Verbal responding under a fixed-interval schedule: effects of D-amphetamine

Area of Science:

• Behavioral pharmacology
• Psychopharmacology
• Human operant conditioning

Background:

• Fixed-interval (FI) schedules of reinforcement are used to study response patterns.
• Verbal behavior under schedule control provides a model for human operant responding.
• Stimulants like d-amphetamine are known to affect behavior, but their specific effects on verbal FI responding require further characterization.

Purpose of the Study:

• To investigate the dose-dependent effects of d-amphetamine on the rate and distribution of verbal responding.
• To analyze how d-amphetamine alters response patterning under a fixed-interval schedule.
• To compare the effects of d-amphetamine on human verbal behavior with previously observed effects in non-human species.

Main Methods:

• Human participants produced simultaneous written and spoken narrative monologues.
• Verbal responses (monologue completion) were reinforced under a multiple 5-min fixed-interval (FI) 1-min timeout schedule.
• Doses of d-amphetamine (5-30 mg) or placebo were administered to assess their effects on response rate and patterning.

Main Results:

• d-Amphetamine increased the number of words written and the duration of voice-operated relay (VOR) closure in a dose-related manner.
• The drug reduced the typical post-reinforcement pause observed under the FI schedule.
• d-Amphetamine increased the proportion of verbal responding that occurred early in the interval, altering the characteristic "scallop" pattern.

Conclusions:

• d-Amphetamine alters verbal behavior under fixed-interval schedules by increasing response rate and decreasing pausing.
• The observed effects on response patterning are consistent with those seen in non-human animals under similar schedules.
• These findings contribute to understanding the behavioral pharmacology of stimulants and their effects on operant response control.