N170 effects during exact and approximate calculation tasks: an ERP study.
Event-related potentials were used to investigate the neural correlates of two-digit exact and approximate addition calculations. The results showed that the dissociation between exact and approximate calculations began at approximately 150 ms after stimulus. In the left hemisphere, N170 amplitude elicited by exact calculation was larger than that elicited by approximate calculation; however, in the right hemisphere, N170 amplitudes elicited by the two calculation strategies were not significantly different. Moreover, a larger P3 amplitude was elicited by exact calculation than by approximate calculation. In the 130-210 ms windows, dipole source analysis of the difference wave (exact calculation minus approximate calculation) indicated that the generator of N170 was localized in the left fusiform gyrus.