The Stroop's test evokes a negative brain potential, the N400

The Event Related Potential (ERP) of 8 french right handed subjects were recorded with 5 active electrodes located in frontal (Fz), central (Cz), occipital (Oz) and right/left parietal (RH, LH) sites while they were performing a modified version of the test of Stroop. They had either to read the names of basic colors (yellow, green, blue, red) written in the same colors (red written in red: concordant stimuli) or in a different color (red written in blue: discordant stimuli) or to name mentally the color in which was written the name of a color, both colors being concordant or discordant. The ERPs for reading were similar for concordant and discordant stimuli and showed no sign of a N400 wave, this was also the case for the mental naming of a color associated to the written name of the same color. A N400 wave with a Cz location was evident for the mental naming of a color when it was associated to the written name of another color. In this last case, the automatic reading of the name of a color would correspond to a priming which interferes with the access to the target word: the name of another color that the subject is required to evoke mentally.