In baseball, much is made of the half-second or less a batter is given to swing or not swing at each 100-mph fastball. But another important snap decision is made by the home plate umpire, who must pinpoint the position of the ball as it crosses the plate and immediately decide whether it counted as a ball or a strike. To complicate matters, the strike zone changes size depending on the hitter, pitchers throw balls at varying speeds and with knee-buckling spin, and a good number of pitches fall into a gray zone on the “corners” of the strike zone. Given the hundreds of ejections each year resulting from players arguing balls and strikes with the umpire, the competitive stakes for this task is incredibly high.
Fortunately, the human brain is quite accomplished at rapidly sorting visual information into categories. Even if you’ve never stood behind home plate to call a game, you have experienced this ability. Imagine you are crossing a street, and from the corner of your eye you see a quickly moving object heading your way. From even the most basic of visual features, your brain can quickly categorize a four-wheeled vehicle of any make and model as a “car”…or “thing that will cause me serious harm if I don’t jump out of the way.” Nobody is born with the innate ability to recognize an automobile, but the collected experience of life reinforces the rules of what is a car and what isn’t — as well as complicated sub-categories such as sportscars and SUVs — and keeps them in the brain for rapid retrieval.
The laboratory of David Freedman, assistant professor of neurobiology at the University of Chicago, is interested in where exactly these categories are stored in the brain. For over a decade, Freedman has conducted experiments looking for the brain area that is the earliest responder when an individual must quickly categorize a stimulus.
“Making effective decisions and evaluating every situation that you’re in moment by moment is critical for successful behavior,” Freedman said. “We’re really interested in what changes occur in the brain to allow you to recognize not just the features of a stimulus, but what it is and what it means.”
Typically, these studies are done using monkeys who are taught to play a simple video game while researchers record brain activity from different regions looking for the signals that underlie decision-making, called category signals. In a study published in Science in 2001, Freedman and colleagues at MIT found the first evidence for brain category signals in a region called the prefrontal cortex (PFC). The site made sense, as the PFC (an area that is especially large in humans) has long been associated with complex, cognitive functions such as memory, planning, and decision-making.
However, the trail didn’t end with that finding. Freedman moved on to study another part of the brain, called the parietal cortex, which is located on the sides of the brain and thought to be involved in processing sensory information. By happy accident, Freedman discovered that the parietal cortex also responded while the monkeys played the categorization task, and the signals looked as though they might be even stronger than those seen previously in the PFC. But to determine which of the two brain areas was the original source of category signals, a direct comparison was needed.
That comparison, published this week in Nature Neuroscience by Freedman and graduate student Sruthi Swaminathan, offers the best evidence to date that the parietal cortex is the primary residence for visual categories in the brain. As monkeys played their categorization game, deciding whether two groups of moving dots fell into the same category or different categories, a sub-region of parietal cortex known as the lateral intraparietal areas (LIP) reacted faster and more strongly.
“This is as close as we’ve come to the source of these abstract signals,” Freedman said. “The relative timing of signals in the two brain areas gives us an important clue about their roles in solving the categorization task. Since category information appeared earlier in parietal cortex than prefrontal cortex, it suggests that parietal cortex might be more involved in the visual categorization process, at least during this task,” Freedman said.
In another experiment, the researchers threw their subjects a category curveball. The monkeys were shown an ambiguous set of moving dots on the border between the two learned categories, then asked to compare them with a second set of non-ambiguous dots — a test with no correct answer, akin to an umpire’s borderline pitch. The subjects were required to make a decision about which category the ambiguous stimuli belonged to, and once again LIP neurons corresponded to that decision more closely than PFC.
“During the decision process, parietal cortex activity is not just correlated — it even predicts ahead of time what the monkey will tell you,” Swaminathan said. “You can record neuronal activity in parietal cortex and, in many cases, predict with great reliability what the monkey will report.”
Due to technical hurdles, running the same experiments in actual baseball umpires would be very difficult. But the underlying principle is likely the same in his gamer monkeys and MLB’s Men in Blue, he said: “It’s an interesting learned behavior that’s highly critical for an individual to perform with great reliability, and it’s a spatial categorization with a sharp boundary, so we think it’s the same process.” Studying how those categories are learned and stored in the brain is one of the laboratory’s next goals, with the long-term aim of understanding more about how the brain organizes the busy world into useful groups…and perhaps even how to improve that process.
“The number of decisions we make per minute is remarkable,” Freedman said. “Understanding that process from a basic physiological perspective is bound to lead to ways to improve the process and to help people make better decisions. This is particularly important for patients suffering from neurological illnesses, brain injuries or mental illness that affect decision making.”
Swaminathan, S., & Freedman, D. (2012). Preferential encoding of visual categories in parietal cortex compared with prefrontal cortex Nature Neuroscience DOI: 10.1038/nn.3016