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The Stroop Effect

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The aim of the experiment was test whether automatic processing could affect a colour related task. Previous research has found that the response time of reading the colour of the ink of colour associated words was greater than reading the colour of the ink of neutral words. The experiment retested the Stroop effect to measure the incursion of automatic processing. The results showed that the time to read the ink colour of colour associated words was greater than that of the neutral words and proposed that involuntary interference of automatic process could affect people’s attention during controlled tasks.

Attention is one of the most important cognitive processes that psychologists have researched. It is the mental motion that allows our perceptive processes to review selected areas of our surroundings. One specific type of attention is selective attention, which is when people are instructed to respond selectively to certain kinds of information while ignoring other information. Divided attention refers to the ability to divide ones attention between two or more tasks. If one of these tasks becomes an automatic process it becomes easier to ones attention between these two tasks.

However, sometimes rather than being helpful, interference can occur between the controlled process and the automatic process. Psychologists have frequently found that the powerfully autonomic nature of reading words, as it is such a well-learned automatic activity can interfere with other tasks.

Kanheman (as cited in Edgar, 2007) devised a model of divided attention, which was based around the idea of mental effort. He proposed that some tasks might be relatively autonomic and make fewer demands in terms of mental effort, such as a reading task. Several activities can be carried out at the same time, provided that their total effort does not exceed the available capacity.

Shiffrin and Schneider (as cited in Edgar, 2007) conducted a series of investigations into automatic processes and compared it to controlled processes. They found that the time taken for them to carry out this task significantly increased. This is because the already learned, automatic process was very difficult to change, which shows how automatic processes are fixed and rigid and after practise can become automatic.

Stroop (as cited in Edgar, 2007) carried out an investigation into autonomic processing, by inventing the Stroop effect. In this, he instructed participants to read a list of colour words written in black ink which was quite simple task for the participants to carry out. Following this, participants were asked to read a list of colour words written in conflicting coloured inks, (e.g., the word “red” written in blue colour ink) and to read out the colour ink the words were written in. Although this task seemed very simple at first and is only matter of simple colour recognition, Stroop found that it took the participants noticeably longer to finish this task than the earlier one.

According to the speed of process theory the Stroop effect was viewed as an interference which took place because the words were read faster than colour naming. This theory states that words are easily read than the colours and for this reason the effect occurs. The selective attention theory on other hand states that the Stroop effect occurs because colour naming requires more attention than when a person is reading the word, therefore because of the ease to read words the effect occurs.

The purpose of this research is to carry out an investigation on the Stroop effect by conducting an experiment to measure how long it takes for participants to read out the colours of words on two lists, colour associated words and neutral words to produce evidence to support or challenge the directional hypothesis which states that people find it harder to name what colour ink a word is written in if the word is the name of a colour than if the word is neutral. The null hypothesis is that there will be no difference in the length of time taken for participants to name a set of neutral words and the length of time taken for participants to name a set of colour associated words.

This was a one-tailed, related study. The experiment employed a within participants design. The independent variable was represented by two conditions; two word lists printed in various coloured inks. One list consisted of colour names and the other of neutral words. In both conditions, the dependent variable was the time taken to name the ink colours. This was measured by the examiner using the stopwatch and was accurate to the nearest second. In order to control any differences the experiment took place in a quiet, well lit room and those who had reading glasses were asked to put them on. The visual stimuli were presented in a bold Arial font 36. The instructions given in both conditions were identical except that in one condition they were asked to identify colour words and in the other condition to identify neutral words.

The participants consisted of 20 males and females between the ages of 18 and 70. Sixteen were from amongst the Open University whose data was collected by the university and four were volunteers from a local adult learning centre. All the participants were educated to higher education and spoke fluent English. There were 13 women and 7 men.

Two lists of 30 words placed on two columns were prepared on separate A4 sheets of paper. One list contained colour related words; sky, plum, lemon, grass, blood and carrot. The other was a list of six neutral words; sky, plan, ledge, grade, career, blame. The words were written in six colours; green, yellow, blue, purple, orange and red. Each word appeared five times in its list, the order being randomised and each word was printed in one of the six colours. The colours were randomly distributed between the words, but the same ink colour sequence was followed for both lists. All words were printed on white matt paper. (Appendix1) The auditory stimuli in both conditions consisted of the participants reading out the colours that the words in the visual stimuli were printed and a stopwatch was used to the nearest second to time how long it would take each participant to complete the task. Standard instructions were used to explain what was required of them (Appendix 2) and the all signed consent forms before the task (Appendix 5) The time taken to complete the task was recorded on paper for each participant.


