The Eyes Have It
Though there is no consensus about which of our five senses is the most important, sight has an edge. Philosophers from Aristotle to Galileo have exalted vision above other sensory capacities, tying it to humanity’s noblest pursuits. From a neuroscientific perspective, visual processing is the most dominant sensory function in the brain. And culturally speaking, most Americans believe there could be no health outcome worse than losing their eyesight.
The perceived value of sight is reinforced by the fiercely visual nature of contemporary life. Screens are now constantly at our fingertips. They saturate us with visual information to process, and the remote social interactions they facilitate are devoid of embodied inputs like smell and touch.
Our sense of sight confers power. We use it to investigate and surveil the planet (and beyond) and take pleasure in its splendors. But sight is also a source of vulnerability. The biological processes that allow our visual system to observe the world accurately can also lead us to perceive illusions — and we don’t always know the difference.
Brain game
Sight begins in the eye. Light passes through the dome-shaped cornea and enters the eye’s interior through the opening called the pupil. The iris (the colored part of the eye) controls how much light the pupil lets in. Next, light passes through the lens, the clear, inner part of the eye that focuses light on the retina. This light-sensitive layer of tissue at the back of the eye contains special cells called photoreceptors that turn the light into electrical signals.
Yet even as the eye receives visual input, “seeing” actually happens in the brain. Electrical signals travel from the retina through the optic nerve to the occipital lobe, an area toward the back of the brain that contains the visual cortex. Half of the brain then becomes involved, directly or indirectly, in interpreting the signals.
There’s quite a lot that needs interpreting. Light passing through the eye is bent twice — first by the cornea, then by the lens. This double bending means that whatever you’re looking at appears upside down on your retina. Your brain makes sure you perceive it as right-side up. Likewise, you perpetually receive two images of the world, one through each eye, and your brain combines them into one.
The role of the brain in sight is most apparent when we’re confronted with visual stimuli that are ambiguous. For example, the “impossible” staircase in M. C. Escher’s Ascending and Descending appears to climb up and down simultaneously because, as your brain attempts to translate the 2D image into 3D reality, it falls back on assumptions that lines are straight and corners are 90 degrees.
Perhaps you remember the bad cellphone photo of “the dress” that went viral in 2015? Some insisted the dress was white and gold; others swore it was black and blue. Research revealed that people’s life experiences influenced their color perception.
Night owls were more likely to see the dress as black and blue, whereas early risers tended to see it as white and gold. That may be because of assumptions each group made about whether the garment appeared in bright daylight or under an indoor bulb — a difference of illumination that cues our visual system toward divergent color interpretations. Those who burn the midnight oil were more inclined to assume artificial lighting than those who rise with the sun, perhaps because of more exposure to it.
“We rely so much on our sense of sight that we trust what we see with our own eyes,” says USC Dornsife’s Norbert Schwarz, Provost Professor of Psychology and Marketing. “Seeing is believing, as the saying goes. But our visual processing can be fallible.”
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Making accurate visual judgments is a core part of human survival. We evolved to rely on sight for orienting ourselves to our environment, avoiding danger and navigating through space. Jennifer Bernstein, a visiting scholar at the USC Dornsife Spatial Sciences Institute, notes that all cultures have developed practices for wayfinding, which involves figuring out where you are and how to get where you need to go.
When technology “sees” the path for us, our sense of sight is no longer just a tool of survival — it’s a window into pleasure.
Inuit hunters in the Canadian Arctic provide an example of how sharply developed our visual perception can become in the service of wayfinding. Amid the snowy landscapes of the Igloolik region, few topographical landmarks stand out to differentiate routes. Young Inuit learn through years of tutoring by elders to orient themselves by attending to visual cues as subtle as snowdrift shape and wind direction. Amazingly, up until the recent adoption of GPS devices, the Inuit had no concept of being “lost.”
If you’ve ever felt directionally challenged without your mapping app — or gotten lost even while using one — you’re probably aware that digital tools are eroding our visual attentiveness to navigational cues in the landscapes we traverse. Bernstein points to research linking GPS use to lower spatial cognition and poorer wayfinding skills.
But she cautions against demonizing the technology, arguing that GPS tools can function as visual “prostheses” that augment our powers of sight. GPS can help those with visual or spatial impairments navigate the world independently. For sighted individuals, mapping apps can facilitate a shift in visual attention from the “how” of navigation to an appreciation of the sights along the route.
