More Complex than Previously Thought-Part VII – The Retina

If you have ever taken a class in sensation and perception, you would have some notions about the astonishing complexity of the eye and perceptual processes.  Scientists had previously looked at an aspect of the retina as indicating flaws that potentially posed problems for high resolution vision.(1,2)

However, things were more complex than was previously thought:

In the April 7 issue of the journal PLOS Biology, the scientists say their findings suggest that the nervous system operates with higher precision than previously appreciated and that apparent irregularities in individual cells may actually be coordinated and finely tuned to make the most of the world around us.

Previously, the observed irregularities of individual receptive fields suggested that the collective visual coverage might be uneven and irregular, potentially posing a problem for high-resolution vision. “The striking coordination we found when we examined a whole population indicated that neuronal circuits in the retina may sample the visual scene with high precision, perhaps in a manner that approaches the optimum for high-resolution vision,” says senior author E.J. Chichilnisky, Ph.D., an associate professor in the Systems Neurobiology Laboratories.

All visual information reaching the brain is transmitted by retinal ganglion cells. Each of the 20 or so distinct ganglion cell types is thought to transmit a complete visual image to the brain, because the receptive fields of each type form a regular lattice covering visual space. However, within each regular lattice, the individual cells’ receptive fields have irregular and inconsistent shapes, which could potentially result in patchy coverage of the visual field.

To understand how the visual system overcomes this problem, postdoctoral researcher and first author Jeffrey L. Gauthier, Ph.D., used a microscopic electrode array to record the activity of ganglion cells in isolated patches of retina, the tissue lining the back of the eye.

After monitoring hundreds of ganglion cells over several hours, he distinguished between different cell types based on their light response properties. “Often people record from many cells simultaneously but they don’t know which cell belongs to which type,” says Gauthier. Without this information, he says, he wouldn’t have been able to observe that the receptive fields of neighboring cells of a specific type interlock, complementing each others’ irregular shapes.

“The receptive fields of all four cell types we examined were precisely coordinated,” he says, “but we saw no coordination between cells of different types, emphasizing the importance of clearly distinguishing one cell type from another when studying sensory encoding by a population of neurons.”

Darwinists like to claim that the eye is poorly designed (unless your an octopus).(3) However, if you study the eye in any serious detail, it would be extremely difficult to come to that conclusion. The assumption of poor design actually delays scientific advancement. Imagine if these researchers had adhered to Darwinian dogma, and viewed the ‘apparent irregularities’ of the eye as simply more evidence of bad design. If they had, it would have been a science-stopper. The scientists would most likely have not examined the matter any further.

I don’t know if these scientists are Darwinists or not. There were no appeals to the imagination, and there was a properly specified null hypothesis.(4)

The observed coordination of RFs produced more uniform visual sampling than expected by chance, as demonstrated using a geometric test. The null hypothesis was that visual sampling is no more uniform than expected from random interaction between irregular RF shapes, where “irregular” is defined as deviation from circular symmetry. Under this null hypothesis, mirroring each RF around its center point should not affect sampling uniformity [6]. To test this hypothesis, the arrangement of simultaneously recorded RFs of a single type (Figure 3A, first column) was compared to the arrangement obtained after each RF was artificially mirrored (Figure 3A, second column). Visual inspection showed that mirroring severely disrupted visual coverage: the area covered by exactly one RF contour (gray) was significantly reduced, and there were many more gaps (black) and overlaps (white). Thus RF shapes were not arranged randomly, but rather were coordinated in a way that provides more uniform coverage of visual space.

The authors of the study conclude with:

The present results have surprising implications for how populations of neurons produce an efficient and complete representation. Recorded in isolation, single neurons frequently exhibit irregular response properties, suggesting that large populations must rely on averaging or interpolation to produce accurate sensory performance or behavior (e.g., see [37–39]). The present results, however, show that in a complete population, irregular features can be integral to a finely coordinated population code. This suggests that the nervous system operates with a higher degree of precision than previously thought, and that irregularities in individual cells may actually reflect an unappreciated aspect of neural population codes (e.g., [40]).

The continuing Darwinist mantra of things “appearing” designed has passed the breaking point. In my opinion, this is no longer a tenable position to hold. If for no other reason, this idea should be abandoned because of its proven track record of inhibiting scientific discovery.

(1) How The Retina Works: Like A Multi-layered Jigsaw Puzzle Of Receptive Fields, Science Daily, April 7, 2009

(2) Gauthier JL, Field GD, Sher A, Greschner M, Shlens J, et al. (2009) Receptive Fields in Primate Retina Are Coordinated to Sample Visual Space More Uniformly. PLoS Biol 7(4): e1000063 doi:10.1371/journal.pbio.1000063

(3) Evolution: A Theory of Change? The Case of the Octopus. ID & More, March 18, 2009

(4) Science, ID, and Darwinism. ID & More, April 6, 2008


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