Conjoint Control of Performance in Conditional Discriminations by Successive and Simultaneous Stimuli

Abstract

In a conditional discrimination, reinforcement of pigeons' responses to pairs of simultaneously presented wavelength stimuli depended on the orientation of white lines superimposed on the wavelengths. Over different conditions in Experiment 1, three wavelength differences were combined with two differences between successively presented line orientations. Measures of stimulus discriminability increased with increases in the difference between both orientation and wavelength stimuli. Conditional-discrimination performance was thus conjointly determined by stimulus disparity in the successive and simultaneous discriminations. In Experiment 2, ratios of rates of reinforcement contingent upon the two categories of correct responses were varied over several conditions for difficult and easy discriminations. Ratios of responses to wavelength pairs were sensitive to variations in the reinforcement ratio to a greater extent for the more difficult orientation discrimination than for the easier orientation discrimination. Performance in the conditional discrimination was therefore determined by the interacting effects of stimulus disparity and the relative rates of reinforcement contingent upon the two correct choices. It was concluded that the effect of temporally distant reinforcement on behavior in a prevailing schedule component is attenuated to an extent that depends on similarity of stimuli that delineate the successive components.

Remembering as discrimination in delayed matching to sample: Discriminability and bias

“…Thus, the difficulty of the DMTS task is related to the length of the retention interval. As in the simple matching task (White, 1986), the result of increasing task difficulty by increasing the retention interval leads to a greater influence on the animal's responses by the probability of reinforcement associated with each choice, as was found by Hartl and Fantino (1996) and Jones and White (1992).…”

“…Even if the probability of reinforcement for one alternative is low, the obtained reinforcement will be maximized by the animal's making correct choices, and not by its favoring the alternative associated with the higher rate of reinforcement. However, as the discrimination becomes more difficult, the animal's choice is influenced to a greater extent by the reinforcement ratio, an intuitively plausible result (White, 1986;White, Pipe, & McLean, 1985;Wixted, 1989). In White's (1986) experiment, one response was correct following the presentation of a line of 0º, and another response was correct following the presentation of a line of 90º.…”

“…However, as the discrimination becomes more difficult, the animal's choice is influenced to a greater extent by the reinforcement ratio, an intuitively plausible result (White, 1986;White, Pipe, & McLean, 1985;Wixted, 1989). In White's (1986) experiment, one response was correct following the presentation of a line of 0º, and another response was correct following the presentation of a line of 90º. The discrimination was made more difficult in a separate condition by changing the tilt of the lines to 45º and 60º.…”

Psychophysics of Remembering

“…The separation of discriminability from bias in psychophysics has a parallel in the study of conditional discrimination learning, where the effects of the discriminative stimuli may be separated from the effects of the differential reinforcer probabilities that maintain the discrimination (Nevin, 1981;White, 1986;Williams, 1988). In the context of choice procedures, differential reinforcement biases the choice towards one alternative versus another.…”

“…In conditional discriminations, however, the effects of the reinforcer differential are modulated by stimulus disparity. When choice relies on both stimulus and reinforcer differences, large stimulus differences attenuate the effect of the reinforcer differential and small stimulus differences amplify the reinforcer effect (White, 1986). Signal-detection procedures, which are also classed as conditional discriminations (McCarthy & White, 1987), are associated with a similar problem.…”