What is ‘executive function’?
There are two main types of human action. One includes habitual behaviours, like driving along a well-known route, that involve automatic responses and need little or no effortful, conscious processing. The second type includes flexible, adaptive responses to new or difficult situations, such as driving in an unfamiliar city. Executive function is an umbrella term used to describe the processes underlying this second type of action. More specifically, executive function is needed in situations that involve:

• the learning of new skills
• planning and decision making
• error correction or troubleshooting
• initiating novel sequences of actions
• danger or technical difficulty
• conscious moment-to-moment control of behaviour
• the need to overcome strong habitual responses

The development of executive function in children
For much of the twentieth century, research on executive function centred almost exclusively on adults. This was mainly because the prefrontal cortex was thought to become functionally mature only late in development, around adolescence (Luria, 1973).

However, it has become increasingly clear that the onset of the development of executive function occurs much earlier than was previously thought. This has become apparent following the appearance of more appropriate tools for studying it at earlier ages. In this section we will look at the course of one aspect of early executive function development; inhibitory control.

Inhibitory control
We have seen in other chapters in this book that one aspect of child development concerns the progressive organization of children’s behaviour and experience. One factor that underpins this is a developing ability to inhibit responses to stimuli. Why is this so important?

Activity: The richness of the sensory world
This activity encourages you to reflect on the complexity of your everyday environment.

Consider your sensory world. Look around the environment you are in. Try to observe everything you can see. Then sit back, shut your eyes and listen to everything that you can hear.After that, focus on what is touching you. Attend to each part of your body in turn. What can you feel? It takes a few minutes to get the most out of this activity, so do not hurry it.

Comment
The richness and complexity of the assaults on your senses are considerable. However, it ishard to experience this complexity to its full extent because the mature human mind is soexpert at filtering out irrelevance, and building stimuli into simpler, more meaningful (andorganized) patterns. If this ‘filtering’ did not take place, and you gave equal weight to allincoming sensory information, it would be impossible to behave in anything but a chaotic manner.

Your current plan of action probably revolves around reading these words. In order to do this successfully you have to be able to ignore most of the sensory world around you. You have to be able to prioritize the meaningful stimuli – the type that makes up the words – and inhibit responses to irrelevant stimuli, in order to enact your plan of reading the current paragraph,and to achieve the goal of finishing it.

What if you were unable to do this? What if you could not give the words on the page any greater priority in cognition than the grain of the wood on the table on which your keyboard is resting? What if you were unable to inhibit responses to the sound of the computer fan as it whirrs in the background, or the feel of your feet on the carpet?

If you were unable to inhibit responses to stimuli that do not relate to the task that you have planned to do, then it would probably be impossible to complete it and achieve your goal. You would be drawn from one stimulus to another, in a haphazard fashion, and it would be impossible to undertake any coherently organized action.

This is a rather extreme way of conveying the point, but young children and people with executive function related disorders of inhibitory control do have difficulty in prioritizing their response to task-related stimuli, and do have difficulty in inhibiting responses to what are referred to as ‘prepotent’ stimuli.

A prepotent stimulus is a stimulus that draws a person’s attention towards it, and which seems to cause the person to behave in a particular way (the prepotent response). Prepotency is a very important feature of effective everyday functioning. It is to be hoped, for example, that a red traffic light would draw adriver’s attention towards it, and cause the driver to behave in a certain way. Thesight, smell and feel of the mother’s breast are the most likely prepotent stimuli for the young breast-feeding infant.

In the course of typical development it is possible to observe infants and young children being distracted by inappropriate prepotent stimuli. By ‘inappropriate’ we mean stimuli that are nothing to do with the child’s current plan of action. For example, one might observe an 8-month-old infant catch sight of a toy on the other side of the room and begin crawling towards it. It is clear to an observer that they are enacting a plan to get the toy, but halfway across the room the infant notices a scrap of paper on the floor.

This seems to ‘capture’ their behaviour and their attention. They pick it up, sit down and inspect it. The original plan is now lost and they have been catapulted onto another stream of behaviour, which might involve another plan, which might itself get interrupted by another prepotent stimulus, and so on and so forth. This executive function analysis of a familiar scene offers one explanation of why infant behaviour sometimes appears somewhat haphazard and disorganized to an adult onlooker – according to this view it is because executive functions are as yet undeveloped.

One aspect of child development that psychologists have become interested in, then, is the way in which children develop an ability to inhibit responses to stimuli that are nothing to do with their current plan of action. Put another way, this amounts to an ability to prioritize responses to task-relevant (as opposed to task-irrelevant) stimuli. When children begin to be able to do this, their behaviour becomes less haphazard, and progressively more strategic and organized.

Measuring the development of inhibitory control
Psychologists use a number of methods to measure the development of inhibitory control. One widely used technique is known as the Stroop task.

Activity: The Stroop task
This activity allows you to do the Stroop task and gives you a way of experiencing prepotency directly.

Now, out loud, and working as accurately and as a quickly as you can, call out the colour in which each word is written. What happens?

Comment
You should find that after a few words you start to get confused, wanting to call out the word that you are reading, rather than the colour of the ink in which it is written. The meaning associated with the word is acting as a powerful prepotent stimulus. You have to inhibit everything you have learned about words and their meaning in order to call out the colour of the ink. You could take two measures of performance from this, each of which would give some information about inhibitory control: speed of completion, and number of errors made.

Why do you think that this task is not suitable for children of, say, 3 years of age?

The Stroop task tends to be used with older children and adults because of the demands it makes on literacy skills, which in themselves are not a component of executive function. Indeed young children’s limitations with respect to language processing pose a problem in finding age-appropriate executive function tasks. Children’s levels of verbal comprehension may influence their overallperformance on tasks that have complex instructions or written stimuli, and this decreases the validity of such tasks as measures of executive function.Consequently, tests for young children need to be kept as simple as possible. The Handgame and the Knock/Tap game are good examples of sometasks that have been designed to minimize the importance of written language skills. (You may also like to try a similar test, What's the animal?)

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Content last updated: 06/01/2005

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