Could one's
chronotype (degree of "morningness" vs. "eveningness") be related to your membership on Team white/gold vs. Team blue/black?
Dreaded by night owls everywhere, Daylight Savings Time forces us to get up an hour earlier. Yes,
[my time to blog and] I have been living under a rock, but this evil event and an old tweet by
Vaughan Bell piqued my interest in
melanopsin and
intrinsically photosensitive retinal ganglion cells.
I thought this was a brilliant idea, perhaps differences in
melanopsin genes could contribute to differences in brightness perception. More about that in a moment.
{Everyone already knows about #thedress from Tumblr and Buzzfeed and Twitter obviously}
In the initial BuzzFeed poll,
75% saw it as white and gold, rather than the actual colors of
blue and black. Facebook's more systematic research estimated this number was only
58% (and influenced by probably exposure to
articles that used Photoshop). Facebook also reported differences by sex (males more b/b), age (youngsters more b/b), and interface (more b/b on computer vs. iPhone and Android).
Dr. Cedar Riener wrote two
informative posts about why people might perceive the colors differently, but Dr. Bell was
not satisfied with this and other explanations.
Wired consulted two experts in color vision:
“Our visual system is supposed to throw away information about the illuminant and extract information about the actual reflectance,” says Jay Neitz, a neuroscientist at the University of Washington. “But I’ve studied individual differences in color vision for 30 years, and this is one of the biggest individual differences I’ve ever seen.”
and
“What’s happening here is your visual system is looking at this thing, and you’re trying to discount the chromatic bias of the daylight axis,” says Bevil Conway, a neuroscientist who studies color and vision at Wellesley College. “So people either discount the blue side, in which case they end up seeing white and gold, or discount the gold side, in which case they end up with blue and black.”
Finally, Dr. Conway threw out the chronotype card:
So when context varies, so will people’s visual perception. “Most people will see the blue on the white background as blue,” Conway says. “But on the black background some might see it as white.” He even speculated, perhaps jokingly, that the white-gold prejudice favors the idea of seeing the dress under strong daylight. “I bet night owls are more likely to see it as blue-black,” Conway says.
Melanopsin and Intrinsically Photosensitive Retinal Ganglion Cells
Rods and cones are the primary
photoreceptors in the retina that convert light into electrical signals. The role of the third type of photoreceptor is very different.
Intrinsically photosensitive retinal ganglion cells (ipRGCs) sense light without vision and:
- ...contribute to the regulation of pupil size and other behavioral responses to ambient lighting conditions...
- ...contribute to photic regulation of, and acute photic suppression of, release of the hormone melatonin...
Recent research suggests that ipRGCs may play more of a role in visual perception than was originally believed. As Vaughan said,
melanopsin (the photopigment in ipRGCs) is involved in
brightness discrimination and is most sensitive to blue light.
Brown et al. (2012) found that melanopsin knockout mice showed a change in spectral sensitivity that affected brightness discrimination; the KO mice needed higher green radiance to perform the task as well as the control mice.
The figure below shows the spectra of human cone cells most sensitive to Short (S), Medium (M), and Long (L) wavelengths.
Spectral sensitivities of human cone cells, S, M, and L types. X-axis is in nm.
The peak spectral sensitivity for melanopsin photoreceptors is in the blue range. How do you isolate the role of melanopsin in humans?
Brown et al. (2012) used
metamers, which are...
...light stimuli that appear indistinguishable to cones (and therefore have the same color and photopic luminance) despite having different spectral power distributions. ... to maximize the melanopic excitation achievable with the metamer approach, we aimed to circumvent rod-based responses by working at background light levels sufficiently bright to saturate rods.
They verified their approach in mice, then used a four LED system to generate stimuli that diffed in presumed melanopsin excitation, but not S, M, or L cone excitation. All six of the human participants perceived greater brightness as melanopsin excitation increased (see Fig. 3E below). Also notice the individual differences in test radiance with the fixed 11% melanopic excitation (on the right of the graph).
Modified from Fig. 3E (Brown et al. (2012). Across six subjects, there was a strong correlation between the test radiance at equal brightness and the melanopic excitation of the reference stimulus (p < 0.001).1
Maybe Team white/gold and Team blue/black differ on this dimension? And while we're at it, is variation in melanopsin related to circadian rhythms, chronotype, even
seasonal affective disorder (SAD)?
2 There is some evidence in favor of the circadian connections. Variants of the melanopsin (Opn4) gene might be related to
chronotype and to
SAD, which is much more common in women. Another Opn4 polymorphism may be related to
pupillary light responses, which would affect light and dark adaptation. These genetic findings should be interpreted with caution, however, until replicated in larger populations.
Could This Device Hold the Key to “The Dress”?
ADDENDUM (March 10 2015): NO, according to Dr. Geoffry K. Aguirre of U. Penn.: “Speaking as a guy with a 56-primary version of This Device to study melanopsin, I think the answer to your question is 'no'…” His PNAS paper, Opponent melanopsin and S-cone signals in the human pupillary light response, is freely available.3
A recent method developed by
Cao, Nicandro and Barrionuevo (2015) increases the precision of isolating ipRGC function in humans. The four-primary photostimulator used by
Brown et al. (2012) assumed that the rod cells were saturated at the light levels they used. However,
Cao et al. (2015) warn that “a four-primary method is not sufficient when rods are functioning together with melanopsin and cones.” So they:
...introduced a new LED-based five-primary photostimulating method that can independently control the excitation of melanopsin-containing ipRGC, rod and cone photoreceptors at constant background photoreceptor excitation levels.
Fig. 2 (Cao et al., 2015). The optical layout and picture of the five-primary photostimulator.
Their
Journal of Vision article is freely available, so you can read all about the methods and experimental results there (i.e., I'm not even going to try to summarize them here).
So the question remains: beyond the many perceptual influences that everyone has already discussed at length (e.g., color constancy, Bayesian priors, context, chromatic bias, etc.), could variation in ipRGC responses influence how you see “The Dress”?
Footnotes
1Fig 3E (continued). The effect was unrelated to any impact of melanopsin on pupil size. Subjects were asked to judge the relative brightness of three metameric stimuli (melanopic contrast −11%, 0%, and +11%) with respect to test stimuli whose spectral composition was invariant (and equivalent to the melanopsin 0% stimulus) but whose radiance changed between trials.
2 This would test Conway's quip that night owls are more likely to see the dress as blue and black.
3 Aguirre also said that a contribution from melanopsin (to the dress effect) was doubtful,
at least from any phasic effect: “It's a slow signal with poor spatial
resolution and subtle perceptual effects.” It remains to be seen whether
any bias towards discarding blue vs. yellow illuminant information is affected by chronotype.
Interesting result from Spitschan, Jain, Brainard, & Aguirre 2014):
The opposition of the S cones is revealed in a seemingly paradoxical dilation of the pupil to greater S-cone photon capture. This surprising result is explained by the neurophysiological properties of ipRGCs found in animal studies.
References
Brown, T., Tsujimura, S., Allen, A., Wynne, J., Bedford, R., Vickery, G., Vugler, A., & Lucas, R. (2012). Melanopsin-Based Brightness Discrimination in Mice and Humans. Current Biology, 22 (12), 1134-1141 DOI: 10.1016/j.cub.2012.04.039
Cao, D., Nicandro, N., & Barrionuevo, P. (2015). A five-primary photostimulator suitable for studying intrinsically photosensitive retinal ganglion cell functions in humans. Journal of Vision, 15 (1), 27-27 DOI: 10.1167/15.1.27
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