An Investigation into the Stroop Effect

Categories: ExperimentPsychology

Stroop conducted experiments in the 1930s on interference with visual perception. He discovered that participants had difficulties naming colours when they were printed in different coloured inks.

In some lists, colour words were spelled and printed in the same ink colours (congruous).

Example: RED

In other lists the words and colours did not match (incongruous).

Example: GREEN

Participants in Stroop’s experiments took longer to name the incongruous words. He called this the ‘Stroop effect’.


To investigate the Stroop effect by conducting an experiment to time how long it takes for participants to say the colours of the words on two different lists (congruent/incongruent).

To then produce evidence in the form of graphs and data analysis to support or disprove the following hypothesis.


The average mean time to complete list two (incongruous) will be greater than the average mean time to complete list one (congruous).

IV – lists of words congruent/incongruent

DV – time taken to name ink colours measured in seconds


As quantitative data (time) is being measured, the experiment should be as controlled as possible.

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A field experiment will allow as many of the possible extraneous variables that may affect the DV to be controlled. If these variables are controlled it is more likely that any change in the DV is a result of the IV rather than other confounding variables.

Variables to be Controlled:

* the room in which the experiment is to take place

* time of day

* lighting

* list size (number of colour words)

* font size/colours/background/row column size (all to be standardised to prevent confounding variables)

* no other persons in the room to be present

* English as first language

* reading glasses to be worn

* background noise


A sample of sufficient size to be representative of the population must be chosen, this will be twelve people.

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This number should yield enough data to allow comparisons/calculations to be made. An opportunity sample will be taken. Criteria for participation will be:

* Willingness to participate after briefing

* Adults age 16+

* Either gender

* English as 1st language

* To wear normal reading glasses/contact lenses.

Ethical Considerations

* Consent. Informed consent will be obtained before conducting the experiment.

* Withdrawal. Participants will be told they may withdraw from the experiment at any time during/after the experiment. Data concerning the individual will be destroyed.

* Confidentiality. All participants’ details will be treated confidentially.

* Briefing. Participants will be briefed/debriefed using standardised forms making sure they have all information about the experiment. Participants will be asked if they have any further questions/concerns both before and after the experiment.


* Lists of colour words are typed using Arial font size 22 capitals as standard. One list contains 25 colour words that match the font colour (congruous) ie GREEN. The other list contains 25 colour words that do not match the font colour (incongruous) ie YELLOW. Both lists contain 25 words so data from each list-time can be compared. Lists are standardised (same font/size/paper/colour order) for the same reason.

* A copy of the words is taken so that accuracy can be checked at the time of the experiment.

* Briefing and debriefing information is standardised and typed. This will make sure participants have all the information they need and nothing is forgotten.

* Instructions are standardised, typed and handed to participants to ensure they received the same information in the same order.

* A stopwatch will be used to record times and a table created to record raw data.

* Participants’ details are not recorded; they are replaced by numbers for confidentiality.


1. Member of the target population is asked if they would be willing to participate in an experiment on visual perception.

2. If willing, participant is briefed by handing them the information leaflet.

3. Any questions are answered. Participant is given the opportunity to withdraw at any time. This was written in the briefing information but will be asked verbally as well.

4. Participant is handed list one and asked to quickly but accurately name the colour words NOT READ them. This was timed and recorded in the table of data. List two was then timed in exactly the same manner.

5. Participant is then debriefed and any further questions are answered.

6. Participant is thanked and assured again of the right to withdraw/confidentiality of the experiment.


Raw Data Table:


LIST 1 Congruent time (seconds)

LIST 2 Incongruent time (seconds)





































From the raw data it is easy to see that there is a wide variance in times within both lists and between the two lists. This will be shown more visually in a comparison bar chart.

The bar chart shows that the hypothesis that list two would take longer is correct. Analysing the data shows that the mean average time for lists one and two are as follows:

List one mean average time = 10.08 seconds

List two mean average time = 24.76 seconds

The bar chart also shows that the range of times taken seems to be wider for list two than list one.

List one range = 4.09 seconds

List two range = 17.87 seconds

There is a far wider range for list two than list one. This shows that participants had more difficulty with saying incongruent colour names than congruent ones. The time taken for list one (congruent) seems to bear little relationship to the time taken for list two (incongruent).


* Sample size was quite small. To be more representative of the target population a larger sample would have been preferable.

* Opportunity Sampling was used for this experiment. In this case all participants were office workers who were colleagues. This is not representative of all people and could have affected results.

* Controlling variables a field experiment does not allow total control of all variables that may affect results.

* Participants these were known colleagues, this may have influenced the way they participated in the experiment.

Extending the Experiment

* Would age or gender affect the results? Take a larger random sample of different age/gender ranges and compare the results.

* Change the two lists of words for one list of congruent words and an audiotape with a person speaking colour names on it. This should have the same effect of trying to do two tasks at the same time, listening and naming.

* If the participants were allowed to keep repeating the experiment would the time taken to complete incongruous lists lessen through practise?


Stroop suggested that reading words is an automatic (learned) response. When a person is given a list of words they will read them, even if they have been asked not to. When presented with words and colours that do not match, people will still try to read the word instead of naming the colour. Participants find it difficult to suppress the need to read words. This causes conflict and results in a slower response time.

The results of this experiment seem to support Stroop’s theory. The response times for incongruent lists vary widely. This may be because some participants were less flexible in shifting from one task to another. All participants admitted to reading list one when they found that word and colour matched. This caused great difficulty when word and colour did not match. This would also support the theory that reading is an automatic response.

Cite this page

An Investigation into the Stroop Effect. (2020, Jun 02). Retrieved from

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