Data of a classic Stroop task with a simultaneous pupil size measurement.

28 participants performed a Stroop color-naming task with three-word stimuli (Dutch equivalents of blue, green, and red) and three neutral non-word stimuli (“XXXXX,” “SSSSS,” “ZZZZZ”) which were presented in blue, green or red. Equal numbers of incongruent, neutral, and congruent trials were presented in random order. The words were presented until the participant responded, with a maximum duration of 2 s. During the response-to-stimulus interval (RSI), the letter string was replaced by a white fixation point for 3.3 s, allowing the evoked pupil response to return to baseline level before the measurement of baseline pupil diameter on the subsequent trial.