The Handgame is a task that has the same basic structure as the Stroop task from Activity 4. The child must inhibit a prepotent response in order to execute a rule guided action. Specifically, the child is first asked to imitate two hand actions (making afist and pointing a finger). Then, in the conflict condition, children must make the opposite responses (making a fist when the experimenter points their finger and vice-versa). This involves:
- inhibiting the prepotent response to imitate; and
- performing an action guided by the rule ‘do the opposite of what the experimenter is doing’.
The measure of executive function that this task provides is the number of errors in the conflict condition. The task is based on work by Luria and has been used with preschool children. Other variants of this task include Luria’s Knock/Tap game (in which the child must knock when the experimenter taps the table and vice-versa), the Opposite Worlds task (in which school-aged children are asked to say ‘one’ when they see a ‘2’ and to say ‘two’ when they see a ‘1’), and the Day/Night Stroop task (Gerstadtet al., 1994) in which children are instructed to say the word ‘day’ whenshown a line drawing of the moon and stars, and ‘night’ when
shown a line drawing of the sun.
You should be able to see how these tasks relate conceptually to the Stroop task, and how they are better suited to minds that are not yet at the stage of having overlearned (automated) the ability to read words.
Measuring the development of inhibitory control in infancy is particularly challenging. One method that is used is the structured observation of infant performance on certain tasks. Inferences are then made from these observations about inhibitory control. An example of this is the work of Diamond (2002). They observed infants of 8–11 months performing problem-solving tasks such as retrieving an object from an open box. They concluded that 9–10 month-old infants show evidence of inhibitory control, and that even in this narrow age band there was already evidence of older infants maintaining their attention on-task longer than the younger infants.
Most work on inhibitory control in childhood has focused on children who are 3 years of age and over. A range of tasks has been developed that is suitable for use with children of different ages. One of these is the Go/NoGo task (Drewe,1975). In one version of the task different letters are displayed, one after the other, on a computer screen. The child is instructed to press the space bar as quickly as they can whenever a letter is flashed onto the screen (Go), except when that letter is an ‘X’ (NoGo). Errors of commission, when a child presses the space bar mistakenly in response to the letter ‘X’, indicate a failure to inhibit. A variant of this task uses pictures of planes with a cartoon bomb as the ‘NoGo’ stimulus (Rubia et al., 2001).Note that in the ‘Simon says’ game, ‘do this’ (without the preceding ‘Simon says’) is equivalent to a NoGo stimulus.
Using tests such as these researchers have found that there are significant improvements in task performance between the ages of 3 and 6 years. In a study by Mahone et al. (2001), 87 typically developing children completed a computerized Go/NoGo task. Even though the 3-year-old children managed the task with few omission or commission errors, the researchers noted a developmental trend across their sample: increasing age was associated with steady and significant improvements in performance.More complex inhibitory control functions are tapped by non-verbal Stroop tasks (for example, Luria’s Day/Night, Handgame, Knock/Tap). These require children not only to inhibit a response (as in the Go/NoGo task), but also to execute a rule-guided action. The majority of 3 year olds fail the Day/Night task (Gerstadt et al., 1994), the Handgame (Hughes, 1996; Hughes, 1998a and b) and the Knock/Tap game (Perner and Lang, 2002). However, the majority of 4 year olds pass these tasks. Thus significant improvements in both simple and complex inhibitory control are evident in the pre-school years.
Developmental improvements in inhibitory control also continue throughout
childhood, as demonstrated by findings from studies with school-aged children using the Go/NoGo tasks (for example, Manly et al., 2001). Interestingly, findings from a brain imaging study by Casey et al. (1997) that used functional magnetic resonance imaging suggest that children and adultsshow similar patterns of brain activation during the Go/NoGo task, and that this activation is in the prefrontal cortex (see Research summary below).
Research Summary
Inhibitory control and brain activation
Casey et al. (1997) used an fMRI scanner to examine patterns of brain activation during a Go/NoGo task. Nine children and nine adults took part. The children were between the ages of 7 and 12 years, and the adults were between the ages of 21 and 24 years.
The participants undertook a Go/NoGo task that involved responding to any letter that was presented to them on a screen inside the scanner, except for the letter X. Functional MRI scanners are like a large, narrow tube into which the participant is slid on their back, so a hand-held device was specially constructed to record the participants’ responses.
The researchers found that during the task adults and children showed the same location of brain activation within the prefrontal cortex. However, they also observed that the amount of activation was significantly greater for the children. The interpretation of this finding is complex, but it is likely to relate to the fact that the task places more demands on executive functions for children than for adults.
For adults the executive demands of the task are probably lower. This interpretation is supported by the fact that the adults performed better than the children on the task. Soas suggested in earlier sections of this chapter, and in Chapter 3, Section 5, increasing skill in a task is associated with decreasing involvement of the prefrontal cortex and executive function. The association between the prefrontal cortex and executive function is shown in the correlation reported by the researchers between levels of prefrontal activity and success on the task. Specifically it was found that increasing levels of prefrontal activity were associated with greater accuracy of performance (fewer errors of commission).
Inhibitory control in child development
The picture of development that has been built up in this section is one that shows the child gradually mastering the inhibitory control component of executive function. Development in this respect is already detectable in infancy and continues well into the school years.
Although it is not sensible to ask at what age this development is ‘complete’ (development does not just stop when a child becomes an adult), we can ask at what age it becomes impossible to distinguish between child and adult performance on standardized measures. In this respect Chelune and Baer (1986)have reported a steady improvement in performance on the Wisconsin Card Sorting Test from 6 years of age, with participants achieving adult levels of performance by around 10 years of age. This finding has been replicated in subsequent studies (for example, Levin et al., 1991; Welsh et al.,1991).
Executive function plays a crucial role in the early stages of mastering new skills. When a child is learning to read, the executive demands of the activity are high. A great deal of conscious effort is required on the part of the novice reader simply to decode the written symbols into words. So much conscious effort is required that, as was noted earlier, there may be insufficient cognitive resources to interpret the meaning of the text that is being read. Gradually, as reading skill increases, the executive demands of decoding diminish. The child becomes able to read the words ‘automatically’ and can allocate more resources to the business of constructing meanings. If you consider the development of any skill you will see that the involvement of executive function is greatest when the actions involved are still novel. As mastery of the skill develops,so the role of executive function diminishes, and automated action takes over.There is something of a paradox here: executive function is least well developedin the very people who need it most in order to develop new skills – young children.
As executive function develops, so children’s abilities to learn new skills improve, and they are increasingly able to behave in a planned, strategic and organized manner. They are able to stay ‘on-task’ longer. They are able, when necessary, to override habitual responses to prepotent stimuli. They become more skilled and flexible in ‘orchestrating’ elements of their thinking and behaviour, and they are able to engage in increasingly sophisticated planning and decision-making. Inhibitory control is only one component of this developmental trajectory, but it is of fundamental importance. One way to assess this importance is to look at the implications for child development of a failure to develop typical levels of inhibitory control.
Summary
- The ability to inhibit responses to prepotent stimuli is a prerequisite for planned, intelligent action.
- Some components of executive function are already developing in preschool children, and play a much greater role in early child development than previously thought.
- Adult levels of performance on a standard measure of executive function are achieved by around 10 years of age.
- Executive function plays a crucial role in the initial mastery of new skills, before the skills become automated.
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