Given how slowly our brains react to incoming visual information, it should actually be impossible for us to hit a blistering fastball. But we can. That's because, instead of showing us the world as it really is, our brains offer us a glimpse of the future.
Indeed, our innate ability to track fast-moving objects has perplexed neuroscientists for some time now. But as a new study published today (May 8) in Neuron suggests, our brains “push” forward moving objects such that we perceive them as being further ahead in time and space than they really are. Without even knowing it, we're doing a bit of time traveling.
Tracking moving objects
It takes one-tenth of a second for your brain to process what it sees. Now, that might seem like a really short amount of time, but if an object is coming towards you at 120 mph, like a ball from a tennis serve, it will have travelled 15 feet before your brain knows what hit it — perhaps quite literally.
No doubt — if our brains weren’t able to compensate for these perceptual and motor delays, we’d be in all sorts of trouble. Not only would we have problems hitting a fastball or returning a serve, we wouldn’t be able to pick up on the trajectories of fast-moving objects like cars or incoming fists. We’d also have problems moving objects around, or even navigating our bodies at high speeds.
Neuroscientists have offered some possible solutions, like retinotopic mapping, spatiotopic perceptual maps, or combinations of the two. But these theories don’t do a good job explaining how our brains track objects at fine spatial scales, like the changing positions of fast-moving objects.
Prediction mechanism
To figure out what’s going on, Gerrit Maus from UC Berkeley and his colleagues put six volunteers into a functional Magnetic Resonance Imaging (fMRI) scanner. While their brains were scanned, they watched the “flash-drag effect” (see video) — a two-part visual illusion in which brief flashes can be seen in the direction of motion. The illusion makes people see the flashes as part of the moving background, which in turn triggers the prediction mechanism required to compensate for the brain's processing delays.
After looking at the scans, the researchers were able to pinpoint the part of the visual cortex responsible, a region known as V5. This part of the brain, also called MT+, plays a major role in the perception of motion. And as the researchers now know, V5 also performs calculations about where an object is likely to end up.
"The image that hits the eye and then is processed by the brain is not in sync with the real world, but the brain is clever enough to compensate for that," Maus said in a statement. "What we perceive doesn't necessarily have that much to do with the real world, but it is what we need to know to interact with the real world."
Read the entire article in Neuron: “Motion-Dependent Representation of Space in Area MT+.”