This short video summarizes their findings.
Here is the citation and abstract for the paper, which is available in full online.
Fleming, SM, Weil, RS, Nagy, Z, Dolan, RJ, and Rees, G. (2010, Sep 17). Relating Introspective Accuracy to Individual Differences in Brain Structure. Science, 329(5998); 1541-1543. DOI: 10.1126/science.1191883
This article cites 28 articles, 8 of which can be accessed free: http://www.sciencemag.org/content/329/5998/1541.full.html#ref-list-1
The ability to introspect about self-performance is key to human subjective experience, but the neuroanatomical basis of this ability is unknown. Such accurate introspection requires discriminating correct decisions from incorrect ones, a capacity that varies substantially across individuals. We dissociated variation in introspective ability from objective performance in a simple perceptual decision task, allowing us to determine whether this interindividual variability was associated with a distinct neural basis. We show that introspective ability is correlated with gray matter volume in the anterior prefrontal cortex, a region that shows marked evolutionary development in humans. Moreover, interindividual variation in introspective ability is also correlated with white-matter microstructure connected with this area of the prefrontal cortex. Our findings point to a focal neuroanatomical substrate for introspective ability, a substrate distinct from that supporting primary perception.
You can access some of Stephen Fleming's articles at his home page's publications link.