Seeing beyond vision
Studying how we see is changing views of decision-making, autism and neurological disease
The eyes may or may not be a window to the soul, but they are certainly a window to the brain. Several Stanford researchers use vision to understand the basic goings-on inside our heads. Their studies illustrate the range of what vision can teach us about ourselves.
Today William Newsome, PhD, a professor of neurobiology and director of the Stanford Neurosciences Institute, is perhaps best known as one of the founders of the neuroscience of decision-making and its offshoot, neuroeconomics, but he remains well-known for work in his original field, monkey vision.
“The first 20 years of my career was devoted to the study of vision,” Newsome says, “which led naturally into the study of decision mechanisms over the past 20.”
The breakthrough came when Newsome and his lab were studying how monkeys perceive motion. The team would train monkeys to report whether a pattern of dots on a computer screen was, on average, moving up or down, using juice as a reward for correct responses. Meanwhile, they were tracking electrical activity in neurons in the monkeys’ visual cortexes. At first, the idea was to look for simple patterns in that electrical activity that predicted the monkeys’ responses.
“That’s when I realized ‘Hey, we really need to understand how sensory evidence is converted to decisions in the brain.’”
The ensuing research caught the interest of economists seeking a better understanding of decision-making. It had become clear to some economists by the 1970s that some of their core assumptions about how humans choose were not always right. The Newsome lab’s research held the promise of building stronger new assumptions from the ground up, and today decision neuroscience is a major focus of research worldwide. Among other things, the field showed that two brain chemicals, serotonin and dopamine, track the costs and benefits associated with a given choice, and that higher testosterone levels may lead to riskier economic decisions. Decision neuroscience also helped launch more biologically oriented studies of politics, such as a series of studies that linked individuals’ political predispositions to their physiological reactions to uncertainty and disgust.
Hypersensitivity and autism
Anthony Norcia’s main interests lie in the development of three-dimensional vision and the effects of two conditions — amblyopia (better known as lazy eye) and strabismus, or misaligned eyes — on visual development. But in the last few years, his interest in vision has carried him in an entirely different direction: autism.
The connection is simple, although not universally known. People with autism are often more sensitive to loud noises, scratchy clothing tags and bright lights than others.
“Historically, people thought of autism as a social interaction problem, but there were always reports of hypersensitivity,” says Norcia, PhD, a professor of psychology. In the last decade and a half, researchers have started to look more closely, to try to understand the connection.
There are two prominent theories, Norcia says. First, differences in how kids’ brains treat sensory information at a young age could lead to disorders: If something goes wrong with how information is processed, that abnormality could influence brain development and perhaps lead to autism.
A second, related possibility is that the neurons are hyperactive, which could explain why a substantial majority of people with autism also have irregular electrical activity in the brain, as well as a possible link between autism spectrum disorder and epilepsy.
In his own work, Norcia uses electroencephalograms to track electrical activity in kids’ brains while they read or look at pictures, then compares children with and without autism. One such experiment, published in 2014, found children with autism had abnormalities at the very earliest stages of vision processing — which may have downstream consequences for visual perception and thinking.
Eyes on Parkinson’s and stroke
As a clinical neuro-ophthalmologist, Joyce Liao, MD, PhD, approaches the brain through the eyes of her patients, who are typically in their 50s or older and have begun having problems reading. Difficulties sometimes develop gradually, as is the case for people with Parkinson’s disease who have a related eye movement disorder, or they develop suddenly, as can happen to people who’ve had a stroke that results in partial blindness. But even if doctors ascertain the overarching problem, says Liao, the best available treatments fail to adequately address reading and vision disabilities.
“There are so many different areas in the brain that are dedicated to reading effectively that any one of them, if impacted, could affect reading,” Liao says. Without more specific behavioral or neural symptoms, she says, “it’s actually kind of hard to know how to help them.”
Liao has been tackling that problem, starting with a better understanding of the specific causes of reading difficulties stemming from Parkinson’s and stroke. In the former, she says, eye-tracking experiments show that the telltale shakiness of Parkinson’s extends to the eyes, making it difficult for patients to shift their gaze smoothly from one word to the next on a line.
Stroke has a somewhat more surprising impact. When a stroke blinds patients in one eye, they tend to look into the darkness — if they lose vision in the left eye, for example, they tend to use their good eye to look more to the left than the right. Doing so may help recover some visual acuity, but that bias could make reading harder. Normally, our eyes scan a line of text, spending roughly equal amounts of time on the left and right of the line, but vision loss disrupts the usual pattern. Patients with vision loss in one eye will spend more time on one side than the other, ultimately slowing their reading.
The brain mechanisms underlying reading difficulties in Parkinson’s and stroke remain largely unexplored, Liao says, but she hopes to change that, too. To do so, Liao has teamed up with Brian Wandell, PhD, a professor of psychology who has for decades studied the development of vision and reading in young brains, and Michael Kamil, PhD, an emeritus professor of education. Using some of the same techniques that proved successful in the study of reading, eye movement control and higher-order visual abilities, Liao, Wandell and Kamil hope to better understand how the brain — and our ability to read — responds to injury and degeneration.