The Machinery Behind the Senses
There’s a lot of physical work our eyes, ears, and brain cells perform to support our perceptions of the world.
Blind man’s bluff: There’s only a small area of sharp vision, about the size of a fingernail at arm’s length, Science Daily says. That’s the area the fovea (densest region of receptors in the retina) can image at a time. Why, then, do we “think” we have sharp vision in the whole field of view? “The brain leads us to believe we have sharp vision,” researchers at Bielefeld University in Germany found; our brain essentially “fools” us into that belief. What does their paper announce? “Its central finding is that our nervous system uses past visual experiences to predict how blurred objects would look in sharp detail.” The lead researcher concluded, “We do not see the actual world, but our predictions.”
Cookie cutter cochlea: The tiny hair cells in the cochlea (inner ear) must be laid out in the right pattern during development, or else deafness can result. Researchers from Howard Hughes Medical Institute and Rockefeller University, publishing in PNAS, devised a model based on what is known about the molecular mechanisms involved in hair cell morphogenesis. The model recreates the “hexagonal Turing pattern” that is established during development. A short video clip on the front page shows the the hair cells coming out like cookies on an assembly line, forming hexagonal arrays. Here’s the significance of their research:
Our senses of hearing and balance rest upon the activity of hair cells, the ear’s sensory receptors. Each hair cell detects mechanical stimuli with its hair bundle, an organelle comprising 10–300 cylindrical, actin-filled stereocilia. A bundle’s structure is highly stereotyped: the stereocilia stand erect in a regular, hexagonal array and display a monotonic gradient in length along one axis. This precise organization is key to the operation of the hair bundle: mutations that disturb the morphology of the bundle generally result in deafness. Here we provide a detailed mathematical model of hair-bundle morphogenesis that reproduces the essential features of bundles. The model also permits prediction of the effects of mutations, some of which have already been observed.
Insulated wiring: What happens in the brain when you learn a new motor skill? “To learn is to myelinate,” Science Magazine says. Learning a new skill switches on the production of oligodendrocytes, specialized brain cells that create myelin that sheaths certain neurons. “The finding advances our understanding of brain plasticity and points to roles for glia and myelin in cognitive function,” Long and Corfas say about the research paper in the same issue, “Motor skill learning requires active central myelination.” A summary on Medical Xpress shows an image of oligodendrocytes. It says that we need this constituent of white matter in addition to the more well-known gray matter:
New evidence of myelin’s essential role in learning and retaining new practical skills, such as playing a musical instrument, has been uncovered by UCL research. Myelin is a fatty substance that insulates the brain’s wiring and is a major constituent of ‘white matter’. It is produced by the brain and spinal cord into early adulthood as it is needed for many developmental processes, and although earlier studies of human white matter hinted at its involvement in skill learning, this is the first time it has been confirmed experimentally.
Default business: The brain never takes a complete break. What’s going on in your brain when your mind is at rest? A picture of the “default mode network” is shown in an article on Medical Xpress that tries to answer that question. Like the basal metabolic rate, the default mode network is taking care of business when there’s no concentrated effort. While most neuroscientists examine what happens when subjects think, Marcus Raichle (Washington University in St. Louis) has been a pioneer at looking at the quiet brain:
“A great deal of meaningful activity is occurring in the brain when a person is sitting back and doing nothing at all,” says Raichle, who has been funded by the National Science Foundation (NSF) Division of Behavioral and Cognitive Sciences in the Directorate for Social, Behavioral and Economic Sciences. “It turns out that when your mind is at rest, dispersed brain areas are chattering away to one another.”
Readers can learn about Raichle’s experiments to listen in on the chatter, such as “memory of personal events, evaluation of sensory information from the environment and body critical for decision making.” This is all being processed by your subconscious mind without your control. “The brain is capable of so many things, even when you are not conscious,” he says.
Yesterday’s post discussed near-death experiences. We saw that some patients in a vegetative state are still capable of willing their brains to imagine activities. We see today that the brain is in a constant state of default activity, even when the mind is “blank.” We know that, in sleep, we can experience dreams so vivid, we would swear our eyes and ears are perceiving realities that, on waking, we find to evaporate into fantasylands of our own imagination.
There is so much cellular activity, tissue activity and organ activity going on in between the “real world” and the mind, it’s bound to keep philosophers busy with the “mind-body problem” for many years, trying to reason how reliable our sensations might be. We just learned that our eyes “fool us” into thinking we see the world sharper than our retinas can bear. In a real sense, therefore, we’re not seeing reality; we’re seeing what our brain predicts it should look like! Tell that to the skeptic who only believes what he can see.
One thing we cannot exclude from experience, though, is our own consciousness. If you haven’t seen the video clip by David Chalmers on the “hard problem of consciousness” that we’ve recommended, this is a good time to watch it (about 9 minutes). To hope for understanding the world, we must have necessary and sufficient causes to explain the world. This must come from an intelligent, truthful, personal source able to communicate it to us on our level. You can’t get that from the bottom up (see article on Evolution News & Views). The only world view that can satisfy those prerequisites for reliable perception and reasoning is the world view that was communicated to us by the Creator, His word. “In the beginning was the Word… that lights every man that comes into the world” (John 1:1-18).