Delayed and Current Stimulus Control in Successive Discriminations

Abstract

In a successive discrimination in which successively alternating red and green hues signaled component variable-interval schedules, sensitivity of the ratio of responses in the two components to variation in the component reinforcer ratio decreased systematically during the course of the component. This decrease in stimulus control or discrimination over the course of the component was shown to be the result of delayed control of responding during the component by the stimulus transition between components. When the red-green stimulus transition was altered by interpolating a white stimulus at the end of each 60-s component, discrimination at the beginning of the component (measured by the power-function exponent for sensitivity to reinforcement) was reduced. Conditions with the white stimulus inserted in other quarters of the component indicated that the current discriminative stimulus exerts control over responding throughout the component, whereas during about the first half of the component, response differentials are influenced by the transition between discriminative stimuli.

Action at a Temporal Distance: Component Transition as the Relational Basis for Successive Discrimination

“…The result summarized in Figure 2 confirms the time-related decrement in discriminability over the course of the component reported in previous studies (McLean & White, 1981;White, 1990;White et al, 1984White et al, , 1985. For all three sets of reinforcement-rate conditions, discrimination, as measured by the exponent m of the power function relating response ratios to reinforcer ratios, was highest in the first 10 s of components and decreased systematically with increasing time since component transition.…”

“…The increase in m over the component in the 10-s blackout condition for Bird J2 was consistent with absolute response-rate changes over the component. In the VI 40 VI White (1990) in terms of delayed control by component transition and is inconsistent with the possibility of stimulus control by the transition into the impending component. The value of m for the last 10-s subinterval in the 10s blackout condition for Bird J2 represents a large response differential, however, and given the implausibility that the preceding component transition was influential, raises the question of the source of the discriminative stimulus control.…”

“…In terms of relational theories of discrimination, the opportunity for "stimulus comparison" is said to be an important factor (Lashley & Wade, 1946;Lawrence, 1963;Mackintosh, 1974). White (1990) concluded that the stimulus relation in question is the transition between the component stimuli.…”

“…But in terms of discrimination, local contrast is a decrement in discrimination with increasing time since component transition, rather than an enhancement of the discrimination soon after component transition. White (1990) showed that the high values of m at the beginning of components were the result of strong stimulus control by the transition between the component stimuli, and that the decrease in values of m with increasing time since component transition reflected the diminishing effect of delayed control by the component transition. When the transition was eliminated by replacing red or green discriminative stimuli at the end of the preceding component with the same white stimulus in both components, the discrimination was reduced.…”

“…Further, because the value of m is independent of the reinforcer differential, it could be appropriately described as stimulus discriminability. White (1990) has argued that the temporally related decrement in discrimination reported for successive discriminations by Mc-Lean and White (1981) constitutes evidence for their relational basis. This effect is a reduction in the value of m for the function relating response ratios to reinforcer ratios (Equation 1) during the course of components.…”