“If I can just get in the car and drive, I can look at the fog and the Golden Gate Bridge,” says Bernstein of letting GPS guide her around the Bay Area. In other words, when technology “sees” the path for us, our sense of sight is no longer just a tool of survival — it’s a window into pleasure.
Chasing beauty
Our visual system is designed for delight. The neural pathway that extends from the retina to the occipital cortex contains opioid receptors, which, when activated, trigger a cascade of chemical changes linked to feelings of pleasure.
The late Irving Biederman, Harold Dornsife Chair in Neurosciences, and professor of psychology and computer science, and director of USC Dornsife’s Image Understanding Laboratory, explained this neural system in a previous issue of USC Dornsife Magazine. “When [our eyes] are not engaged in a deliberate search, such as looking for our car in a parking lot,” he said, “they are directed towards entities that will give us more opioid activity.”
Gazing at beautiful things — natural vistas, compelling artworks, attractive people — stimulates our brain’s reward system and makes us feel good. But the old adage is also true: Beauty is in the eye of the beholder.
According to Schwarz, individuals develop an aesthetic preference for visual stimuli that they find easy to process. In one of Schwarz’s experiments, subjects were given a list of words to learn. In one group, the word “snow” was on the list; in the other, the word “key” was featured. Both groups were then shown pictures of a snow shovel and a door with a lock. Those in the “snow” group rated the shovel as prettier; those in the “key” group rated the door as more attractive.
“Any variable that makes processing easier increases perceived beauty, even if it’s a variable that has nothing to do with beauty,” says Schwarz.
In addition to neurochemical and cognitive factors, cultural norms also influence what we see as beautiful.
When viewing paintings or sculptures, we often prize the sophistication of an artist’s vision — a sort of “inner eye” that interprets what it sees in a unique way. But USC Dornsife’s Kate Flint, Provost Professor of Art History and English, explains that artistic and social norms of each era influence both the creation and reception of art.
“Beauty in a work of art … is incredibly culturally determined,” she says. “There are conventions of what constitutes the beautiful at certain times, which then get upended by other generations, other traditions.”
See for yourself
Romantic poet William Blake once mused on the possibility of seeing a world in a grain of sand. He was alluding to not only the grandeur but also the knowledge we can access with our powers of sight — if we pay close enough attention.
Of course, with the naked eye, we can’t actually see the (microscopic) world in a grain of sand or, for that matter, the (telescopic) world in a speck of celestial light. Our desire to know and understand truths beyond our visual limits has driven the development of increasingly powerful sight-enhancing technologies.
State-of-the-art telescopes have offered astrophysicists like USC Dornsife Dean Amber D. Miller the opportunity to visualize faraway stars and look back in time. The first images released from NASA’s James Webb Space Telescope earlier this year revealed the presence of never-before-seen galaxies, whose light originated more than 13 billion years ago — around the time of the Big Bang. Miller has likened such images to “‘baby pictures’ of the cosmos.”
Much closer to home, USC Dornsife scientists are making profound leaps in microscopy. At the USC Michelson Center for Convergent Bioscience, the cryo-electron microscopy core facility that opened last year is enabling researchers to glimpse molecules as tiny as individual proteins. And the Translational Imaging Center (TIC), based at USC Dornsife and USC Viterbi School of Engineering, is at the forefront of developing new tools that enable scientists to watch the biological processes of cells as they are unfolding — building microscopes that can collect technicolor images with a speed and sensitivity once thought impossible. TIC researchers can watch the circuit changes in the brain that accompany learning down to the single synapse level. Their collaborators at Keck School of Medicine of USC, Brian Applegate and John Oghalai, are even able to observe and measure the nanometer-sized movements in the human cochlea, part of the inner ear, as it converts sound to neuronal signals.
These technological advances are making it possible for biologists to see the eye itself in impactful new ways. Scott Fraser, Provost Professor of Biological Sciences, Biomedical Engineering, Physiology and Biophysics, Stem Cell Biology and Regenerative Medicine, Pediatrics, Radiology, Ophthamology, and Quantitative and Computational Biology, directs the TIC. He and his team have been able to peer into an animal’s eye as it takes shape and forms connections in the brain. Recently, Fraser and his team have turned their tools to the human eye, observing the changes wrought by age and disease. Their hope is that better understanding the eye’s cellular processes can lead to new treatments for vision-robbing diseases like macular degeneration and diabetic retinopathy.
Fraser’s research captures the fragility of sight and its strength all at once. Our eyes may be susceptible to a host of pathologies, but they also have the potential to bring clarity to life’s greatest mysteries.
Illustrations by Egle Plytnikaite for USC Dornsife Magazine