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In Exp. I, shallow U‐shaped gradients of inhibition in the line‐orientation dimension were obtained from birds that had a vertical (0°) line on a green surround correlated with extinction and a blank green surround correlated with reinforcement. Birds that had massed extinction in the presence of the 0° line showed flat gradients. Thus, discrimination training, but not massed extinction, appears to generate inhibitory control. In Exp. II, as in studies of control by a stimulus correlated with punishment, non‐differential training across the line‐orientation dimension preceded further sessions. Steep inverted gradients about the 0° line were obtained after discrimination training with the 0° line correlated with extinction. Gradients obtained after massed extinction tended to be flat. Again, discrimination training was critical in obtaining negative gradients of stimulus control.

In squirrel monkeys responding under a schedule in which responding postponed the delivery of electric shock, the presentation of response‐dependent shock under a fixed‐interval (FI) schedule increased the rate of responding. When the schedule of shock‐postponement was eliminated, so that the only shocks delivered were those produced by responses under the FI schedule, a pattern of positively accelerated responding developed and was maintained over an extended period. When responses did not produce shocks (extinction), responding decreased. When shocks were again presented under the FI schedule, the previous pattern of responding quickly redeveloped. In general, response rates were directly related to the intensity of the shock presented, and inversely related to the duration of the fixed‐interval. These results raise fundamental questions about the traditional classification of stimuli as reinforcers or punishers. The basic similarities among FI schedules of food presentation, shock termination, and shock presentation strengthen the conclusion that the schedule under which an event is presented and the characteristics of the behavior at the time the event is presented, are of overriding importance in determining the effect of that event on behavior.

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Six subjects, comprising one class at a school for the deaf, were given reinforcement consisting of time free from school work for remaining seated in the classroom. As a result, the frequency of leaving their chairs was sharply reduced. A second procedure presented free‐time not contingent on remaining seated. Little change was seen in the already lowered response rate. An extension of the time required to be seated with corresponding reduction in the number of daily free‐time periods did not reduce the effectiveness of the procedure. A one‐day observation after six weeks indicated that the procedure was still effective. A one‐day contingency reversal, requiring subjects to leave their chairs at least once during each seated period in order to receive free‐time, substantially raised the frequency of out‐of‐seat responses.

Fighting rates between paired rats were investigated as a function of the probability of attack by a single animal. Animals from stable high‐fighting and low‐fighting frequency pairs were intermatched to detect individual high‐fighting and low‐fighting rats. Pairs of high‐fighting animals then received saline or different chlorpromazine dosages during successive sessions. Finally, single high‐fighting members of each pair also received the different drug dosages. The chief findings were that: (a) rats showing high fighting rates when matched against each other revealed low fighting rates when matched against one, but not the other member of a low‐fighting pair; and (b) high‐fighting rats decreased their fighting rates as their own or their opponent's chlorpromazine dosage increased. These results indicated that a low rate of fighting on the part of one rat results in a low fighting rate on the part of its opponent.

When the lever‐pressing behavior of five rats was maintained by a DRL schedule (reinforcement was scheduled only when a specified waiting time between successive responses was exceeded), collateral behavior developed that apparently served a mediating function. In two cases this behavior did not arise until the experimental environment included pieces of wood that the rats started to nibble. When collateral behavior first appeared, it was always accompanied by an increase in responses spaced far enough apart to earn reinforcement. If collateral behavior was prevented, the number of reinforced responses always decreased. Extinction of lever pressing extinguished the collateral behavior. Adding a limited‐hold contingency to the schedule did not extinguish collateral behavior. It appears that the rat can better space its responses appropriately when concurrently performing some overt collateral activity. The amount of this activity apparently comes to serve as a discriminative stimulus. To assume the existence of internal events that serve as discriminative stimuli in temporal discriminations is, at least under some circumstances, unnecessary.

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