The Stroop effect
Measure how much the meaning of a written word slows you down when you have to name the colour of the ink it is printed in.
Method
Procedure
- A cross appears, then a colour word such as RED, printed in red, green, blue or yellow ink.
- Respond to the colour of the ink, not to the word.
- On half of the 32 trials the word and the ink match (RED in red); on the other half they differ (RED in blue).
- Each word stays on the screen until you respond, or for up to 3 seconds.
Responses
- R
- red ink
- G
- green ink
- B
- blue ink
- Y
- yellow ink
- Touch
- the four colour buttons
Measures
The time from the appearance of the word to your response, and whether the response was correct. Your result compares the median reaction time on matching (congruent) and mismatching (incongruent) trials. The difference, the Stroop effect, estimates how strongly the automatic reading of the word interferes with naming the ink colour.
Practice
Six practice trials, three matching and three mismatching, tell you after each trial what the ink colour was.
The task relies on colour, so it may not work as intended for people with a colour-vision difference.
Terms
- Congruent and incongruent: Congruent: the word and the ink colour match. Incongruent: they differ.
- Interference: Slowing or errors caused by information that is irrelevant to the task but processed anyway.
- Stroop effect: The difference in reaction time between incongruent and congruent trials.
- Executive function: The processes that keep behaviour on track towards a goal, such as setting aside a habitual response.
- Frontal lobe: The front part of the cerebral cortex, involved in planning and in the control of behaviour.
Experiment
Responses stay in this browser tab. Nothing is stored or sent, and everything is lost when the page is closed or reloaded.
Results
Interpretation
A positive difference means that mismatching words slowed you down: the word was read even though you tried to ignore it. Look at the errors too. Interference can also appear as more errors on mismatching trials, most often pressing the key for the word instead of the ink.
Comparison with published studies
Slower responses to mismatching words are among the most consistently reproduced findings in psychology; MacLeod (1991) reviewed half a century of studies of the effect. Stroop (1935) timed people naming colours aloud from whole cards, so his times cannot be compared directly with single key presses.
Limitations
Sixteen trials of each type is few, so the size of the effect can vary considerably between runs. Responding with keys rather than aloud, as in the original studies, also changes the task. Screen colours differ between devices, and the task may not work as intended for people with a colour-vision difference.
The result comes from one person in one session, on a device whose timing and display are not calibrated. It describes this run, not a stable characteristic of the participant, and a second run could differ by chance alone. Research studies test many participants under controlled conditions and report the average with its variability. The experiment is educational; it is not a test of ability or health.
One row per trial: the word, the ink colour, the trial type, your response, reaction time, whether it was correct and whether it was used in the medians (correct and slower than 150 ms). In the file, 1 means yes and 0 means no. The file is created on this device and can be opened in a spreadsheet.
Background
Original findings
Stroop (1935) showed that naming the ink colour takes longer when the word names a different colour. Reading is so practised that the meaning of a word is processed even when it is irrelevant, and it competes with the correct response. The effect has been studied extensively since and remains a standard measure of attention and cognitive control (MacLeod, 1991).
Neural basis
Brain-imaging studies link the conflict between the word and the ink colour to the anterior cingulate cortex, on the inner surface of the frontal lobe (Pardo et al., 1990).
References
- Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 18(6), 643–662. https://doi.org/10.1037/h0054651
- MacLeod, C. M. (1991). Half a century of research on the Stroop effect: an integrative review. Psychological Bulletin, 109(2), 163–203. https://doi.org/10.1037/0033-2909.109.2.163
- Pardo, J. V., Pardo, P. J., Janer, K. W., & Raichle, M. E. (1990). The anterior cingulate cortex mediates processing selection in the Stroop attentional conflict paradigm. Proceedings of the National Academy of Sciences of the USA, 87(1), 256–259. https://doi.org/10.1073/pnas.87.1.256
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