"Aha!" effects in a guessing riddle task: an event-related potential study.

Insight problem solving has been the topic of much investigation. It is believed widely that insight critically contains the process of breaking one's mental set. Recent functional magnetic resonance imaging (fMRI) research on puzzle solving showed that insight was associated with activities in anterior cingulate cortex (ACC) and other areas (Luo and Niki [2003]: Hippocampus 13:274-281). We proposed ACC might mediate processes of breaking one's mental set, given its well-known role in cognitive conflict. In the present research, high-density event-related potentials (ERPs) were recorded to examine the electrophysiologic correlates of insight problem solving. One hundred twenty interesting Chinese riddles (half difficult and half easy) were adopted as materials. For each trial, subjects were either given an easy puzzle followed by a keyword that was consistent with the subject's initial thinking ("No-aha answer"), or a difficult puzzle followed by a keyword that was consistent with an unusual interpretation, so that it broke the subject's initial mental set ("Aha answer"). Results from 14 subjects showed that Aha answers elicited a more negative ERP deflection than did No-aha answers in the time window from 250-500 msec after onset of the answer. The ERP difference wave (Aha minus No-aha answer) showed the maximum amplitude over the central site (Cz) with a peak latency of 380 msec (N380). Voltage and current density maps of the difference wave showed strong activity and current density in the frontocentral region. Dipole analysis localized the generator of the N380 in the ACC. N380 therefore probably reflects an "Aha!" effect, and the ACC generator may be involved in the breaking of mental set.