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Pigeons learned to peck a green key on which parallelogram‐shapes were projected; they then received generalization tests in which the orientation of the parallelogram was varied. Nondifferential training produced very little eventual stimulus control along the orientation dimension, but when training included S– trials (absence of the parallelogram) subjects responded consistently more to certain orientations than to others. Unlike typical results for visual generalization (e.g., line‐tilt), the tilt gradients obtained for this complex stimulus were bimodal, supporting predictions on the basis of human perceptual data. However, unimodal gradients could be produced by specific discrimination training along the orientation dimension. Other forms of intradimensional training also produced relatively steep gradients, often characterized by unexpected but consistent secondary peaks. An attempt to obtain inhibitory gradients (S+: green key; S–: parallelogram on a green background) resulted in virtually zero responding all along the shape‐orientation dimension; therefore, specific inhibitory control could not be evaluated. All these experiments suggest that definition of this complex stimulus dimension in terms of mere “angular orientation” is inappropriate, and alternative interpretations are discussed.

Five groups of pigeons received seven sessions of variable‐interval reinforcement for pecking a blank white key, followed by either 1, 2, 4, 8, or 16 sessions of training on a successive discrimination in which the positive stimulus was the blank white key and the negative stimulus was a black vertical line on the white key. After training, a generalization test was administered along the line‐tilt continuum. Relative gradients of inhibition became steeper with increased amounts of training, and reliably nonhorizontal absolute gradients were obtained only from groups of subjects with at least four days of training. Therefore, inhibitory stimulus control improves with added training. Several problems with the concept of “inhibition” are examined and some implications of the results for theoretical analyses of operant discrimination learning are discussed.

Response‐contingent electric shock was evaluated in a laboratory and criterion situation before using it to eliminate infrequent and unpredictable biting and destructive acts from the repertoire of a retarded adolescent. Although the initial results were dramatic, the effects of shock were highly discriminated and the therapeutic objectives were not accomplished. The study demonstrates the power and some limitations of shock punishment and is presented so that others will be better prepared for problems that may arise before the goals of a program involving shock punishment will be realized.

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Pigeons were trained to respond under two conditions with two identical variable‐interval schedules of positive reinforcement. While the schedules operated for separate response keys, they were not available concurrently. During one condition, each response was punished with electric shock. During the other condition, shocks were delivered independently of responding. The punishment suppressed responding but the free shocks did not. However, when allowed to choose, the pigeons preferred the condition associated with the lowest rate of shock regardless of whether or not the shock was dependent on responding. In general, shocks exerted their greatest effect on whichever response had the greatest influence on shocks. In this respect, punishment is instrumental in suppressing behavior and the properties of punishment are symmetrical to those of reinforcement. This empirical symmetry dictates a corresponding conceptual symmetry in terms of a positive law of effect accounting for response increments and a negative law accounting for response decrements.

The resistance of responding to extinction after variable‐interval reinforcement in one of two components of a multiple schedule of reinforcement was (1) greater, when responding in the second component was reinforced on a variable‐interval schedule than when responding there was extinguished, (2) not reduced, by a more rapid decrease in the rate of responding than occurs in ordinary extinction in the second component, and, (3) increased, by the occurrence of positive behavioral contrast before the beginning of extinction.

Systematic reinforcement procedures were used to increase study behavior in the classrooms of three beginning teachers experiencing problems of classroom control. Classroom study rates were recorded during a baseline period. During subsequent experimental periods, the teachers changed one or more reinforcement contingencies (teacher attention, length of between‐period break, a classroom game) to bring about increased study rates and concomitant reductions in disruptive behaviors. A brief reversal period, in which these contingencies were discontinued, again produced low rates of study. Reinstatement of the contingencies resulted once again in marked increases in study behaviors.

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