About the stroop test

As adults, many things that we do, we do automatically, almost without thinking. We look in the correct direction before crossing the road; we travel to work without consciously making decisions about the route. Being able to do these things automatically frees up our brain to work on other, more important issues. However, on some occasions, being able to prevent ourselves from doing things automatically, or avoid the usual routine action, is also an important human skill. For example, it is this capacity, known as inhibitory control, that enables us to be polite when we're given an unwanted present, or to avoid taking the usual route to work to avoid a burst water main. Occasionally, this skill of inhibitory control fails us and we act automatically, without thinking. We might lose our inhibitory control after a glass of wine, finding that we inadvertently offend someone by speaking our mind.

As children, almost as soon as we learn to perform actions we also begin to learn how to prevent them. A child's inhibitory control is general poorer than an adult’s. Because of this, we often think that children do things ‘without thinking’ or seem to react automatically. When a young child kicks a football onto a road we worry that they may run out, without thinking, as they automatically chase the ball. As children get older, we worry less. An older child may still want to chase the ball but is able to prevent the chasing action when they reach the kerb. In the preschool years, children have little inhibitory control, they learn new skills quickly and they learn to do things automatically and efficiently. This is a great way for young children to learn but sometimes leads them to say or do things inappropriately.

Most children learn to control their actions as they get older but some continue to have difficulties in controlling automatic actions. In extreme cases, these children continue to act without thinking, blurt out comments inappropriately, seem overactive, and are easily distracted. Amongst other symptoms, this kind of behaviour is characteristic of children with Attention Deficit Disorder or ADD.

Psychologists have developed tests that help us to assess an individual’s inhibitory control. Usually, these tests require someone to suppress an automatic response in order to perform the task correctly. A classic example of such a test is the Stroop test. The Stroop test uses word reading as an automatic process. Most of us find it hard to prevent ourselves from reading words in front of us, for example:

DON’T READ THIS!

When carrying out a classic Stroop test, we ask people to read words written in coloured ink. In order to perform the task correctly, participants are instructed to name the colour of the ink, such as:

TABLE
LEGAL
BURST

In this case, the correct responses are “red”, “blue” and “green”, the colours of the ink. In the classic Stroop test, the words themselves are names of colours but the actual colour is different to the name. The participant is asked to name the colours of the ink, not to read the words themselves, for example:

BLUE
GREEN
RED

Again, the correct responses are “red”, “blue” and “green”. This time, notice how difficult it was to ignore the written word. When performing this task, we find that the automatic word-reading process interferes with our ability to name the ink colour of the word. This interference causes us to make more errors and to be slower in performing the task.

Some people are relatively good at this Stroop task. They are able to inhibit the automatic reading response and ignore the word, performing the task quickly and with very few errors. Others have difficulty with the task and may make errors or do it very slowly. These differences between people may indicate different capabilities in terms of inhibitory control. Just as people differ in their memory abilities, people differ in their inhibitory control. For each individual, inhibitory control may change during the day, for example if we are tired or have drunk alcohol. These changes in inhibitory control will be reflected in our performance on the Stroop task.

Being able to assess an individual’s inhibitory control is important, particularly if they have extreme problems in this area. Neuropsychologists study inhibitory control and how it is affected by brain damage, because problems with inhibitory control are common complaints after a head injury.

Children have more difficulty with the Stroop task than adults. This is not because they are abnormal but because their capacity to inhibit has not reached full maturity. By the time children reach mid-adolescence, their ability is almost fully mature and they perform inhibitory control tasks at a similar level to adults. When attempting to measure inhibitory control in young children, there are some difficulties. Take for example, the Stroop task. Because reading is not well established or fluent in children, we cannot assume that reading is automatic. In children under 6 years of age, we cannot use the Stroop task at all because these children can rarely read the words. In this case, children would perform relatively well on the Stroop task. However, this would not be because they were able to inhibit word reading very well, but because they experience no interference as they were not faced with automatic word reading.

In order to assess inhibitory control in children, we need to look at the kinds of task that children do perform automatically. The animal-stroop task is one task that has been developed specifically for use with children. This task assumes that a child can easily name pictures of animals, such as:

"duck"	"sheep"

Most children over the age of three or so have little difficulty in naming these animals very quickly. In fact, young children will name these pictures without any prompting, i.e. “automatically”.

In the animal-stroop task, we ask children to look at pictures where the head of the animal has been swapped with another animal. In this case, we ask the child to give us the name for the “body” of the animal. Because the face of the animal pictures is so prominent, children find it difficult to ignore. Therefore, just as with the coloured word version of the Stroop task, children have to inhibit the response based on the face in order to correctly name the body of the animal.

Research conducted using this task has found that children experience the same pattern of difficulties with the animal-stroop task that adults have with the coloured word Stroop task.

To find out more about inhibitory control, you can read an extract from the Open University's Child Development course (ED209), executive functions in childhood.