Pupillometric contributions to deciphering Stroop conflicts.

The Stroop task gives rise to two major conflicts: the task conflict (respond to the color vs. read the word) and the information conflict that can result from the stimulus-response compatibility (SRC; difference between two responses) or from the stimulus-stimulus compatibility (SSC; difference between the two contradictive pieces of information). We conducted a two-to-one Stroop experiment (i.e., two colors are mapped to one response key) and measured reaction time and pupil dilation. The results showed clear evidence for informational conflict composed of both the SRC and SSC. In addition, pupil indications for task conflict appeared earlier than indications for both the SSC and the SRC, in line with the theory regarding task conflict.