Thursday, July 28, 2011

Another study adding to the confusion about human variation in visual acuity: do white folks and autistics have better eyes or bigger eyeballs?

Holey Moley! I'm so confused I can't see straight! I'm still scratching my head over the scientific weirdness of claims and counterclaims that autistic people have the visual acuity of birds of prey, and I'm still trying to find time in my busy family life to read all the papers and published correspondence on that strange matter, and after taking the kids to see a display of living birds of prey from an animal shelter that was at a local shopping centre I'm pretty sure there are some major physical differences between an eagle's visual system and a human one, and now, while idly browsing the internet at the science department of the ABC's popular website, what do I see? I see, with my apparently atypical but most certainly not flawless visual system, a story about claims by an Oxford University researcher that he and a co-author have found that people from higher latitudes have greater visual acuity and have bigger eyeballs that go along usefully with bigger brains to process that visual input. The researcher went on to theorize that it is the parts of the brain that process vision that are beefed-up, rather than the frontal parts of the brain, to compensate for the lower levels of light at light-deprived places like polar regions, which makes it harder to see stuff. (I've got to wonder, if low-light conditions are such a bad thing for seeing, why is it that so many Australians routinely wear dark sunglasses, many wearing them all through the year, even on overcast, wintry days? Why do people wear sunglasses? Fashion? To conceal identity? Light sensitivity from an hangover or headache? To hide red eyes from cannabis use or from crying? To conceal an ugly face? Irrational fear of eye damage from UV rays? This has always been a mystery to me. I can't think of anything that I'd less want to do than put a barrier between my eyes and a world that I want to see.)

The most striking claims about visual acuity of people from polar regions, which have apparently been published in some publication of the Royal Society, triggered in my weirdly-wired mind many lines of thought and many questions. Firstly, the claim that people from polar regions have greater visual acuity seems extraordinary in light of something that I've just read in some of the published correspondence about the 2009 paper about visual acuity and autism by Emma Ashwin, Prof. Simon Baron-Cohen and team. In that published letter questioning the findings of the original 2009 research paper Bach and Dakin wrote "Specifically, Ashwin et al. report mean decimal visual acuities of 2.79 in their group of observers with ASD and 1.44 in an age-matched control group..... If true, Aswin et al.'s finding would be very important for two reasons. First, as far as we are aware, this is the first report of consistently superior VA in any clinical population (neuropsychological or otherwise)." "VA" stands for "visual acuity". This letter was published in 2009, so I guess it is possible that research has been published since then finding superior visual acuity in some human group or groups since then, but nevertheless, the claim that there are evolved regional racial variations in human visual acuity, eyeball size and brain size seems pretty extraordinary, and surely controversial.

Is it really true that some racial groups, specifically human populations that evolved in regions of high latitudes, who would certainly have what we call "white skin", and who apparently are now known to have some genes that originated from Neanderthals, have greater visual acuity and larger brains? This seems to be a claim designed to provoke outrage from left-leaning people who oppose racism and fans of the late archaeologist and pop science writer Stephen Jay Gould, the Harvard University professor who wrote the award-winning and often quoted pop science book The Mismeasure of Man, which was published in 1981. In this book Gould apparently debunked some old research that found racial differences in skull sizes. I read this book myself, and was most impressed by the style of the book, but I didn't "buy" the ideas put forward by Gould. As a book it was entertainingly and engagingly written, and for this Gould deserves the credit for making science interesting to a mass readership. As for the facts in the book - I knew that I personally had no means to independently check Gould's basic research reinterpreting Morton's work on skulls, so I had to base my opinions of Gould's research on whether or not I thought his own interpretation was unbiased. How could I judge that? I was unconvinced by Gould's arguments against the concept of quantifying intelligence through IQ testing. I couldn't see why controversy should be a reason for choosing to not measure anything. Psychologists appeared to have no problem with the idea of a measurable general level of intelligence ("g"). Gould was not a psychologist, he was a paleontologist and a biologist. What business did Gould have disputing a basic concept in psychology?

If I remember it correctly, in this book Gould argued that some past scientific research about skull size and race was biased in favour of the white races appearing to have larger brains, and this bias was supposedly due to the unconscious racist biases of Samuel Morton, the researcher, influencing his taking of measurements. Well, I'm amazed that I've been confronted with so many interesting inter-related ideas in science recently, and just a week or so ago I noticed that in New Scientist magazine was published a most interesting article about a PLoS Biology paper in which researchers have overturned Gould's argument by rechecking many of the skulls that Morton studied, and they have concluded that it was Gould who was biased, not Samuel George Morton, the original measurer of skulls. I'm so disappointed that no one can sue over this matter; Gould is dead, and Morton is long-dead. I'm sure that Pearce and Dunbar's research will add to that great eternal bunfight over race and brains and intelligence. I love it! (Did you ever read the book The 10,000 Year Explosion by Cochran and Harpending? Most thought-provoking bunfight-fodder.)

