As we walk from Point A to Point B, be it from the living room to the kitchen or down a busy street, our eyes take in a great deal of information. Despite our bodies being in motion, we are able to focus on the end destination and navigate to the destination without much of a problem. What mechanisms drive this process? Research conducted at the University of California Berkeley (UC Berkeley) and the National Eye Institute (NEI) suggests that vision and navigation are more intricately linked than previously believed.
Research at the Herbert Wertheim School of Optometry & Vision Science at UC Berkeley found that there are neurons in the eye that are crucial for maintaining a sharp image of the world, while moving from place to place. These neurons form part of the gaze stabilization system. This system works without our conscious awareness and ensures that our eyes to follow the direction where the visual scene is moving, whether one is walking down a street or is looking out a bus window, and helps to maintain a sharp image. This system works with the inner ear vestibular system, which detects the position of our head in space and coordinates eye movement, posture and balance.
Scientists identified a specialized retinal ganglion cell type known as direction-selective ganglion cells (DSGCs). These cells increase activity in response to motion in the visual field when the motion happens in the “preferred” direction. Yet, they aren’t active to motion occurring in the opposite direction. Responses from the neurons tell the gaze stabilization system which direction the visual scene is moving.
This research promises deeper insights into retinal mechanisms, how they contribute to gaze stabilization and how disorders cause unstable gaze, such as nystagmus. Some forms of nystagmus can take place alone or with other eye problems, such as certain inherited retinal disease and could be the result of abnormal DSGC activity in the retina. In addition, this work may lead to creating diagnostic tests that are more sensitive to eye diseases, such as glaucoma, which cause ganglion cell degeneration. For example, if the direction-selective ganglion cells are damaged, changes in eye movements might be a biomarker for early damage.
Yet, how does moving our bodies relate to how visual information is processed? Research at NEI learned that in primates, activity in the part of the brain that manages signals from the eyes, known as the visual cortex, is unaffected by the body’s own movements.
For years, when scientists studied how the brain processes visual information, they overlooked the influence of the animal’s body movements. Yet, an animal interacts with its environment by moving its body. Recently, researchers discovered neural activity in rodents from body movements throughout many areas of the brain, including the visual cortex. While modern technology can account for these signals, earlier studies weren’t able to do so. That means the results from the rodent study challenges the validity of other studies.
A group of NEI scientists lead by Hendrikje Nienborg, PhD, found that in contrast to rodents, movement by primates creates very little neural activity in the visual cortex. Also, the small amount of neural activity that was recorded was due to the changes in visual information from eye movements, not from the movement itself. This shows that previous research visual processing is still valid, despite ignoring the animal’s movements.
These findings expand our understanding of how vision and movement connect with each other. They show the mechanisms within our eyes and brains, revealing how we maintain visual stability while moving from place to place. These discoveries may lead to diagnostic tools and treatments for conditions, such as nystagmus and glaucoma. Vision research projects like those at UC Berkeley and NEI underscore the need for additional work into how visual processing works in real world scenarios.