Effects of d-amphetamine on observing behavior in the squirrel monkey.
Amphetamine can erase stimulus-controlled behavior in a dose-dependent, rate-dependent way.
01Research in Context
What this study did
Scientists gave squirrel monkeys a simple task. If a light came on, the monkeys could peck a key for food.
The team then injected different doses of d-amphetamine. They watched how the drug changed both looking at the light and key pecking.
What they found
At 0.125 mg/kg and higher, the drug wiped out both behaviors. The monkeys stopped looking and stopped pecking.
A tiny dose helped only the monkeys that already pecked when the light was off. For them, pecking rose a little.
How this fits with other research
Glover et al. (1976) later saw the same drug erase timing patterns in rats. The drug did not just slow the rats; it wrecked their rhythm.
Harris et al. (1978) showed the direction of the effect depends on past training. Rats with a slow history sped up; rats with a fast history slowed down. This explains why the 1969 monkeys with already-low rates simply quit.
McIntyre et al. (2002) tested pigeons on a timing task. They proved the drug changes rate, not the internal clock. Together, the four papers show amphetamine’s main action is rate-dependent: it pulls every behavior toward the middle, often wiping out delicate stimulus control.
Why it matters
If you consult on cases where clients take stimulant medication, remember the drug can abolish subtle, stimulus-controlled skills. Check baseline rates first. A child who barely initiates may stop entirely after a dose increase, while a hyperactive peer might perk up. Always re-assess stimulus control after any medication change.
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02At a glance
03Original abstract
Four squirrel monkeys were trained to press a lever, which produced stimuli indicating availability or non-availability of reinforcement for pushing a key. Food reinforcements were available for the key response at random intervals with an average rate of 1 per min. When food was available, a single lever response produced a red light behind the key. Reinforcement availabilities and red keylights remained until terminated by a reinforced key response. When reinforcement was not available, each lever response produced a 0.5-sec green light on the key. Except after lever responses, the key remained dark. Under this procedure, lever responses functioned as observing behavior in that they produced discriminative stimuli correlated with the availability or non-availability of reinforcement for key responses. The procedure generated a high rate of responding on the lever, short latencies of the key response after onset of red lights and few responses to the key in the absence of red lights. Intra-muscular d-amphetamine, in doses from 0.125 to 1.0 mg/kg, abolished both observing behavior and key responding for periods that increased as a function of dose. However, both observing and key rates were increased at the smallest dose in two subjects whose performances included responding to the key in the absence of red lights. Results are discussed in relation to previous findings regarding effects of amphetamines on operant behavior and on observing and monitoring performance.
Journal of the experimental analysis of behavior, 1969 · doi:10.1901/jeab.1969.12-977