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Schedules of intermittent brain‐stimulation reinforcement have been shown to maintain performances when a reinforcement is defined as several response‐produced, brief trains of stimulation. The present experiments show that the number of response‐produced trains permitted per reinforcement is a variable analogous to amount or magnitude of reinforcement in the conventional food‐reinforcement experiment. Systematic effects were obtained when that variable was manipulated within a multiple schedule and also on variable‐interval schedules programmed concurrently.

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Most current commercial devices dispense dry food pellets by moving the pellets horizontally toward a discharge point. Individual pellets, captured by perforations in a horizontal metal disk, are discharged one by one by stepwise rotation of the disk within the pellet reservoir. In our laboratory, where the average pellet discharge rate is some 20,000 pellets per week, feeders of this type produced occasional problems. Some were electronic; others involved failure always to capture a pellet in each perforation, particularly when the pellet supply was low. But the most common problem was an accumulation of pellet chips and dust under and around the perforated disk, which ultimately jammed the mechanism. Despite weekly cleaning and maintenance, troubles arose at least twice a month, prompting a search for a simpler pellet‐feeder design which would be more reliable and require less maintenance. The present pellet feeder employs a vertical rather than horizontal design principle. It has been used extensively in operant conditioning applications for more than a year. More than 200,000 pellets have been reliably discharged from a single feeder without a breakdown. No maintenance, other than a weekly cleaning of the discharge tube, has been required.

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Pigeons were trained to discriminate the presence or absence of a vertical line, and their performance on a subsequent generalization test was compared with that of other pigeons trained to discriminate a vertical from a 45° line. On the generalization gradient after discrimination training, the presence/absence discrimination group showed a peak at 0° (vertical) while the peak for the 0°/45° discrimination group shifted from 0° in a direction away from the 45° line. The results, discussed in connection with a recent suggestion about the role of color in the peak‐shift effect, are interpreted as supporting the generality of the phenomenon.

A method was developed for studying the reactions of rats to aversive shock. The distinctive features were the design of the chamber and a method of restraint that allowed the use of surface electrodes to deliver the shock. Advantages of this method were: (1) accurate specification of the shock actually received by the rat; (2) elimination of all unauthorized escape or avoidance reactions; (3) elimination of the shock scramblers and floor grids required with foot‐shock; and, (4) rapid acquisition of performance under various avoidance procedures and various frequencies of shock delivery.

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