At low and moderate doses, these druge poduce motor stimulation, reduc fatigue, increase resistance to sleep, increase vigilance and alertness, heightened mood. ; range of doses in which enhancement occurs, but as dose increases, performance returns to nondrug levels or worse. Generally, signs of increased sympathetic nervous system (increased heart rate, blood pressure) None of the terms mentioned adequately describes the effects of these drugs if the drugs are used in large amounts acutely or moderate amounts chronically. Produce rate-dependent effects on responses; effect of the drug depends on baseline rate of responses generated by the specific category (schedule) response rate (fixed interval) schedules. -low doses=stimulants increase locomotor activity and exploration bobbing, nose poking etc. Major stim-dose increases, increase response frequency increase with decreasing response category. Kill da in nac-supressed locomotor stimulant effects of low doses of amph. Enhance lever pressing when responding on schedules that generate low. Decrease lever-ressing when animals are responding on fixed ratio.