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The generalized matching law, that organisms divide their time between alternatives in proportion to the value of the reinforcement consequent on the choice, is derivable from the assumption that an organism choosing between alternatives is under no constraints except those the contingencies of reinforcement impose. Hence, the law is not subject to empirical test. Its value lies in its simple codification of assumptions underlying choice experiments.

Bats of the species Phyllostomus hastatus were trained to press a pigeon key with food as the reinforcer. Patterns of responding under fixed‐ratio, fixed‐interval, and variable‐interval schedules of reinforcement were similar to those typically shown by other species. In a simple auditory discrimination, responding readily came under stimulus control. It is suggested that the behavioral method could be applied to various problem areas of bat behavior.

The present experiment sought to develop a reliable procedure for measuring visual acuity in non‐verbal retarded children. Five non‐verbal retarded children and two literate adults were examined. The two adults were included in the experiment so that verbal communication with them could validate certain assumptions regarding the experimental procedures. By utilizing a lever press as the criterion response signifying a visual discrimination and employing the Snellen “E” discriminanda, a reliable subjective measure was obtained, not unlike those measures taken from verbal adults. Contrary to several antecedent procedures, a relatively precise measurement of subjective acuity was shown to be obtainable from non‐verbal retarded children. Additionally, the procedure was successful in evaluating the effectiveness of prosthetic lenses previously prescribed for two of the children.

The definition of an operant as a response class each of whose members possesses the property upon which reinforcement is contingent is not broad enough to cover the units that are supposed in Skinner's accounts of extinction, superstition, and transfer of learning. A broader definition is suggested. Finally, properties defining operants are discussed.

Pigeons, previously trained to peck a key (using food as the reinforcer), were permitted unlimited access to food and, concurrently, key pecking was allowed to go unreinforced until all pecking ceased. A tone ending with electrical shock was then repeatedly presented in an effort to establish the tone as a potentially suppressing stimulus. When key pecking was later reestablished, tone presentation (without shock) sharply reduced the rate of pecks. At selected points throughout the experiment, special observation procedures supplemented the recordings of key pecks and provided detailed fine‐grain protocols of the birds' overt movements during the periods before, during, and after tone presentations. Results indicated that neither punishment of key pecks nor punishment of other overt movements was a necessary precursor to the conditioned suppression observed in the final stage. As such, the findings support interpretations of conditioned suppression that characterize the phenomenon as reflecting a conditioned emotional reaction that either directly or indirectly inhibits overt activity.

Pigeons were exposed to two keys, a main key and a changeover key. Initially non‐differential training was given in which pecking the main key was reinforced on a variable‐interval 2‐min schedule when the key displayed the first stimulus, a black line on a blue background, and was reinforced on an identical but independent variable‐interval 2‐min schedule when the key displayed a plain blue stimulus. Later, differential training was given in which pecking the main key was reinforced on a variable‐interval 2‐min schedule when the first stimulus was displayed; and was reinforced on a variable‐interval 10‐min schedule when a second stimulus, a black line of another orientation on a blue background, was displayed. During non‐differential and differential training, each peck on the changeover key changed the stimulus on the main key. Generalization tests were given before and after the differential training. These consisted of presentations on the main key of seven orientations of the black line on the blue background, including the first and second stimuli, with no reinforcements being given. Changeover‐key pecks changed the stimuli on the main key. Generalization gradients were obtained using three measures: time spent, responses, and response rate in the presence of each test stimulus. Typically, maximum values on these measures occurred to stimuli away from the first in a direction opposite the second stimulus, and minimum values occurred to stimuli away from the second in a direction opposite the first.

Twenty to seventy per cent of the reinforcements scheduled for pigeons' fixed‐ratio 80 performances were replaced by a 4‐sec timeout. Pauses after reinforced ratios were unchanged at 80% reinforcement, but were lengthened at lower reinforcement percentages. Pauses after nonreinforced ratios were shorter than post‐reinforcement pauses. When 50% of the reinforcements arranged by a variable‐interval 60‐sec schedule were replaced by a 4‐sec timeout, pauses after reinforcement omission increased. Both frustrative nonreward and reinforcement aftereffects notions can explain the fixed‐ratio results; neither easily explains the variable‐interval data.

During a brief conditioned stimulus (15 or 30 sec) that terminated with the response‐independent delivery of banana pellets, operant responding reinforced by other food pellets according to a variable‐interval schedule of reinforcement was suppressed in the squirrel monkey. Conditioned stimuli of longer duration (1, 2, and 3 min) did not reliably affect the rate of operant performance. Brief conditioned stimuli generated homogeneous response patterns of nearly complete suppression. Increasing the CS duration did not enhance responding, as previously reported, but led to alternate bursting and pausing, which suggested a loss of control by the conditioned stimulus. The results suggest that the magnitude of “positive” or “negative” conditioned suppression reflects the strength of the classical conditioning process.

Three pigeons were studied under two‐key concurrent variable‐interval schedules with food as the reinforcer on one key and ectostriatal brain stimulation as the reinforcer on the other. Brain‐stimulation parameters were kept constant while the rate of food reinforcement availability was varied. The results showed that qualitatively different reinforcers could be handled in the same theoretical framework that applies when choice is between different rates, immediacies, and amounts of a single reinforcer.

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