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.