Seeing Vision in a New Light
The eye is like a camera, right? That picture is way too simplistic. The eye-brain visual system does image processing and gleans information from photons in diverse and remarkable ways. Here are some recent findings by scientists:
- Upward mobility: A team of Harvard scientists found some retinal ganglion cells that sense upward motion. Writing in Nature,1 they began,
The retina contains complex circuits of neurons that extract salient information from visual inputs. Signals from photoreceptors are processed by retinal interneurons, integrated by retinal ganglion cells (RGCs) and sent to the brain by RGC axons. Distinct types of RGC respond to different visual features, such as increases or decreases in light intensity (ON and OFF cells, respectively), colour or moving objects. Thus, RGCs comprise a set of parallel pathways from the eye to the brain….
….Here we show, by means of a transgenic marking method, that junctional adhesion molecule B (JAM-B) marks a previously unrecognized class of OFF RGCs…. These cells have asymmetric dendritic arbors aligned in a dorsal-to-ventral direction across the retina. Their receptive fields are also asymmetric and respond selectively to stimuli moving in a soma-to-dendrite direction; because the lens reverses the image of the world on the retina, these cells detect upward motion in the visual field. Thus, JAM-B identifies a unique population of RGCs in which structure corresponds remarkably to function.
- Got your number: The retina can also respond to a quality called “numerosity” – a nonverbal, visual sense of number. David Burr and John Ross, writing in Current Biology,2 summarized this unusual ability of the eye:
Evidence exists for a nonverbal capacity for the apprehension of number, in humans (including infants) and in other primates. Here, we show that perceived numerosity is susceptible to adaptation, like primary visual properties of a scene, such as color, contrast, size, and speed. Apparent numerosity was decreased by adaptation to large numbers of dots and increased by adaptation to small numbers, the effect depending entirely on the numerosity of the adaptor, not on contrast, size, orientation, or pixel density, and occurring with very low adaptor contrasts. We suggest that the visual system has the capacity to estimate numerosity and that it is an independent primary visual property, not reducible to others like spatial frequency or density of texture.
- Go with the flow: Many photographs and videos are taken with the camera fixed on a tripod. What happens to the visual scene in a movie when the camera is mounted on a galloping horse, train engine or race car? It certainly becomes more dynamic and much more difficult to process the information.
We saw that dragonflies are masters of optic flow, and that scientists are keen to imitate their special visual organ that processes the information from rapid forward direction (08/13/2004). Frank Bremmer summarized some new findings in Current Biology that says human eyes also have some of this ability.3 This gives us processing powers beyond the simple interpretation of an image coming through a lens.
Optic flow is a key signal for heading perception. A new study has shown that the human brain can dissociate between consistent (natural) and inconsistent flow, revealing what is likely a new hierarchy in visual motion processing.
He reported on recent “surprising findings” that showed certain areas of the visual cortex, labeled MST, VIP and CSv, appear to be processing stations for optic flow information.
Taken together, these new results suggest that area MST may be a preprocessing stage acting like a tuned filter for visual self-motion signals. Areas VIP and CSv, on the other hand, could be seen as downstream processing stages judging the ecological validity of the self-motion signals. This interpretation would indicate a previously unknown hierarchy within the human visual cortical motion system.
- Color me blue: Brian Wandell, Stanford psychologist, wrote in Current Biology about another stimulating fact: the colors activated by the cones that react to red, green or blue when those colors come through the lens (or are transmitted from video pixels) also “see” the corresponding colors when the neurons themselves are stimulated.4 Commenting on a study of a patient that had electrodes implanted into the visual cortex, he said:
Directly stimulating certain cortical neurons can produce a color sensation; a case is reported in which the color perceived by stimulation is the same as the color that most effectively excites the cortical circuitry….
These results teach us that even the simplest stimulation is capable of stirring up a perceptually meaningful response from the cortical circuitry. One possibility is that the complex molecular and neural circuitry that serves this portion of the brain is tolerant of a wide range of potential inputs, and that nearly any stimulation of this circuitry evokes a characteristic (resonant) response. The resonant response of these specific circuits is the experience of color.
To avoid human chauvinism, let’s look into the eyes of some animals living underwater that can, in certain ways, outperform our own visual tricks. The winner in both cases is among the humblest creatures you would ever suspect to find such abilities: the mantis shrimp.
