The eyes can reveal a great deal about attention.
Whether you’re taking an exam or guiding a dog across a busy street, the capacity to ignore irrelevant sights and sounds—or to remain alert to potential threats—is essential for effective performance and safety. Recent research at Duke University used monkeys to explore how the brain handles distractions, revealing that changes in pupil size in response to distracting stimuli may be tied to how well the brain maintains focus on a goal.
The findings, published in the journal Neuron, shed light on the neural and physiological mechanisms that support attention. They have implications for understanding conditions in which attentional control breaks down, such as attention deficit hyperactivity disorder (ADHD), and for developing strategies to enhance performance in academic and workplace settings.
Over the past decade, scientists have increasingly recognized that eye behavior—movements and pupil dynamics—carries important information about internal mental states and how the brain regulates attention and arousal. This line of work has inspired practical applications: next-generation vehicles that monitor drivers’ eyes to detect distraction or drowsiness, and clinical approaches that use pupil measures to help assess risk for anxiety or to evaluate responses to treatment.
“Where the eyes go and how much visual information enters the system gives us a window into the brain’s current priorities,” said Michael Platt, director of the Duke Institute for Brain Sciences and the Center for Cognitive Neuroscience.
In the study, Platt and colleagues trained rhesus macaques to shift their gaze to a designated visual target in order to receive a juice reward. While the animals performed this task, the researchers briefly flashed images of other monkeys’ faces on the periphery of the display. Since monkeys are highly attentive to conspecific faces, the peripheral faces acted as potent distractors—especially when those faces conveyed clear emotion.
When a subject must choose between two competing sources of information, the brain engages a conflict-monitoring circuit centered in the dorsal anterior cingulate cortex (dACC). The dACC is part of a broader network that helps regulate cognitive control and emotional responses when task demands conflict with distracting or competing inputs.
Using microelectrodes implanted in the monkeys’ dACC, the team recorded electrical activity from single neurons while the animals performed the gaze task. They discovered a population of neurons that became active specifically when the monkeys were engaged in the task and needed to override the distracting faces. These neurons did not respond simply to the target or to the face alone, but to the conflict between them—a neural signature of the effort to maintain focus.
Finding conflict-sensitive neurons in monkeys was surprising, the authors noted, because earlier studies had searched for such signals without detecting them. That led some researchers to wonder whether conflict signaling was unique to humans. The new results indicate that at least some aspects of conflict monitoring exist in nonhuman primates as well.
Notably, greater activity in these dACC neurons predicted improved performance: monkeys whose conflict-related neuronal activity increased were better able to ignore the distracting faces in subsequent trials. Yet the task remained challenging, and making mistakes or experiencing conflict often produces stress and arousal—responses that can hamper concentration.
“Conflict and errors tend to activate our stress systems, which can disrupt focused behavior,” said R. Becket Ebitz, the study’s first author. The fight-or-flight response triggers the release of noradrenaline and typically causes pupils to dilate, allowing more light—and potentially more information—into the eye.
Interestingly, the researchers observed that the monkeys’ pupils adjusted in ways that correlated with task difficulty. When distractor faces became harder to ignore, the pupils constricted, and smaller pupil size predicted better performance on later trials. In other words, pupil dynamics tracked aspects of attentional control and readiness for future task demands.
Although the study revealed clear correlations among dACC neuronal activity, pupil size, and the animals’ ability to resist distraction, the authors caution that correlation does not prove causation. Further experiments will be necessary to determine whether dACC activity and changes in pupil size directly cause improvements in attentional performance.
The dACC does not directly control the muscles that change pupil size, but it communicates with other brain regions that regulate arousal and autonomic responses. The investigators suggest that the dACC may help keep arousal at an optimal level—temperate enough to avoid panic or distraction but alert enough to support focused behavior.
Platt and colleagues plan to continue exploring how pupil dynamics, attention, and vigilance interact. Hormones and neuromodulators could play an important role: earlier work from the same group showed that inhaled oxytocin, a hormone associated with social bonding, made monkeys better at overriding distracting faces, possibly by exerting calming, focus-promoting effects.
The research was funded by the National Institutes of Health (R01-MH-086712 and R01-MH-089484) and the U.S. Department of Defense (W81XWH-11-1-0584).
Contact: Karl Bates – Duke University
Source: Duke University press release
Image Credit: Lauren Brent/Duke University (adapted from the press release)
Original Research: Ebitz and Platt, “Neuronal Activity in Primate Dorsal Anterior Cingulate Cortex Signals Task Conflict and Predicts Adjustments in Pupil-Linked Arousal,” Neuron. Published online February 4, 2015 (doi:10.1016/j.neuron.2014.12.053).