When answering a question, your accuracy in assessing whether you have gotten the answer right—or wrong—might depend on the volume of gray matter in a certain part of your brain, according to a new study.
Introspection—or metacognition, self-awareness about one's thinking—is a high-level mental process. "Accurate introspection requires discriminating correct decisions from incorrect ones, a capacity that varies substantially across individuals," researchers behind the new findings explained in their study.
For the study, researchers used simple visual stimuli to test 32 healthy subjects' perception—and how confident they felt about their assessment of a geometric image. The tests were customized to each individual's level of perceptual skill, in order to keep each subject's accuracy score at 71 percent, so that the test was consistently difficult for all subjects.
"Someone who has good introspective ability will accurately be able to know" if they were correct in their assessment of an image, explains Steven Fleming, a cognitive neuroscientist at the Wellcome Trust Centre for Neuroimaging at University College London and co-author of the new study.
The study team found "considerable variation" in subjects' accuracy in assessing their own evaluations of the images, which was to be expected based on previous research. Fleming and his colleagues used magnetic resonance imaging (MRI) to evaluate the subjects' whole brains for differences in structure and composition in order to look for correlations with introspective ability.
Test subjects' accuracy in assessing their own performance "was significantly correlated with gray-matter volume" in the right anterior prefrontal cortex, the team wrote in their study report, published online September 16 in Science. Subjects with more accurate introspective assessments also tended to have denser connections between that area of gray matter and the axon-filled white matter that connected it.
"We were surprised that we could find differences in the structure in this region that were linked to something high-level like introspective ability," Fleming says.
The difference in gray-matter volume might help clarify the extent to which a person's confidence about his or her introspective abilities is supported. For instance, consider this scenario: Two people see the same scene but quickly come to very different conclusions about the details of what they saw—with both individuals stubbornly clinging to their own judgment even if only one is correct. A third witness might consider his or her own interpretation more deeply but still not be entirely sure that it is correct. Should we trust the most confident witness? Typically, we do. On a day-to-day basis, "we believe that judgments made with high confidence are more accurate," Hakwan Lau and Brian Maniscalco, both of the psychology department at Columbia University and not involved in the new research, wrote in a companion essay in the same issue of Science. "This correlation between confidence and accuracy, although often true, unfortunately is not infallible," they noted.
The new findings bear indirectly on this: An MRI might be able to predict the validity of a person's assessment of his or her own judgments by examining the volume of gray matter in this region. "If you scanned someone's brain, and they show very low gray-matter density in the prefrontal cortex, when they say they are very sure of something, you may not want to take their confidence too seriously," Lau notes.
The brain region tied to metacognition in this study is located behind the eyes; and even though the test itself was based on visual perception, Fleming points out that the anterior prefrontal cortex has been associated with top-level processing abilities that are thought to set humans apart from other animals. Nonhuman brains seem to be less developed in this region. Other researchers see the new finding as a way to investigate the metacognitive abilities of other than healthy adult subjects. "Other animals [and] children have less developed prefrontal cort[ices]," Lau says. "So we may want to test if they are less good in this kind of introspection task." Some animals in studies, he and Maniscalco pointed out in their essay, seemed to be more eager to opt out of tests in which they had low accuracy rates, "as if they were expressing 'uncertainty,'" having engaged in at least some introspection.