The purpose of this paper is to review the researches on stimulus equivalence in nonhuman animals, based on the formulation by Sidman. Among the behavioral properties that he proposed as essential elements of stimulus equivalence, “reflexivity” has been confirmed in various species, and the evidence of “transitivity” has also been obtained in pigeons. However, “symmetry” seems much more difficult to be formed, and specifically, “equivalence” was shown only in a sea lion. On the other hand, stimulus equivalence also has been examined using procedures other than traditional conditional discrimination, or by many-to-one (MTO) matching-to-sample and Pavlovian conditioning. Recently, positive evidence was obtained in budgerigars, based on the interpretation that behavior, in addition to stimulus, should be included as a member of an equivalence class. These new approaches in research have suggested that equivalence may not be a behavioral ability that enables us to use language, but a basic cognitive function common to other animals. This proposition, indicating that equivalence is apt for comparative study, implies that the conventional research methods should be reexamined.

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We conducted two experiments in order to investigate whether the presentation of food contingent on the imprinted responses could maintain these responses in chicks. In the first experiment, the presentation of food was contingent on the chicks' imprinted responses. Due to this contingency, chicks could maintain their imprinted responses as long as they received the contingency. In the second experiment, the presentation of food was contingent on either the chicks' non-imprinted responses or the chicks' responses directed towards the novel object. On these contingencies, the chicks' imprinted responses were rapidly extinguished. The results of the two experiments suggest that the contingency of food reinforcement may reflect the natural contingency of imprinting in chicks and contribute to the irreversibility of imprinting.

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We developed a new method of drug administration for planaria. A syringe fixed to a microinjector was connected to an injection needle with a flexible vinyl tube. This flexible tube helped to guide the needle to the exact administration point of the body. A precise amount of drug can be administered by the operation of the microinjector. We obtained a dose-response curve of immobilization after urethane administration (400 mg/kg-3200 mg/kg). Stable immobilization was observed after 1600 mg/kg administration, and the average duration of immobilization was 8 min. The effective dose 50% (ED₅₀) estimated by the interpolation of the data between 800 mg/kg and 1600 mg/kg groups was 933 mg/kg.

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In the classical conditioning, the temporal relationship between a conditioned stimulus (CS) and an unconditioned stimulus (US) has an effect on the strength of elicited conditioned responding (CR). The present study explored the effect of temporal relationship between a first-order CS (CS1) and an US on CR to the CS1 and a second-order CS (CS2) in rats' conditioned licking suppression. Strong CR was elicited by the CS1 in groups where the CS1 was presented before the US, weak CR in a group where the CS1 and the US were presented simultaneously, and little CR in groups where the CS1 was presented after the US. The amount of CR to the CS2 was monotonously corresponded to the amount of CS1-elicited CR. These results were different from those of recent studies.

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A new model of the MPP (multistimulus, portable, and programmable) conditioning panel for pigeons is described. The two-response-key MPP panel originally developed by J. D. Delius and his collaborators (Xia, Delius, & Siemann, 1996) allows pigeons to perform in their familiar home cages. Stimuli are presented on the horizontal plane with light-emitting diode matrices. Food rewards are dispensed directly onto the stimulus display and the response location. Our new panel is designed to attain highly reliable food-dispenser function and to increase the range of stimuli and discrimination procedures available. Visual stimuli are presented with a miniature LC monitor affixed under the horizontal platform. Two different types of platforms, one contains a single rectangular key and the other has two side-by-side keys, are replaceable. Two experiments (a two-choice discrimination task and a go/no-go discrimination task) demonstrated the effectiveness of the system.

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We are developing a computer-based visual display system for behavioral experiments with pigeons. This system consisted of a 14 inch color CRT monitor and an experimental chamber with three clear response keys mounted on the transparent key panel. Three color circles were presented on the screen of the monitor, which corresponded to each of the three response keys. The monitor was placed behind the front panel of the chamber so that each stimulus presented on the screen of the monitor could be viewed from any position through the transparent key panel. In this system, a keypecking response was successfully shaped by the method of successive approximations and the pecking response could be well maintained under various procedures such as successive discrimination and delayed matching-to-sample tasks.

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Demand curves for food consumption by 2 pigeons were examined under 4 unit prices (cost-benefit ratios) manipulated by 4 fixed-interval (FI) schedules with reinforcement durations of 3-s or 6-s arranged so that each FI value in the 6-s condition was double that of the 3-s condition. Session lengths were 1.5-, 3.0-, or 4.5 hours. Time cost in each reinforcement condition increased every 6 sessions for each session length. A new session was randomly chosen after the highest price. Demand curves fitted to the 8 data points for each session length (using Equation 4 of Hursh et al., 1988) show the expected positively decelerating function. Although some deviations were found at the highest price in one pigeon, variance accounted for exceeded 95% in all cases indicating that cost and benefit factors are functionally equivalent. Session length did not have a systematic effect on the parameters of these fitted equations. An increase of parameter value indicating elasticity, however, was found in 1.5-hour session for one pigeon.

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