Stroop Color and Word test is one of the most widely used tests for assessing inhibitory control and selective attention. The past research shows a strong correlation between eye-movements and executive functions, with a conclusion that eye-movements provide a reliable cognitive measure. We used an alternative method of measuring Stroop interference by eye-tracker data collection. Data collected with the eye-tracker contained information about eye fixations, saccades, pupil size and reaction time (RT) in five different contexts including four types of stimuli. Results show that interference in the duration of fixation is a very good predictor of the interference in response RT in the mixed context for all types of stimuli we used. Pupillary responses did not show a statistically significant difference in pupil size while presented with different stimuli types. However, the method used to measure the difference in size in this study was different in comparison to previously published research, thus not allowing us to validly reject conclusions of the previous studies. We confirmed the past findings about the importance of choosing the right type of neutral stimulus when measuring RT and Stroop interference. The effect of interference was bigger when the nonword control stimuli were used for calculating size of interference in the test compared to the usage of verbal control stimuli. Facilitation effect was present only when compared with verbal control stimuli. When compared with nonword control stimuli, the interference effect was observed instead of the facilitation effect. The measure of the fixation durations showed similar results gathered with analysis of the RT. Using fixation duration and saccade measure we show that our participants are capable of processing different information in parallel even when the information presented to the subject are in conflict. Thus, our findings are speaking in favour of the theoretical parallel distributed processing model.
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