NYU (US) — The relationship between the brain and visual perception varies depending on the type of motion being viewed, a finding that suggests a significantly more complex process than previously thought.
Perception of motion was previously thought to be derived from a relatively simple process—relying on a single cortical area in the brain, the MT, long known to have a well-established role in processing information about moving visual objects.
Less clear is the scope of its influence; does it dictate the ability to detect all types of motion or is its function more limited or, perhaps, more nuanced?
With this in mind, scientists set out to examine how the visual system processes two types of motion: local motion, which involves tracking signals that fall within a small retinal area, and global motion, in which several movements are integrated over larger areas. Specifically, they monitored activity in MT to determine if its neurons were active in response to both types of motion.
In normal scenes, local and global motion are normally in agreement. Here, the researchers conducted experiments in which macaque monkey and human subjects watched specially crafted patterns in which the local and global motion information were in competition. The researchers made physiological and perceptual measurements of brain activity.
The results, published in Current Biology, showed notable differences in how the visual system functions in processing local and global motion. Neuronal activity in MT was controlled by the local motion in the stimulus and unaffected by global motion.
Under the same conditions, though, humans’ perceptual responses were dominated by global motion, which means that their responses were determined by a second brain mechanism that encodes global motion, whose nature is currently unknown.
“While comprehending the specifics of this process requires more work, it’s clear that motion perception does not depend on a single cortical brain area, but, rather, reflects the action and interaction of multiple mechanisms,” says J. Anthony Movshon, director of the Center for Neural Science at New York University and the paper’s senior author.
“We now have new tools to help us identify and study brain systems that are currently unknown.”
The study’s other authors include researchers from NYU, Stanford University, and the University of Washington.
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