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How the Eyes & Brain Work Together Regarding Recognition & Memory

Posted by Ilena Di Toro | Posted on September 26, 2023

It has been said that the eyes are the front of the brain and considering how up to 80 percent of what we know comes via vision, it is important that they are both in working order. How does the brain work when it comes to memory and perception. What about after a traumatic injury? What happens to brain and vision then? Well, there are two studies that looked into those things and here are what scientists found out.

Where Have I Seen This Before?
There is a difference in brain processing between seeing something for the first time versus remembering what was once seen. A study done at New York University showed how different they are.

It was previously thought that recalling what we have seen meant reactivating the same neuronal process that was used when the item in question was seen for the first time. Yet, the relationship between vision and memory was unclear. To learn more about this, researchers did some experiments with human subjects using functional MRI (fMRI). They measured the subjects’ visual cortex responses as they viewed simple geometric shapes in different locations on a computer screen. Later the subjects were asked to recall the make-up of the objects. The researchers changed location of the objects in the course of the experiment in order to monitor and understand memory activity in the visual system in a very precise way.

While the results showed similarities between neuronal activity when processing the shapes and asked to recall them, what differed during memory also differed during perception. These differences came about from how the scenes are mapped onto the brain. Researchers found that during perception, viewing an object activated a small part of the primary visual cortex. Next, it activated a larger part of the secondary visual cortex and after that it activated larger parts of the higher cortices. This was expected due to the known properties of the visual hierarchy. What wasn’t expected was how the progression is lost when recalling a memory. This loss of progression during memory might explain why remembering a scene is different from seeing one and why there is less detail available in memory.

Half a Brain Works
Have you ever met someone who didn’t seem very bright and think “That person only has half a brain.” After reading this, you might think differently about using that term.

A study done at the University of Pittsburgh looked into the brain plasticity and visual perception of those, who as children, had surgery whereby half of their brain was removed. The question researchers wanted to answer was whether the brain is prewired with its capabilities from birth or if it can organize its functions as it matures.

The brain halves, known as hemispheres, have two definitive responsibilities. The left hemisphere is the region of the brain that handles reading printed words. The right hemisphere is the region of the brain that recognizes faces. There are limits to the brain’s neuroplasticity and over time the hemispheric preferences become rigid. In cases where someone develops a brain lesion because of a stroke or tumor, that person may develop a reading impairment or become face blind, depending on whether the right or left hemisphere is affected. What happens when the brain is forced to change while it is more malleable?

Researchers looked at a group of patients who had a surgical removal of one hemisphere to control epileptic seizures. While this kind of surgery is rare, thanks to telemedicine, researchers were able to enroll 40 hemispherectomy patients in the study.To test word recognition, the researchers presented the subjects with pairs of words that differed by one letter, such as soup and soap. To test face recognition, researchers showed subjects pairs of photos of people. Each image appeared on a screen for only a fraction of a second and subjects had to decide whether the pair of words or faces were the same or different.

As it turned out, the remaining hemisphere was able to maintain these functions. The difference between those who had the hemispherectomy and the control group was less than 10 percent. In fact, the average accuracy was above 80 percent. That means losing half a brain doesn’t mean losing half of its functionality.

Once again, research is showing how the eye and brain work together to create vision.


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