Have you ever looked desperately for something—your passport perhaps—and then found, half an hour later, that it was right in front of you all the time? Inconspicuous but not really invisible? “Hiding in plain sight,” as the saying goes. It happens to everyone. We wonder why we didn’t find it before.
But some enterprising researchers asked a different question: Why do we find it later? And they have come up with an explanation from the way our brains work:
They found that patterns of neural signals, called traveling brain waves, exist in the visual system of the awake brain and are organized to allow the brain to perceive objects that are faint or otherwise difficult to see.Salk News, “Traveling brain waves help detect hard-to-see objects” at Salk (October 7, 2020)
These waves are called “travelling” waves because you have to catch them when they’re there for you:
“We’ve discovered that faint objects are much more likely to be seen if visualizing the object is timed with the traveling brain waves. The waves actually facilitate perceptual sensitivity, so there are moments in time when you can see things that you otherwise could not,” says Reynolds, senior author of the paper and holder of the Fiona and Sanjay Jha Chair in Neuroscience. “It turns out that these traveling brain waves are an information-gathering process leading to the perception of an object.”Salk News, “Traveling brain waves help detect hard-to-see objects” at Salk (October 7, 2020)
These waves were detected during anesthesia. At one time, researchers assumed that they were an outcome (artifact) of anesthesia. But the most recent study showed that they are part of our brain while it is awake too. New computational techniques allowed the researchers to spot and track these waves:
They found that the brain’s ability to recognize targets was directly related to when and where the traveling brain waves occurred in the visual system: when the traveling waves aligned with the stimulus, the observer could detect the target more easily. These traveling brain waves, which occurred several times per second, were similar to a stadium of sports fans successively standing up and raising their arms, then lowering them and sitting down again. It appears that the visual system is actively sensing the external environment, according to the team.Salk News, “Traveling brain waves help detect hard-to-see objects” at Salk (October 7, 2020)
Part of the picture is that, when we are in the same environment every day, we often only “sort of” see things. When nothing much changes, our visual system fills in most of our environment from memory so we only notice things that are new. This usually works in our favor because the new things are more likely to be of interest than our usual, unchanged background. But sometimes, we are just not “seeing” something that is definitely there right away. That’s where the traveling waves come in to help us.
Other researchers have uncovered some other remarkable facts about vision in recent years, for example:
➤ Our conscious visual perception (what we realize that we are seeing) lies outside the visual cortex of our brain: Contrary to expectations, our visual cortex (in the back of the brain) processes what we literally see. But it is our frontal lobes that tell us what the scene means. It all happens so quickly that we would not notice.
➤ High tech can help the blind begin to see, at least in a limited way. That’s because the human nervous system can work with electronic information. Six totally blind people enjoyed partial restoration of vision via a device that bypasses their damaged optic nerves to feed camera images directly to the brain via electrodes. There is a long way to go but researchers are encouraged by their findings.
➤ Human vision is very different from machine vision, researchers have also discovered. Artificial intelligence (AI) can easily mistake a teapot for a golf ball or a school bus for a garbage truck. That is because thinking about what is seen plays no role in machine vision but it is critical to human vision.
Our vision, it turns out, is a very complex thing, integrated with our experience of life as a whole.
Note: The journal article on traveling brain waves, Davis ZW, Muller L, Martinez-Trujillo J, Sejnowski T, Reynolds JH. Spontaneous travelling cortical waves gate perception in behaving primates. Nature. Published online October 7, 2020:1-5. doi:10.1038/s41586-020-2802-y, is open access if you go here.
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