Effects of dl-amphetamine under concurrent VI DRL reinforcement.
Stimulant drugs compress DRL pauses through pure motor speed-up, not by erasing the animal’s sense of time.
01Research in Context
What this study did
Segal (1962) gave rats two levers at once. One lever paid off on a DRL schedule. The other paid on a VI schedule.
The team then injected dl-amphetamine and watched how the animals’ pause times changed.
What they found
The drug shortened pauses on the DRL lever. Response bursts still peaked just after the minimum wait time.
The pattern shows the rats still “knew” the rule. The drug simply made them move faster.
How this fits with other research
MOLLIVER (1963) found you can sharpen DRL timing by adding a second, mediating lever that earns conditioned reinforcement. F’s drug did the opposite: it sped the rats up and blurred the pause.
Berler et al. (1982) showed that a brief stimulus before free food can also shorten DRL pauses. Their effect is called external disinhibition. F’s drug effect looks similar but comes from inside the body, not from an outside cue.
Together the three papers map two ways to collapse DRL pauses: add an external cue or add a motor stimulant.
Why it matters
If a client on stimulant medication starts pressing too fast on a DRL program, the drug—not poor instruction—may be the culprit. You can keep the schedule but lengthen the minimum pause, add a mediating response, or insert brief stimulus breaks to protect the timing.
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Join Free →If response bursts shorten after a med change, raise the DRL requirement by 20% and add a mediating step like a hand-down gesture before the next response.
02At a glance
03Original abstract
Three adult, food-deprived rats were given IP injections of dl-amphetamine sulfate under DRL and concurrent VI DRL reinforcement schedules. The drug results were as follows.(1) The IRT distributions of DRL responses shifted to the left, but some temporal discrimination remained. (2) The IRT distributions of VI responses shifted slightly to the left. (3) The distinguishing characteristics of VI and DRL IRT distributions were preserved. (4) The frequency distribution of number of VI responses between two consecutive DRL responses was relatively unaffected. (5) Over-all response rates on the two components of the concurrent schedules increased more or less proportionately. These findings imply that the primary behavioral effect of dl-amphetamine was a motor excitatory one. The drug's disruption of timing behavior was not due to a derangement of internal timing mechanisms, nor to interference with the topography or pattern of behavior. Rather, it might be a secondary result of the accelerated emission of overt behavior patterns mediating the temporal spacing of DRL bar presses.
Journal of the experimental analysis of behavior, 1962 · doi:10.1901/jeab.1962.5-105