- Polar opposites: For the first time, scientists found an animal with the ability to discern circularly polarized light: the mantis shrimp. An international team of scientists reported this in Current Biology5 with some obvious pride at being #1 to discover this feat:
We describe the addition of a fourth visual modality in the animal kingdom, the perception of circular polarized light. Animals are sensitive to various characteristics of light, such as intensity, color, and linear polarization. This latter capability can be used for object identification, contrast enhancement, navigation, and communication through polarizing reflections. Circularly polarized reflections from a few animal species have also been known for some time. Although optically interesting, their signal function or use (if any) was obscure because no visual system was known to detect circularly polarized light. Here, in stomatopod crustaceans, we describe for the first time a visual system capable of detecting and analyzing circularly polarized light. Four lines of evidence—behavior, electrophysiology, optical anatomy, and details of signal design—are presented to describe this new visual function. We suggest that this remarkable ability mediates sexual signaling and mate choice, although other potential functions of circular polarization vision, such as enhanced contrast in turbid environments, are also possible. The ability to differentiate the handedness of circularly polarized light, a visual feat never expected in the animal kingdom, is demonstrated behaviorally here for the first time.
- Super sight: In the latest issue of Creation magazine (March-May, 2008),6 Jonathan Sarfati described one amazing feature of the mantis shrimp, its Guinness-level power punch: it can flick its snapper at 51 mph, generating an acceleration of 10,600 g. But that’s not all. In a sidebar, he talked about another Guinness-level ability: the shrimp’s “super sight.” Would you believe this little crustacean has one of the world’s most complex color vision systems?
While humans have three different types of colour receptor (red, green and blue), the shrimp has 12. Four of these can see in the ultraviolet, which we can’t. Furthermore, they can tune their vision with special transparent colour filters to compensate for the way water absorbs different colours differently.
None of the above articles mentioned evolution once.
1. Kim, Zhang, Yagamata, Meister and Sanes, “Molecular identification of a retinal cell type that responds to upward motion,” Nature 452, 478-482 (27 March 2008) | doi:10.1038/nature06739.
2. David Burr and John Ross, “A Visual Sense of Number,” Current Biology, Vol 18, 425-428, 25 March 2008, http://dx.doi.org/10.1016/j.cub.2008.02.052.
3. Frank Benner, “Visual Neuroscience: The Brain’s Interest in Natural Flow,” Current Biology, Volume 18, Issue 6, 25 March 2008, Pages R263-R265, http://dx.doi.org/10.1016/j.cub.2008.01.023.
4. Brian Wandell, “Colour Vision: Cortical Circuitry for Appearance,” Current Biology, Volume 18, Issue 6, 25 March 2008, Pages R250-R251, doi:10.1016/j.cub.2008.01.045.
5. Chou, Kleinlogel, Cronin, Caldwell, Loeffler, Siddiqi, Goldizen and Marshall, “Circular Polarization Vision in a Stomatopod Crustacean,” Current Biology, Volume 18, Issue 6, 25 March 2008, Pages 429-434, doi:10.1016/j.cub.2008.02.066.
6. Jonathan Sarfati, “Shrimpy superboxer,” Creation magazine, Volume 30, Issue 2, Published March 2008, pp. 12-13.
Isn’t this terrific? What amazing things are found in nature. The eye gave Darwin cold shudders, but now we know that it is far more complex than he knew. And some of the most remarkable capabilities reside in the humblest of creatures. Shrimp are crustaceans – a subphylum of arthropods, whose members extend all the way back to the Cambrian. This means that the lowest fossil layers containing multicellular animals already display these technologies (10/04/2007).
This circuitry and the complex processing software did not emerge by chance. Each of these capabilities are systems involving hardware and software. They require programmed analysis and response to sensory inputs. Eyes are able to extract all kinds of interesting information from light, much more than you would think from the simple diagram in most textbooks of an inverted camera-like image on a retina.
The research done to find these abilities was done in intelligently-designed labs by intelligent scientists using reverse-engineering principles. Intelligent design is present de facto from beginning to end. Evolution is blind, they say; well, evolutionary theory is also blind. Take off the blinders and see the creation through created eyes.