Academic journal article The Psychological Record

A Human-Operant Investigation of Preceding- and Following-Schedule Behavioral Contrast

Academic journal article The Psychological Record

A Human-Operant Investigation of Preceding- and Following-Schedule Behavioral Contrast

Article excerpt

Behavioral contrast occurs when a change in the rate of reinforcement in one context results in a change in behavior in the opposite direction in another context (Rachlin, 1973; Reynolds, 1961). Contrast is typically studied in multiple (mult) schedules: at least two alternating schedules of reinforcement (i.e., components), each associated with its own discriminative stimulus (Ferster & Skinner, 1957). During baseline, all components are associated with the same schedule of reinforcement. During a contrast condition, the schedule of reinforcement in one component (the varied component) is manipulated. Contrast is assessed in unchanged components (target components) by expressing behavior as a proportion of their baseline response rates. Positive contrast occurs when the rate of reinforcement in the varied component is decreased and behavior in the target component increases (proportion of baseline greater than 1.0). Conversely, negative contrast occurs when the rate of reinforcement in the varied component is increased and behavior in the target component decreases (proportion of baseline less than 1.0).

Research suggests that the magnitude of contrast depends on whether the change in reinforcement occurs in the preceding versus in the following component (Williams, 1979, 1988; Williams & Wixted, 1986). For example, Williams (1981) used a three-component (ABC) mult schedule in which Components A and C were target components and reinforcement was delivered according to the same variable-interval (VI) 3-min schedule across conditions. The schedule of reinforcement in Component B varied (VI 1 min or VI 6 min) across conditions. Variations in Component B resulted in larger contrast in Component A than in Component C. With respect to the target components (A and C), the following schedule influenced behavior to a larger degree (B followed A) than the preceding schedule (B preceded C).

Research comparing positive and negative contrast, however, suggests that the relation between following and preceding schedules and contrast holds for positive contrast only. For example, Weatherly, Melville, Swindell, and McMurry (1998) found that negative contrast was larger in the target component preceded by the varied component (the opposite of the relation with positive contrast), and Williams (1992b) found similar magnitudes of negative contrast regardless of whether the target component was preceded or followed by the varied component. Generally, researchers have found that positive contrast is easier to produce than negative, and that the magnitude of positive contrast is larger than negative (McSweeney, Dougan, Higa, & Farmer, 1986; Pliskoff, 1963; Wilton & Gay, 1969).

In addition to molar changes in behavior, contrast has been analyzed on a molecular (i.e., within component) level. For example, Williams (1988) used a three-component mult schedule in which Components A and C were targets and reinforcement was delivered according to the same VI 90-s schedule across conditions. The schedule of reinforcement in Component B varied (VI 30 s or VI270 s) across conditions. To examine within-component effects, Williams divided Components A and C into bins and calculated the extent to which behavior changed across conditions within each bin. Contrast in Component A increased as time progressed into the component (i.e., across bins), while contrast in Component C decreased as time progressed. Several terminological conventions have been used to describe within-component effects, but, for the purpose of this paper, within-component contrast in Component A (largest magnitude of contrast at the end of the component) will be referred to as anticipatory contrast (Williams, 2002). Within-component contrast in Component C (largest magnitude of contrast at the beginning of the component) will be referred to as preceding-local contrast. Researchers have consistently demonstrated preceding-local contrast but have had difficulty reliably demonstrating anticipatory contrast (Weatherly et al. …

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