Despite these limitations, pupillometry is a valuable tool for psychological research, says Pittsburgh's Steinhauer, because our eyes are easy to observe as well as provide a sensitive indicator of cognitive, emotional and sensory response. "It's like having an electrode permanently implanted in the brain," he says. "And all we can do is watch the change at the end. We can't monitor everything going into it."
This article is provided by Scienceline, a project of New York University's Science, Health and Environmental Reporting Program.