People often make erroneous predictions about the trajectories of moving objects. McCloskey (1983a, 1983b) and others have suggested that many of these errors stem from well-developed, but naive, theories of motion. The studies presented here examine the role of naive impetus theory in people's judgments of motion. Subjects with and without formal physics experience were asked to draw or select from alternatives the trajectories of moving objects that were presented in various manners. Results from two experiments indicate that both trajectory judgments and explanations were affected by specific response and display features of the problem. In addition, these data provide little evidence that naive impetus theory plays a significant role in subjects' performance; instead, they suggest that motion judgments and explanations are constructed on the fly from contextual cues and knowledge that is not necessarily naive.

The spontaneous motor activity (SMA) of rats was recorded after injections of saline, d-amphetamine sulfate (0.8 mg/kg), and ethanol (400, 800, 1200, and 1600 mg/kg). Each drug treatment was given separately, and the amphetamine treatment was also combined with each ethanol dose. Ethanol, when injected without amphetamine, produced a dose-related decrement in SMA. Amphetamine, injected without ethanol, produced an increase in SMA. The combination of ethanol at 400 mg/kg with amphetamine potentiated the amphetamine-stimulant effect, but higher doses of ethanol counteracted amphetamine-produced increment in SMA. In a second experiment, similar combinations of ethanol and amphetamine were administered to rats lever-pressing for food pellets under a fixed-interval reinforcement schedule. The effect of amphetamine alone depended on baseline rate and varied among individual rats. Ethanol had a depressant effect on response rates, but combinations of the two drug treatments produced rates that, in most rats, were higher than after any single drug or saline treatment.

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