IB Psychology Standard Level

Internal Assessment

– The Stroop Effect –

The Effect of Interfering Colour Stimuli Upon Reading Names of Colours Serially

February 2010


This experiment, a partial duplication of the work of Stroop (1935), aimed to demonstrate the cognitive interference caused by conflicting stimuli, as measured by delayed reaction times in participants asked to read a list of words and name the colour of the words (using incongruent colour-word pairs). Laboratory trials were conducted on twelve (12) voluntary, anonymous participants, with the Independent Variable being the colour stimulus, the Dependent Variable being the reaction time of the participants to read the word lists. No interaction took place between the researcher and the participants, apart from the briefing, de-briefing and reading of the word lists. The results revealed significant differences in the mean time to read the words and name the colours across the whole research population, and by participants of different ages. This confirms that interfering stimuli affect cognitive processes. Individual factors such as nationality, mother tongue and familiarity with the test language (English) were not taken into consideration.



Introduction        1

Method        2

Design        2

Participants        2

Materials        2

Procedure        3

Results         4

Description        4

Analysis        5

Discussion        6

Conclusion        7

References        8

Appendices        9

Word count: 1 489


Cognition is the mental process of acquiring knowledge and understanding through thought, experience, and the senses. By studying the mediators between stimuli and the consequential responses, the approach argues that humans process information as computers do, Glassman and Haddad (2004). When conflicting stimuli are sensed, the most strongly developed cognitive process dominates the response.

It is instinctive to read words as they are written, irrespective of the ink colour, because the process of learning to read entrenches the recognition and processing of letters into words. Conversely, the human mind has difficulty in naming colours when words describe another colour.

Stroop (1935) described this interference after studying the effects on attention of conflicting word and colour stimuli. Stroop studied naming colours serially, using solid coloured squares; then introduced words, using incongruent word-colour pairs to act as interference, Engel-Andreasen (2008). This resulted in the research subjects taking longer to name the colours in which the words were printed.  The experiment was a form of operationalisation, as the interference is physically measurable by recording times, Hill (1998).

Jaensch (1929) also studied volunteers’ responses to words printed in incongruent colours.3 Cattell (1885) reported that it was quicker and easier to read words than to name objects and colours aloud, Bower (1992).

This experiment anticipated that the words would influence the ability of the participants to name the colour. The cognitive interference is explained by two possible theories:

  • Speed of Processing Theory: Words tend to be read faster than colours can be named.
  • Selective Attention Theory: The process of naming colours requires more cognitive processing than reading words.



The experiment was conducted in laboratory conditions for maximum control, accurate measurement, and replication purposes. To ensure no prior interaction between the researcher and participants, the latter were selected from lower grades and remained anonymous. Other than briefing, conducting the experiment and debriefing, the researcher and participants did not interact.

Obtaining informed consent from the participants’ parental guardians and requesting permission from the respective teachers to engage their students ensured ethical consistency. The participants were informed of their right to withdraw. As the experiment entailed reading a prescribed list of words (Control Variable), there was no physical, emotional or mental harm. No participants were taken advantage of nor deceived unnecessarily.

The Independent Variable was the colour stimulus, while the Dependent Variable was the time taken to name the colours.

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Opportunity sampling was used to select three participants in each of four age groups (11- and 12-year-olds in Year 7; 16- and 17-year-olds in Year 12). Four participants were male and eight female. To avoid researcher bias, the participants were allocated random numbers and tested individually.


The materials consisted of a consent form for participants (Appendix i (a)); permission letter for teachers (Appendix i (b)); standardised instructions/briefing and de-briefing note (Appendix ii); a raw data collection sheet (Appendix iii); a Stroop word list (Appendix iv); a stopwatch; and numbers (for random participant selection).


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