Attention-deficit/hyperactivity disorder (ADHD) is currently defined as a cognitive/behavioral developmental disorder where all clinical criteria are behavioral. Inattentiveness, overactivity, and impulsiveness are presently regarded as the main clinical symptoms. The dynamic developmental behavioral theory is based on the hypothesis that altered dopaminergic function plays a pivotal role by failing to modulate nondopaminergic (primarily glutamate and GABA) signal transmission appropriately. A hypofunctioning mesolimbic dopamine branch produces altered reinforcement of behavior and deficient extinction of previously reinforced behavior. This gives rise to delay aversion, development of hyperactivity in novel situations, impulsiveness, deficient sustained attention, increased behavioral variability, and failure to "inhibit" responses ("disinhibition"). A hypofunctioning mesocortical dopamine branch will cause attention response deficiencies (deficient orienting responses, impaired saccadic eye movements, and poorer attention responses toward a target) and poor behavioral planning (poor executive functions). A hypofunctioning nigrostriatal dopamine branch will cause impaired modulation of motor functions and deficient nondeclarative habit learning and memory. These impairments will give rise to apparent developmental delay, clumsiness, neurological "soft signs," and a "failure to inhibit" responses when quick reactions are required. Hypofunctioning dopamine branches represent the main individual predispositions in the present theory. The theory predicts that behavior and symptoms in ADHD result from the interplay between individual predispositions and the surroundings. The exact ADHD symptoms at a particular time in life will vary and be influenced by factors having positive or negative effects on symptom development. Altered or deficient learning and motor functions will produce special needs for optimal parenting and societal styles. Medication will to some degree normalize the underlying dopamine dysfunction and reduce the special needs of these children. The theory describes how individual predispositions interact with these conditions to produce behavioral, emotional, and cognitive effects that can turn into relatively stable behavioral patterns.

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College students' presses on a telegraph key were occasionally reinforced by light onsets in the presence of which button presses (consummatory responses) produced points later exchangeable for money. One student's key presses were reinforced according to a variableratio schedule; key presses of another student in a separate room were reinforced according to a variable-interval schedule yoked to the interreinforcement intervals produced by the first student. Instructions described the operation of the reinforcement button, but did not mention the telegraph key; instead, key pressing was established by shaping. Performances were comparable to those of infrahuman organisms: variable-ratio key-pressing rates were higher than yoked variable-interval rates. With some yoked pairs, schedule effects occurred so rapidly that rate reversals produced by schedule reversals were demonstrable within one session. But sensitivity to these contingencies was not reliably obtained with other pairs for whom an experimenter demonstrated key pressing or for whom the reinforcer included automatic point deliveries instead of points produced by button presses. (1974) found that response-dependent reinforcers maintained higher response rates in pigeons than responseindependent reinforcers, but Streifel (1972) found no difference in the response rates maintained by response-dependent and responseindependent reinforcers with two of three humans. Herrnstein (1970) found that the proportion of a pigeon's total responses maintained by each of two concurrent variableinterval schedules approximately matched the proportion of the total reinforcers provided by each schedule, but Schmitt (1974) failed to obtain such matching with human concurrent responding. In fixed-interval (FI) performances, infrahuman responding is typically characterized by a scallop (i.e., a postreinforcement pause followed by a gradually increasing response rate within individual intervals: Ferster and Skinner, 1957), but the Fl performance of humans is commonly characterized by high rates without postreinforcement pauses (e.g., Weiner, 1969Weiner, , 1970. Yet an organism's sensitivity to schedule contingencies is simply sensitivity to the differential consequences of its own behavior, and it is puzzling that human responding often appears less sensitive than that of other species.