attention-deficit/hyperactivity disorder (adhd): delay-of-reinforcement gradients and other behavioral mechanisms

Abstract

sagvolden, johansen, aase, and russell (sagvolden et al.) examine attention-deficit/hyperactivity disorder (adhd) at levels of analysis ranging from neurotransmitters to behavior. at the behavioral level they attribute aspects of adhd to anomalies of delay-of-reinforcement gradients. with a normal gradient, responses followed after a long delay by a reinforcer may share in the effects of that reinforcer; with a diminished or steepened gradient they may fail to do so. steepened gradients differentially select rapidly emitted responses (hyperactivity), and they limit the effectiveness with which extended stimuli become conditioned reinforcers, so that observing behavior is less well maintained (attention deficit). impulsiveness also follows from steepened gradients, which increase the effectiveness of smaller, more immediate consequences relative to larger, more delayed ones. individuals who vary in the degree to which their delay gradients are steepened will show different balances between hyperactivity and attention deficit. given the range of adhd phenomena addressed, it may be unnecessary to appeal to additional behavioral processes such as extinction deficit. extinction deficit is more likely a derivative of attention deficit, in that failure to attend to stimuli differentially correlated with extinction should slow its progress. the account suggests how relatively small differences in delay gradients early in development might engender behavioral interactions leading to very large differences later on. the steepened gradients presumably originate in properties of neurotransmitter function, but behavioral interventions that use consistently short delays of reinforcement to build higher-order behavioral units as a scaffolding to support complex cognitive and social skills may nonetheless be feasible.