A detailed analysis of the effects of d-amphetamine on behavior under fixed-interval schedules.
Look at response probability across small time slices, not just overall rate, to catch drug or schedule effects you would otherwise miss.
01Research in Context
What this study did
Hymowitz et al. (1974) watched how d-amphetamine changed behavior on a fixed-interval schedule. They broke each interval into small time slices. Then they asked: does the drug change the chance of a response in each slice?
The team did not just count total responses. They tracked response probability moment-by-moment. This let them see where in the interval the drug helped or hurt.
What they found
The drug effect shifted across the interval. Early segments looked different from late segments. Average response rate alone missed these shifts.
Response probability in each slice gave a clearer picture than overall rate.
How this fits with other research
Falk (1966) first showed that longer fixed-interval schedules make rats drink more water between pellets. Hymowitz et al. (1974) used the same schedule length idea, but looked at operant response probability instead of adjunctive drinking. Both papers say interval length controls behavior, just different forms.
O'Leary et al. (1979) later repeated the moment-by-moment pattern in humans. People walked more early in the interval, then less later. This extends N’s segmentation idea from lever presses to whole-body movement and from nonhumans to people.
Bernal et al. (1980) gave ethanol instead of d-amphetamine and also saw schedule-dependent shifts. Their dose curves moved with baseline rate, matching N’s warning that raw averages hide important detail.
Why it matters
When you review a client’s data, slice the session into parts. Check response probability in each part instead of only counting total responses. A drug, a token schedule, or a self-monitoring program can look flat when you average, yet show clear help or harm in specific segments. Graphing those slices lets you adjust timing, dose, or reinforcement so the help lands where it is needed most.
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02At a glance
03Original abstract
Pigeons were exposed to fixed-interval schedules of food reinforcement with durations of 300 sec, 100 sec, or 40 sec. A range of doses of d-amphetamine was administered to each pigeon, and the resulting behavior was analyzed at several levels of detail. Average rates in different portions of the intervals predicted the magnitude of the drug's effect, but a finer analysis showed that average rates did not adequately characterize the behavior in some parts of the intervals. The probability of responding in different parts of an interval without drug was also a good predictor of the magnitude of the effect of d-amphetamine, and at the same time was more descriptive of the interval-to-interval performance. Analyses of the control performance indicated that responding in individual intervals could be described as consisting of two parts: a very low, or zero, rate at the beginning of the interval followed by an abrupt transition to a slightly, but reliably, positively accelerated rate maintained until reinforcement.
Journal of the experimental analysis of behavior, 1974 · doi:10.1901/jeab.1974.21-519