Reinforcement and response inhibition in children with attention-deficithyperactivity disorder

This thesis reports on two studies which examined possible inhibitory deficits in children with attention-deficit/hyperactivity disorder (ADHD), as well as the children's response to reinforcement contingencies. In the first study, a go/no-go discrimination learning task developed by Newman, Widom, and Nathan (1985) was used to investigate the effects of reward and response costs on the ability of ADHD and normal children to learn to respond to some stimuli and inhibit responding to others. Children were tested on four conditions involving different combinations of rewards and response costs. ADHD children showed poorer inhibitory control compared to control children across the four conditions, implicating a generalized inhibitory deficit. Study 2 assessed the psychophysiological responses of ADHD and control children to reward and the termination of reward during a repetitive motor task. Based on Gray's (1982, 1987a, 1987b) psychobiological model, Fowles (1980, 1988) suggested that heart rate increases during reward are reflective of activity in Gray's hypothesized behavioral activation system, while skin conductance increases when reward is removed are reflective of activity in his behavioral inhibition system. Compared to control children, ADHD children failed to show the expected increase in skin conductance during extinction, implicating a deficit in their behavioral inhibition system. In addition, ADHD children showed faster heart rate habituation to reward which, together with other evidence discussed, suggests that they also have behavioral activation abnormalities. This, the findings from the two studies provide strong evidence that ADHD children have both generalized inhibitory deficits and an abnormal response to rewards which, in some situations, may exacerbate their poor inhibition