Research Report

Cognitive Processing

, Volume 12, Issue 1, pp 13-21

First online:

Open Access This content is freely available online to anyone, anywhere at any time.

Pupillary Stroop effects

  • Bruno LaengAffiliated withDepartment of Psychology, University of Oslo Email author 
  • , Marte ØrboAffiliated withDepartment of Psychology, University of Tromsø
  • , Terje HolmlundAffiliated withDepartment of Clinical Medicine, University of Tromsø
  • , Michele MiozzoAffiliated withDepartment of Experimental Psychology, University of CambridgeDepartment of Cognitive Science, Johns Hopkins University


We recorded the pupil diameters of participants performing the words’ color-naming Stroop task (i.e., naming the color of a word that names a color). Non-color words were used as baseline to firmly establish the effects of semantic relatedness induced by color word distractors. We replicated the classic Stroop effects of color congruency and color incongruency with pupillary diameter recordings: relative to non-color words, pupil diameters increased for color distractors that differed from color responses, while they reduced for color distractors that were identical to color responses. Analyses of the time courses of pupil responses revealed further differences between color-congruent and color-incongruent distractors, with the latter inducing a steep increase of pupil size and the former a relatively lower increase. Consistent with previous findings that have demonstrated that pupil size increases as task demands rise, the present results indicate that pupillometry is a robust measure of Stroop interference, and it represents a valuable addition to the cognitive scientist’s toolbox.


Stroop Pupillometry Cognitive load Attention Semantics