June 20, 2011
‘Rewarding’ objects can’t be ignored, JHU neuroscientist finds
The world is a dazzling array of people, objects, sounds, smells and events—far too much for us to fully experience at any moment. So our attention is either automatically snagged by something startling, such as a slamming door, or deliberately focused on something important to us right then, such as locating our child among the hordes on the playground. We also know we are hard-wired to seek out and pay attention to things that are rewarding, such as food when we are hungry, or water when we are thirsty.
So what happens when the things that signify a “reward” are actually not important at all? Are they still powerful enough to capture our attention, when so many other things are competing for it?
According to a team of neuroscientists at Johns Hopkins, the answer is yes, especially when those things previously have been associated with something rewarding, such as money. In a paper recently published in the Proceedings of the National Academy of Sciences, a team led by Steven Yantis of the Department of Psychological and Brain Sciences found that test subjects completing a visual-search task were distracted when items that had previously been associated with small amounts of money occasionally appeared.
The results have implications for understanding how the brain responds to rewarding stimuli and may therefore contribute to the development of more-effective treatments for drug addiction, obesity and ADHD, said Yantis, professor and chair of Psychological and Brain Sciences in the Krieger School of Arts and Sciences.
“We know that not everyone who takes drugs becomes addicted to them, but we also recognize that there is some connection between the euphoria that the drugs cause and how that sensation ‘rewires’ the brain in ways that make it difficult to suppress the craving to experience that again,” he said. “One aspect of this scenario is how reward-related objects capture attention automatically in the way that a sign advertising happy hour at a bar might snag the attention of a recovering alcoholic. Understanding the psychological and brain mechanisms of that reward-object pairing, and why some people are more susceptible to it than others, could lead to more-effective treatments.”
In the study, people first searched for red or green circles in an array of different-colored circles displayed on a computer screen. One color was always followed by a monetary reward (10 cents) and the other by a smaller reward (1 cent). After doing this task for more than an hour, the subjects were asked to search for particular shapes (for instance, a circle among diamonds), and color was no longer relevant or rewarded. Occasionally, one item displayed was red or green, and when that happened, the subjects’ responses slowed down, even though they had been instructed to ignore those items, and the items were inconspicuous and had no relevance to the task at hand.
“It was clear to us that those red or green items had become valuable to the study subjects because they were linked in their minds with a reward,” Yantis said.
In addition, the study subjects completed a questionnaire measuring impulsivity. The team found that people who were more impulsive to begin with were even more prone to being distracted by the “high value” red or green objects.
“One measure of good cognitive control is how long a person can hold information in his or her short-term memory, and we found that those people who were less impulsive tended to be more resistant to distraction by those things that had no value in and of themselves but had become associated with a reward,” Yantis said. “We also found that the distraction caused by value-related features persists for weeks after the original learning.”
The team is now investigating how value is learned, and how learned value can seize the brain’s attention circuits, Yantis said.
“We think that this form of attentional capture may play a role in various clinical syndromes like drug addiction,” he said.
The study was funded by the National Institutes of Health and was co-authored by Brian Anderson, a graduate student, and Patryk Laurent, a postdoctoral student.
The article is available online.