What do I think about the new claims about visual acuity and race? I'm most sceptical, in light of the debacle over the 2009 paper about visual acuity and autism. Researchers from universities such as Oxford or Cambridge no longer have instant credibility in my mind. I'm far from convinced that the researchers are able to make claims about regions of evolution and visual acuity and brain size based on studying skulls, which is apparently one of the things that are the basis of their research. What would Stephen Jay Gould have to say about this research? If he was still alive today, I'm sure his commentary on this research would make very entertaining reading. As a know-it-all housewife, I've got to wonder, couldn't variations in the sizes of orbital volumes simply be a reflection of the proportion of Neanderthal heritage that a racial group has? The Neanderthals appeared to have very large eye sockets compared to Homo sapien skulls. According to respectable scientific sources, white people do have Neanderthal genes more than other racial groups, and the Neanderthals were adapted to cold regions. I guess Pearce and Dunbar could interpret this as supporting their theory.

The idea that large eyes are necessarily eyes with better vision doesn't impress me as realistic. Pearce and Dunbar don't seem to be aware of important barriers between nocturnal and diurnal lifestyles in relation to the eyes. People who live in polar regions are not nocturnal animals, and there are important differences between them and the nocturnal animals which have evolved to have large eyes. Anyone who has gone camping in an Australian national park that has possums in it will be aware that large eyes that have evolved for nocturnal use can be eyes that are vulnerable to serious problems if the animal does not maintain a natural nocturnal lifestyle. National park visitors are often told to not feed possums during the day, as possums who are unnaturally active during the daylight hours because of human interaction apparently eventually go blind. The blind obviously don't have good visual acuity.

Glancing down Pearce and Dunbar's piece, I notice that in Figure 2 there are data points in which some human populations apparently have mean visual acuity between 2.5 and 2.75. That level of visual acuity appears to be pretty close to the level claimed for the autistic group in Aswin, Baron-Cohen and colleagues controversial 2009 paper, if I'm reading things correctly. So who are these extraordinary human populations who have visual acuity of damn-close to that of a bird of prey? I think it would be wise to leave it to vision scientists to recheck the data used by Pearce and Dunbar, but I can say that their data is based on very, very old anthropological research. Remember what Bach and Dakin wrote about the 2009 paper claiming extraordinary visual acuity in autistics? " far as we are aware, this is the first report of consistently superior VA in any clinical population (neuropsychological or otherwise)." Hmmmm. I wonder what Bach and Dakin would have to say about Pearce and Dunbar's research?

I have doubts that Pearce and Dunbar's ideas will stand up to scrutiny, but if they do, I will be wondering about any possible connections between those ideas about race, visual acuity and selective enhancement of visual processing areas of the brain and a theory of autism that I find interesting, the Enhanced Perceptual Functioning Model of Autism from Laurent Mottron's team. My reading of this model is that it is consistent with autistic people having many enhanced perceptual abilities, including visual, but I don't think including visual acuity, and the basis for this being a selective enhancement of the parts of the brain at the rear that are responsible for processing sensory input, but with a relatively less developed frontal area of the brain. Is it possible that this type of brain is an evolutionary adaptation to some particular environment? Some particular geographical region? Low light levels? A semi-nocturnal lifestyle? A solitary, foraging lifestyle? Is the Enhanced Perceptual Functioning Model of Autism compatible with Jared Reser's interesting Solitary Forager Hypothesis of Autism? I think it could be. I believe these exciting theories are where the real future of the scientific study of autism and human variation in visual ability lies.

I'm not sure what to make of all this, but I think the wisdom of the truism that academics shouldn't delve into areas of research in which they don't have expertise continues to be ignored and later demonstrated. Will they never learn? I also believe I might have uncovered an interesting new law of science. It appears that there could be an inverse relationship between the reliability of a scientific theory endorsed by a writer, and the level of social prestige of the organization that the writer works for. This is a type of academic freedom that I don't think I'd support. You can't believe everything that a writer from the University of Cambridge, or a writer from the University of Oxford, or a writer from Harvard University, or a writer from the Australian Broadcasting Commission writes, just because they are from Cambridge, Oxford, Harvard or the ABC. Crap can fall from high places. Reader beware!

References about research on visual acuity by Pearce and Dunbar

Viegas, Jennifer (2011) Polar people have bigger eyes and brains. ABC Science. 27 July 2011

Pearce, Eiluned and Dunbar, Robin (2011) Latitudinal variation in light levels drives human visual system size. Biology Letters. Published online before print July 27, 2011, doi: 10.1098/rsbl.2011.0570

References about Gould and skull sizes and race

DeGusta, David and Lewis, Jason E. (2011) Gould's skulls: Is bias inevitable in science? New Scientist. Issue 2822 25 July 2011
[Overall, we found no evidence that Morton's bias had affected his results. Gould, in contrast, made a number of clear errors, all connected with his own presumed bias towards there being a lack of differences between populations.]

Lewis JE, DeGusta D, Meyer MR, Monge JM, Mann AE, et al. (2011) The Mismeasure of Science: Stephen Jay Gould versus Samuel George Morton on Skulls and Bias. PLoS Biology. 9(6): e1001071. doi:10.1371/journal.pbio.1001071 Published: June 7, 2011

Wikipedia contributors (accessed 2011) The Mismeasure of Man. Wikipedia, The Free Encyclopedia.

