大河内 浩人

The present study examined whether bidirectional response-response relations could be established without direct reinforcement. In AB training for 12 undergraduates, higher rates of touches to a white circle on the monitor screen (A1) produced two stimuli (B1 and B2) on half of the trials, whereas lower rates (A2) produced the same effect on the other half. Choosing one of the two stimuli was reinforced according to the preceding responding (A1B1 and A2B2). In BC training, touching a stimulus (B1 or B2) produced three white circles lined up horizontally on the screen, after which one of two different response sequences to the circles (left-center-right, C1 or C2, and right-center-left, C2 or C1) were reinforced, depending on the stimulus presented (B1C1 and B2C2). After AB and BC relations were established, 11 of 12 participants showed the emergence of untrained relations (BA, CB, AC, and CA) throughout five test sessions, and the remaining participant showed it in the first four test sessions. These response-response relations were replicated with five other undergraduates and different trained relations.

Two experiments were conducted to assess stimulus control and generalization of remote behavioral history effects with humans. Undergraduates first responded frequently under a fixed-ratio (FR) schedule in the presence of one line length (16 mm or 31 mm) and infrequently on a tandem FR 1 differential-reinforcement-of-low-rate (DRL) schedule when a second line length (31 mm or 16 mm) was present. Next, an FR 1 schedule in effect in the presence of either stimulus produced comparable response rates between the stimuli. Finally, a tandem FR 1 fixed-interval (FI) schedule was in effect under those same stimuli (Experiment 1) or under 12 line lengths ranging from 7 to 40 mm (Experiment 2). In both experiments, responses under the tandem FR 1 FI schedule were frequent in the presence of stimuli previously correlated with the FR schedule and infrequent in the presence of stimuli previously correlated with the tandem FR 1 DRL schedule. Short-lived but systematic generalization gradients were obtained in Experiment 2. These results show that previously established rates of behavior that disappear when the establishing contingencies are changed can subsequently not only reappear when the contingencies change, but are controlled by and generalize across antecedent stimuli.

A matching procedure was used to examine whether humans discriminate fixed-interval (FI) schedules. Fixed-ratio (FR), FI, or differentialreinforcement- of-low-rate (DRL) schedules were in effect during a sample schedule link. Responses meeting the schedule requirement produced a choice link in which each of three circles was presented with a unique color. The choice was reinforced depending on the schedule of the sample link. In Experiment 1, a correct response equal to or higher than 94.4% was obtained for each sample schedule in each of the four undergraduates. Post hoc analyses suggested that time spent with the sample schedule link may have functioned as a discriminative stimulus of the choices. In Experiment 2, after replicating the schedule discrimination with additional four participants, the FI value was changed to equate to the mean time spent in the FR or DRL schedule link. With this modified FI value, the accuracy was deteriorated but eventually recovered, whereas the lengths of time spent in the sample schedule links diverged across the schedules. Previous studies have shown that humans were insensitive to reinforcement schedules, especially to the FI schedule. These results demonstrate that humans discriminated the FI schedule and suggest that human schedule insensitivity is due to other than discriminative properties of the schedules.