The participants were approached individually and asked if they would like to take part in a psychology experiment that would not take them more than 10 minutes of their time. All the participants who agreed to take part were over 18 and signed a consent form before the experiment (see Appendix 5 for copy of consent form). The experiment was conducted on a one to one basis and before being briefed about the experiment, the participant’s gender and age was recorded and if they understood English. Each participant was informed that they could withdraw from the experiment at any time if they so wished. The instructions for both conditions which were read out to the participants informed them that they would be presented with a sheet of paper with a list of words and that they would be required to state the colour that the word were written in (see Appendix 2 for a copy of the instructions.)

Once the participant stated that they understood what was required of them the list of words from the visual task of condition 1(colour related words) was placed face down in front of them. (see Appendix 1 for visual stimuli) The visual task was then turned over and the experimenter started the stopwatch while the participant started reading out the words. When the participant finished reading out the words, the experimenter recorded the time it had taken to the nearest second. The same was repeated for the condition 2 (neutral words). Ten of the participants began the task with condition 1 then condition 2 and the other ten began with condition 2 then condition 1. The participant was debriefed about the purpose of the experiment and asked if they had any questions.

After the 20 participants completed the task the the data was compiled into a single worksheet to carry out statistical inferences, the data collected is summarised in the table below, and detailed data from the study are available in Appendix 4:

Table 1: Descriptive Statistics
MeanStd. DeviationN
condition 128.758.11720
condition 224.006.05220

From the above Table 1, the average time for the first task is 28.75 the mean for the second task is 24.00 which reflects that it took longer to read the colour associated words than the neutral words. A paired samples t-test was conducted to analyse the data which revealed that the difference between the two conditions was statistically significant (t (19)=4.37;p=00;d=0,67). It was possible to accept the hypothesis that people find it harder to name what colour ink a word was written in if the word was colour associated than if the word was neutral. The null hypothesis was rejected on the basis of this result.


The results as shown in table 1 above reflected a significant increase in the time taken to read the colour words over the neutral words. This corresponds with previously reported data and supports the experimental hypothesis of this study that the Stroop task provides evidence for the automaticity of reading. Although a good reader may be given strict instructions only to attend to the ink colour they cannot suppress accessing the word meaning. Participants are usually slower and less accurate in identifying colour words compared to neutral words.

It has been suggested that the approach of focusing attention on the initial letter of each word reduces the influence of the automatic reading of words and so reducing the overall Stroop effect. This shows that automatic processes are not free processes that require no cognitive resources and may compete with other processes for resources.

Shiffrin & Schneider suggested that the Stroop effect is consistent with a distinction between controlled and automatic processes. A lot of practice on a difficult task that always requires the same response for a given stimulus gradually turns the process from controlled search to automatic search. Attention is slowly inhibited from task control with increasing practice, until the process requires only a minimal amount and is said to be automatic. In automatic search responses are rapid, so that they are difficult to prevent, and also aren’t remembered very well.

The results here indicate that an unconscious process is taking place. Intrusion such as this is coherent with the automatic processes of Kahneman’s model, and with the definitions of automaticity cited by Shiffrin and Schneider. The act of reading is so

well learned that, despite attempting to attend to the colour of the ink, the unconscious process of interpreting the meanings of the words is still going on. If the word names a colour, the meaning of the word conflicts with the participant’s attention to the colour of ink. Gopher (as cited in Edgar, 2007) suggests that the control of attention is a skill that can be learned and modified. The ability of people to use a strategy of focusing attention on the initial letter to overcome the Stroop effect suggests that this is the case.

The cause for an upsurge in reading time is that some participants read both lists at the same time and some of the participants seemed consciously to slow down when reading colour words, possibly to provide more attention. This is because the powerful unconscious nature of reading words meant that participants automatically wanted to read the words rather than the colour ink they were written in. So, even though the participants didn’t often read the colour word out loud, there was a time delay whilst the participants thought of the correct response. In conclusion, the results of the experiment reported here showed that automatic processes interfered with a task of naming colour words.

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