References about the Enhanced Perceptual Functioning Model of Autism

Mottron, Laurent, Dawson, Michelle, Soulieres, Isabelle, Hubert, Benedicte and Burack, Jake (2011) Enhanced Perceptual Functioning in Autism: An Update, and Eight Principles of Autistic Perception. Journal of Autism and Developmental Disorders. Vol. 36, No. 1, January 2006 DOI 10.1007/s10803-005-0040-7 Published Online: February 2, 2006
[The overfunctioning of brain regions typically involved in primary perceptual functions may explain the autistic perceptual endophenotype.]

Samson, Fabienne, Mottron, Laurent, Soulieres, Isabelle and Zeffiro, Thomas A. (2011) Enhanced visual functioning in autism: an ALE meta-analysis. Human Brain Mapping. first published online: 4 APR 2011 DOI: 10.1002/hbm.21307
[The stronger engagement of the visual system, whatever the task, represents the first physiological confirmation that enhanced perceptual processing is a core feature of neural organization in this population.]

Reference about the Solitary Forager Hypothesis of Autism

Reser, Jared Edward (2011) Conceptualizing the Autism Spectrum in Terms of Natural Selection and Behavioral Ecology: The Solitary Forager Hypothesis. Evolutionary Psychology. – 2011. 9(2): 207-238

References about or relevant to research by Ashwin, Baron-Cohen and others about visual acuity and autism (in chronological order)

Ashwin E, Ashwin C, Rhydderch D, Howells J, Baron-Cohen S. (2009) Eagle-eyed visual acuity: an experimental investigation of enhanced perception in autism. Biological Psychiatry. 2009 Jan 1;65(1):17-21. Epub 2008 Jul 23.
["Individuals with ASC have significantly better visual acuity (20:7) compared with control subjects (20:13)—acuity so superior that it lies in the region reported for birds of prey."]

Bach, M. Dakin, SC (2009) Regarding "Eagle-eyed visual acuity: an experimental investigation of enhanced perception in autism". Biological Psychiatry. 2009 Nov 15;66(10):e19-20. Epub 2009 Jul 3.
[Correspondence. "Prompted by the highly counterintuitive nature of both these conclusions and the finding that inspired them, we have investigated the procedure employed by the authors of this study....We report that although there are real behavioural differences between ASD and control groups, technical limitations in the procedure used to measure acuity call into question the conclusion that people with ASD have higher visual acuity compared with unaffected individuals without the context of the experiment."]

Crewther DP, Sutherland A (2009) The more he looked inside, the more piglet wasn't there: is autism really blessed with visual hyperacuity? Biological Psychiatry. 2009 Nov 15;66(10):e21-2. Epub 2009 Jun 27.
[Correspondence. "Thus, the estimates gained for both ASD and normal individuals were all extrapolations beyond the range of acuity value testable with that viewing distance." "The main conclusion of Ashwin et al., that the foveal cone denisty is higher...also does not bear up in comparison with the hawk eye....Thus, it seems that in nature, greater resulotion is achieved by greater eyeball size,... than by closer packing. It is clear that the eyes of autistic individuals are not twice as large as normal." "It is possible that the large number of trials might have contributed to concentration lapses in the control subjects, widening the gap in this extrapolated estimation of acuity between normal subjects and autistic subjects."]

Ashwin E, Ashwin C, Tavassoli T, Chakrabarti B, Baron-Cohen S. (2009) Eagle-eyed visual acuity in autism. Biological Psychiatry. 2009 Nov 15;66(10) e23-4. Epub 2009 Jul 3.
[Correspondence. "We accept that the technical issues outlined in the commentary need to be resolved."]

Kéïta, Luc, Mottron, Laurent and Bertone, Armando (2010) Far visual acuity is unremarkable in autism: Do we need to focus on crowding? Autism Research. Vol 3 Issue 6 p.333-341 December 2010. Article first published online: 6 OCT 2010DOI: 10.1002/aur.164
["...the expected crowding effect at one gap-size opening distance was evidenced for the control group only.....These results suggest that although far visual acuity is unremarkable in autism, altered local lateral connectivity within early perceptual areas underlying spatial information processing in autism is atypical."]

Bölte S, Schlitt S, Gapp V, Hainz D, Schirman S, Poustka F, Weber B, Freitag C, Ciaramidaro A, Walter H. (2011) A Close Eye on the Eagle-Eyed Visual Acuity Hypothesis of Autism. Journal of Autism and Developmental Disorders. 2011 Jun 10. [Epub ahead of print]
["This study could not confirm the eagle-eyed acuity hypothesis of ASD, or find evidence for a connection of VA and clinical phenotypes."]

Tavassoli T, Latham K, Bach M, Dakin SC, Baron-Cohen S. (2011) Psychophysical measures of visual acuity in autism spectrum conditions. Vision Research. 2011 Jun 16. [Epub ahead of print]
["Best corrected VA was significantly better than the initial habitual acuity in both groups, but adults with and without ASC did not differ on ETDRS or FrACT binocular VA." ]

No comments: