In Review

How can we tell where one object ends and another begins—especially in the dark?

Researchers previously believed contrast sensitivity function—the minimum level of black and white that a person needs to detect a pattern—was mainly dictated by the optics of the eye and processing in the brain.

Now, in a study published in the journal eLife, Michele Rucci, a professor of brain and cognitive sciences at Rochester, and his colleagues explain another factor at play: contrast sensitivity also depends on small eye movements that we’re not even aware of making.

When we fix our eyes on a single point, the world may appear stable, but at the microscopic level, our eyes are constantly jittering. These small eye movements, once thought to be inconsequential, are critical to the visual system in helping us reconstruct a scene.

“Some scientists believed that because they are so small, the eye movements might not have much impact,” says Rucci. “But compared to the size of the photoreceptors on the retina, they are huge, and they are changing the input on the retina.”

By looking at contrast sensitivity, Rucci has found that the movements play a much larger role in our visual system than previously believed.

He likens that system to our sense of touch. To glean information about the surface of a solid object, we rely on a sensory process (the tactile receptors in our fingers) and a motor process (the way we move our fingertips). Similarly, our ability to visually distinguish one object from another relies on the interaction between a sensory process, involving neurons, and a motor process consisting of the small eye movements.

“Vision isn’t just taking an image and processing it via neurons,” says Rucci. “We see because our eyes are always moving, even if we don’t know it.”

Now researchers will be able to incorporate the new research into models of human vision, providing more accuracy in understanding exactly how the visual system processes information—and what can go wrong when it fails.

—Lindsey Valich

A Silver Lining for Amazon Also-rans

When Amazon announced the locations for its new headquarters last November, 18 semifinalist cities breathed a sigh of disappointment—or relief, for those who worried about increased congestion and soaring housing prices.

But according to Simon Business School doctoral student Zhao Jin, there’s some good news for cities that may have been disappointed by the decision. Jin studied entrepreneurial activity in the 20 semifinalist cities both before and after Amazon announced the list, and found a notable uptick in certain kinds of entrepreneurial activity following the announcement.

According to Jin, the results suggest that “the mere possibility of a large company entering a market encourages entrepreneurs to find profitable ways to be useful to that company.”

Assistant Professor Michael Gofman, who supervised Jin’s research, says the paper addresses a fundamental question.

“As Amazon, Apple, Facebook, Alphabet, Microsoft, and other tech giants increase their investment in internal R&D and attract the best talent, some have argued that it discourages startups. Zhao shows that big tech firms actually foster the establishment of startups.”

But will the startups in those cities remain there? “I certainly don’t expect all of them to move or close up,” says Jin. “They knew the risks when they founded their companies and are likely to continue operations.”

The paper, entitled “How Do Large Companies Affect Entrepreneurial Entry: Evidence From Amazon HQ2,” is published online by the Social Science Research Network. —Peter Iglinski

Why High Blood Pressure May Lead to Alzheimer’s

In 2012, Maiken Nedergaard, codirector of the University’s Center for Translational Neuromedicine, made the pathbreaking discovery that the brain had its own waste removal system. She’s since shown that the system is more active while we sleep, can be damaged by stroke and trauma, and can also be harnessed to deliver therapeutics to the brain.

To describe the dynamics of the so-called glymphatic system, Nedergaard has been assisted by Douglas Kelley, an assistant professor of mechanical engineering in the Hajim School and an expert in fluid dynamics. Collaborative research by Nedergaard and Kelley has found that the glymphatic system—which pumps cerebrospinal fluid into brain tissue to flush away waste—is driven by the pulsations of adjoining arteries, and that changes in the pulsations caused by high blood pressure slows the removal of waste.

The research, reported in Nature Communications, might explain the association between high blood pressure and Alzheimer’s disease. Alzheimer’s is characterized by abnormal clumps (amyloid plaques) and tangled bundles of fibers (tau tangles) in the brain.

Artery walls “have to flex harder in order to hold the same shape when there’s more pressure inside,” Kelley says. “And that changes the waveform of the flexing of the artery wall.”

The collaboration between the two labs is part of a $3.2 million National Institute on Aging grant.

—Bob Marcotte

Nurse Practitioners Critical to Primary Care

A growing number of nurse practitioners are providing primary care in low-income and rural areas where physician supply is low, according to a study by School of Nursing researchers published in the Journal of the American Medical Association.

The researchers examined data trends in 50 states and Washington, D.C., from 2010 to 2016, and charted a narrowing gap between the supply of primary care nurse practitioners and physicians, particularly in low-income and rural communities. While previous studies have shown that primary care NPs have a higher propensity to practice in low-income and rural areas than primary care physicians, the Rochester study is the first to examine the breakdown and distribution of the supply of primary care clinicians in relation to income and population density.

“This paper is really sending a message from a policy perspective about how to more effectively use NPs in primary care delivery,” says Ying Xue, an associate professor at the School of Nursing and the paper’s lead author. “It may be most beneficial in looking at how to further structure the entire primary care workforce and how to mobilize all primary care clinicians in order to maximize timely access to care for populations in need.”

—Patrick Broadwater

Is a Widely Used Assessment Biased?

A psychological test performed routinely and recommended by the National Institute for Mental Health contains racial and other biases, according to researchers at Rochester and Harvard. The study is published in Psychological Medicine.

Psychologists use the phrase “mental state understanding” to describe the ability to decipher and infer the hidden emotions and intentions of others. The Reading the Mind in the Eyes Task (RMET) requires participants to view a series of black-and-white photographs, originally from magazines and cropped to include only the eyes of female and male actors.

But the subjects in the photographs are all Caucasian. And participants are asked which of four adjectives—panicked, incredulous, despondent, or interested—best describes the mental state expressed in the eyes (the correct answer has been generated through consensus ratings).

The test is “biased against the less educated, the less intelligent, and against ethnic and racial minorities,” says lead author David Dodell-Feder, an assistant professor of psychology at Rochester. “It relies too heavily on a person’s vocabulary, intelligence, and culturally biased stimuli.”

What surprised the researchers most was that the difference in the performance of people of some races and certain levels of education was as large or even larger than the difference between people with schizophrenia or autism—two groups who exhibit well-documented marked and pervasive social difficulties—and people without those conditions.

One remedy, says Dodell-Feder, would be to keep the design of the task but use stimuli that are multiracial and include different response options.

“Either way, our findings show that it might be premature for NIMH to make strong recommendations regarding the use of certain tasks for measuring mental state understanding before we can thoroughly assess the validity of their usage across peoples,” says Dodell-Feder.

—Sandra Knispel