The effects of chlordiazepoxide and d-amphetamine during a three-component multiple schedule.

Multiple schedules have been used successfully to study drug effects on behavior (Barrett, 2002). Initial studies in behavioral pharmacology showed that a drug’s effect on behavior can be influenced by the schedule of reinforcement that maintains that behavior. For example, when pentobarbital was administered to pigeons trained on either a fixed-interval (FI) 15-min or fixed-ratio (FR) 50 schedule of reinforcement, FI-maintained behavior was changed much more than FR-maintained responding (Dews, 1955). Similar changes in behavior have been observed under multiple schedules of reinforcement (Leander & McMillan, 1974; McMillan, 1969); that is, when the reinforcement schedule alternates between two or more components and a unique schedule-correlated stimulus is presented during each component. Thus, to characterize a drug’s effect, one must take into account the schedule of reinforcement supporting that behavior. In behavior analysis, multiple schedules have been used for research in areas such as stimulus control and contrast. Specifically, Reynolds’ (1961a, b, c, d) initial experiments with multiple schedules stimulated an extensive area of research on how factors outside a particular schedule of reinforcement influence responding during that schedule of reinforcement. At least two main contextual effects have been noted. Contrast is said to occur when changes in the reinforcement rate during one component of a multiple schedule changes responding during an unchanged component in the opposite direction. Conversely, induction is said to occur when changes in the reinforcement rate during one component of a multiple schedule changes the organism’s responding during the unchanged component in the same direction (Reynolds, 1963). More complex interactions have been observed with a three-component multiple schedule of reinforcement, in which reinforcement rates during the first and last components are equal, while reinforcement rates during the middle component are varied (Williams, 1979; Williams, 1981; Williams & Wixted, 1986). Typically, an asymmetry in response rates develops whereby responding during the two identical schedules of reinforcement diverges. This effect has been termed both anticipatory contrast and the following-schedule effect because the response rates most affected by the change in reinforcement rates during the middle component are those that temporally precede that change. Thus, the rate of responding on a given schedule of reinforcement can be modified by the context in which it is occurring; in particular, by the relative rate of reinforcement in the next schedule component. The present research was conducted to evaluate the effects of chlordiazepoxide and d-amphetamine on one type of reinforcement context effect: anticipatory contrast. Multiple schedules allow a way to separate the effects of reinforcement context from history effects and have been used extensively in behavioral pharmacology (Barrett, 2002). The three-component AXB procedure was chosen over a two-component procedure so the effects of context (i.e., the schedule arranged in the X component) could be examined by comparing responding in the A and B components, where reinforcement schedule is held constant. We chose to test chlordiazepoxide because it has consistently been shown to attenuate contrast-like effects in procedures like successive negative contrast (Flaherty, Grigson & Rowan, 1986; Flaherty & Rowan, 1988). Because previous studies have shown that d-amphetamine does not influence contrast with a two-component multiple schedule of reinforcement (Hearst & Vane, 1967; Spealman, Katz & Witkin, 1978), we tested it as a negative control. We examined the effects of these two drugs on multiple schedule performance when reinforcement was either eliminated or increased during the middle component.