New study provides insight into paths of child vision development
There's more than meets the eye when it comes to the development of visual processing by infants, a new UNC Health study suggests.
In the January issue of Nature Neuroscience, researchers at the University of North Carolina School of Medicine considered the cortical areas that helped mice make sense of what they see. To better understand how visual processing works in humans, they built and utilized intrinsic signal optical imaging and two-photon calcium imaging to track visual responses in mice.
"We found that visually driven activity was well correlated among higher visual areas within two distinct subnetworks resembling the dorsal and ventral visual streams," the researchers wrote in the article, "Stream-dependent development of higher visual cortical areas." "Visual response magnitude in dorsal stream areas slowly increased over the first 2 weeks of visual experience.
"By contrast, ventral stream areas exhibited strong responses shortly after eye opening," they said. "Neurons in a dorsal stream area showed little change in their turning sharpness to oriented gratings while those in a ventral system area increased stimulus selectivity and expanded their receptive fields significantly. Together, these findings provide a functional basis for grouping subnetworks of mouse visual areas and revealed stream differences in the development of receptive field properties."
The ventral stream, which starts to work at birth, is critical to detecting forms and recognizing objects. The dorsal stream, for locating objects and motion, requires visual experiences to fully develop.
"Understanding the mechanisms for postnatal visual development as well as interrogating the V1 (primary visual cortex or striate cortex) and HVAs (higher visual areas or extrastriate cortex) circuit deficits in mouse models of these disorders would provide insights into the pathophysiology of these diseases," the researchers said.
Impact on child development
For infants, there is more to learning than just seeing, says Glen Steele, O.D., chair of the AOA's InfantSEE® and Children's Vision Committee. Dr. Steele also is professor of pediatric optometry at Southern College of Optometry in Memphis, Tennessee.
As infants grow and learn from watching their parents, they need to be able to reach out and touch what they see, Dr. Steele says. Baby carriers and car seats are absolutely needed to address safety concerns. But they also need "tummy time," when infants are allowed full movement to engage in an active visual process, he says.
"Movement is critical for advanced learning and understanding," Dr. Steele says. "This is strongly supported in the literature. As you move, you learn to use vision to satisfy curiosity—'I want to get that'—so I learn to move to get to it and explore. If in a carrier and unable to move, an infant doesn't experience necessary movement in order to learn.
"Most children can 'see' the object of attention, but young children need to handle and manipulate the objects—including going to the mouth—in order to fully understand," he adds. "There also should be specified times to get out on their tummy (tummy time) in order to let them learn to explore on their own. Put things out of their reach in order to stimulate development of the concept of self-movement to get to the object.
Limited or reduced visual function, due to congenital cataracts or visual issues following stroke or brain injury, also can hinder development. "Just seeing clearly is not enough," Dr. Steele says. "One must engage the ability to visually direct action to restore function to the level possible."
Passive vs. active development
The new study supports the work of Richard Held and Alan Hein in the renowned "The Kitten Carousel" experiment in 1963, Dr. Steele noted. In the experiment, kittens were attached to a carousel propelled by Kitten A (active). Kitten B (passive) rode in a basket so it could not control movement.
Kitten A learned about its environment through movement.
"They put the (passive) cat in a box that was totally manipulated by another (active) cat," he says. "The cat in the box had no involvement in controlling movements and thus did not learn the actions and the results of his actions. When the cats were removed, the one directing the action carried on like nothing happened. The one in the box had to learn all the actions and movements for the first time."
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