Columbiformes and Galliformes, the UV sensitive cone is replaced with a violet-sensitive cone (lmax 400-426 nm). The reasons for this dichotomy between bird families are unknown at present (Bowmaker et al. 1997; Yokoyama et al. 1998; Yokoyama et al. 2000), but importantly, both the UV and violet sensitive cones allow birds to see in the UV. The three other single cone pigments are more similar in their spectral sensitivity, but not without some variation (Hart et al. 1998): short-wave (lmax 430-463 nm), medium-wave (lmax 497-510 nm) and long-wave (lmax 543-571 nm) sensitive visual pigments. Lastly, in birds, each of the four single cone photoreceptors contains a different type of oil droplet through which light must pass before reaching the visual pigment (for a review see Hart 2001). In all but one of the cone types, the oil droplets contain carotenoid pigments (i.e. short-wavelength absorbing pigments) that act as cut-off filters of the incoming light. This narrows the absorption peak, shifting it to longer wavelengths before the light reaches the light sensitive part of the cones, and thereby reducing overlap between adjacent spectral types (Bowmaker 1991, Bowmaker et al. 1997; Maier 1994b). Consequently, birds differ from humans, not only in their sensitivity to the UV spectrum which increases the range of wavelengths over which they can see, but also in their superior ability to detect and discriminate spectral differences, perhaps even within the human visible spectrum.

There is nothing much explaining the connection between sensitivity and absorbance. Let me know if there is any detail that might help. Shyamal (talk) 01:20, 3 July 2009 (UTC)

The original ref of Hart 2000 is available here and the author's other publications are on http://www.uq.edu.au/~uqnhart/publications.htm Shyamal (talk) 02:28, 3 July 2009 (UTC)

Thanks; but now I'm very confused. I can't find the quoted figure caption or other text in the paper you pointed me at, or in any of Hart's other papers there. One of us is looking in the wrong place? Ah, here, I found it in this book; but I can't read it all. Oh, nevermind, I see that you were saying that book cites that 2000 paper; got it now.

Anyway, responsivity or sensitivity is a physiological response measure, which is often hard to get, whereas absorbance is a physical measurement, often easier. They correlate, pretty much, because a photon has to be absorbed to be detected. But lots of short-wavelength photons get absorbed where they don't do any good, rather than in the opsin, which is why the curves have those funny tails. Dicklyon (talk) 04:52, 3 July 2009 (UTC)

OK, here's the deal; he killed the birds and did microspectrophotometry on their retinas. Figs 1A, 2A, 3A, and 4A in the 2000 finches paper are like your drawing. But then he did difference between that absorbance data and a repeat after "bleaching" the pigments with white light, which makes the non-pigment-related "tails" go away; but the data gets noisier. In the "D" figures he shows the same curves, but also the adjusted data points. We could make a sketch of a curve fitted to those, too, and that would represent sensitivity better; or at least represent the opsin absorbance better. Dicklyon (talk) 05:21, 3 July 2009 (UTC)

I updated the figure description and source info a bit, and tightened up the bounding box so it makes a better thumbnail, and updated the caption and refs at tetrachromacy. Please verify. Dicklyon (talk) 05:40, 3 July 2009 (UTC)

Thanks for that, actually I only just realized that your context was the image use in tetrachomacy. I knew of its use only on the Bird vision page ! Shyamal (talk) 06:03, 3 July 2009 (UTC)