Neuroscientist David Eagleman, in his brilliant TED talk "Can We Create New Senses For Humans?", touches on this with a concept he calls the umwelt -- the slice of the objective reality we're aware of. That differs from animal to animal -- as he points out, for dogs, the umwelt is all about smell; it's sound-related for echolocating bats; it consists of electrical field fluctuations for the black ghost knife-fish; and so on. Eagleman says:
What this means is that our experience of reality is constrained by our biology. And that goes against the common-sense notion that our eyes and our ears and our fingertips are just picking up the objective reality that's out there. Instead, our brains are sampling just a little bit of the world... Now, presumably, every animal assumes that its umwelt is the entire objective reality out there, because why would you ever stop to imagine that there's something beyond what we can sense? Instead, what we all do is that we accept reality as it's presented to us.What never ceases to amaze me is that even the parts of the human umwelt most of us are pretty good at picking up on are still made largely of faulty and incomplete information. Our brains have evolved to fill in the gaps in what we see and hear -- so your perception of the world is built of what you're actually sensing of the real world, and what your brain assumes is there and fills in for you. (That it sometimes does this incorrectly is the basis of a lot of optical illusions.)
If you need further evidence that you're seeing some bits of reality but otherwise just kind of making shit up, consider a paper published this week in Proceedings of the National Academy of Sciences, by Michael Cohen (of Amherst College) and Thomas Botch and Caroline Robertson (of Dartmouth University). In "The Limits of Color Awareness During Active, Real-World Vision," Cohen, Botch, and Robertson tested something that's been known for years -- that the acuity of our color vision in the periphery of our visual field is fairly poor -- and challenged the prevailing explanation, which is that cones (our color-sensitive retinal cells) are dense in the fovea (center of the retina) and sparse in the edges.
[Image is in the Public Domain]
However, Cohen, Botch, and Robertson did an experiment that turns the whole question upside down. They gave test subjects head-mounted visual displays that were equipped with devices for tracking eye movements. They then showed the test subjects images of outdoor scenes, and without alerting them, began to decrease the color saturation in the edges of the image. The test subjects failed to notice the fact that the image was gradually turning to black-and-white from the edges inward until the colored bit spanned an angle of only 37.5 degrees, something that "does not correspond to known limitations imposed by retinal or neuroanatomy."
It appears that what's going on is that the edges of our visual field are reasonably good at recognizing color, but our brain simply ignores the input. Motion, on the other hand, is quickly detected even in the peripheral vision; makes some sense evolutionarily, where seeing the lion coming up from behind you is way more critical than determining what color his fur is.
It was a fairly shocking result even for the researchers. "We were amazed by how oblivious participants were when color was removed from up to 95 percent of their visual world," said study senior author Caroline Robertson, in an interview with EurekAlert. "Our results show that our intuitive sense of a rich, colorful visual world is largely incorrect. Our brain is likely filling in much of our perceptual experience."
How and why the brain does this, however, is still a mystery. The authors write:
If color perception in the real world is indeed as sparse as our findings suggest, the final question to consider is how this can be. Why does it intuitively feel like we see so much color when our data suggest we see so little? While we cannot offer a definitive answer, several possibilities can be explored in future research. One possibility is that as observers spend time in an environment, their brains are able to eventually “fill-in” the color of many items in the periphery. Of course, providing direct evidence for this explanation is challenging since it is extremely difficult to differentiate between scenarios where a subject knows the color of an object (i.e., “I know the tree behind me is green even though I currently cannot see the color green”) from instances where the subject is experiencing the color of that object online (i.e., “I can see the color green at this very moment”).So our umwelt is apparently an even smaller slice of reality than we'd thought. A little humbling, and something to think about next time you're in an argument with someone and you are tempted to say, "I know it happened that way, I saw it with my own eyes."
This week's Skeptophilia book-of-the-week is for people who are fascinated with the latest research on our universe, but are a little daunted by the technical aspects: Space at the Speed of Light: The History of 14 Billion Years for People Short on Time by Oxford University astrophysicist Becky Smethurst.
A whirlwind tour of the most recent discoveries from the depths of space -- and I do mean recent, because it was only released a couple of weeks ago -- Smethurst's book is a delightful voyage into the workings of some of the strangest objects we know of -- quasars, black holes, neutron stars, pulsars, blazars, gamma-ray bursters, and many others. Presented in a way that's scientifically accurate but still accessible to the layperson, it will give you an understanding of what we know about the events of the last 13.8 billion years, and the ultimate fate of the universe in the next few billions. If you have a fascination for what's up there in the night sky, this book is for you!
[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]
Post a Comment