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Pigeons' key pecks were both punished with electric shock on four‐component chained and tandem fixed‐interval schedules and reinforced on a variable‐interval schedule of food presentation. Pecking was suppressed less in the early components of the chained schedule than in the early components of the tandem schedule. Related multiple and mixed schedules of punishment were also presented; these schedules were identical to the chained and tandem schedules, respectively, except that components changed independently of responding. Similar effects were obtained, in that responding was suppressed in all components of the mixed schedule and only in the fourth component of the multiple schedule of punishment. The performances maintained on the chained and tandem schedules of punishment were generally symmetrical to those found in analogous chained and tandem schedules of food reinforcement.

Three pigeons were studied under a pair of equal fixed‐ratio schedules and a pair of equal variable‐ratio schedules. Each pair was arranged as independent, concurrent schedules and also in a non‐independent relation where each peck in a schedule counted toward the response requirement of both schedules. The non‐independent pair of variable‐ratio schedules maintained much higher changeover rates than any of the other three arrangements. Thus, two factors seemed necessary for generating high changeover rates. Responding on a schedule had to count toward the response requirement of both schedules, and the component schedules had to be variable. These data are consistent with the hypothesis that changeovers are at least partly controlled by the probability of reinforcement following a changeover.

Ethological recording procedures measured collateral behavior in pigeons whose key‐pecking performance was suppressed during a tone that ended with unavoidable electric shock. Independent recordings of gross behavior were made by two observers throughout 60‐sec intervals immediately before, during, and after tone presentation. Results indicated significant reductions in the frequency of collateral movements and an increase in the time between successive movements during tone presentations. These effects were observed in all subjects, despite differences in the sequential patterns of behavior. Only partial recovery of the behavior evidenced before tone presentation was found during a 60‐sec interval following shock. It was concluded that conditioned suppression procedures caused the bird to “freeze” during tone presentation and in this fashion produced a general inhibitory effect on ongoing overt activity, including key pecking.

Pigeons were trained on a non‐spatial delayed alternation task in which the correct stimulus was that color not responded to on the preceding trial. Subjects required to emit either 15 or 30 pecks to the correct stimulus within a trial learned the task, those required to emit only one or five pecks did not. Also, alternation was learned more easily after an incorrect than after a correct trial. Later experiments showed that a minimum fixed‐ratio value was required for successful color alternation to occur, even though no fixed‐ratio requirement was necessary when a position cue was available. The mechanism of the fixed‐ratio effects derived from the pigeons' tendency to repeat their response in the presence of the color reinforced on the last trial. Whereas subjects trained on larger fixed‐ratios corrected this error tendency within a trial, subjects trained on smaller fixed ratios did not.

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Six pigeons were trained to match wavelengths in a three‐key matching‐to‐sample paradigm. Test trials were occasionally presented, where probe wavelengths appeared on the center key and choices were made to the training stimuli presented on the side keys. Color naming functions were obtained by plotting the percentage of test trials that each training stimulus wavelength was chosen for each center key probe wavelength. The wavelength where the functions intersected was interpreted as a transition point between pigeon hues. Three experiments employed different wavelengths as training stimuli. The first two experiments demonstrated that the intersection of the color‐naming functions occurred in all cases at 540 nm and 595 nm. The third experiment employed 540 nm and 595 nm as two of the three training stimuli, and the relatively slow acquisition, together with the resulting color‐naming functions, supported the proposition that 540 nm and 595 nm may be transition point wavelengths between pigeon hues.

Four rats received water on a fixed‐ratio schedule for lever pressing in the presence of a tone (or light) stimulus and on a variable‐interval schedule in the presence of a light (or tone) stimulus. Following stabilization of a high response rate during the fixed‐ratio component and a moderate response rate during the variable‐interval component, brief periods with the light and tone presented simultaneously but with no responses reinforced were inserted into the regular training schedule. Response rates during the compound stimuli were intermediate between the response rates controlled by the individual fixed‐ratio and variable‐interval associated stimuli.

Rats' responding was maintained by fixed‐interval schedules of reinforcement in the presence of a tone or two separate lights. The lights were either of low, moderate, or high intensity. Compounds of these single discriminative stimuli each maintained a greater frequency of response than did the single stimuli, and the compound composed of stimuli from different sensory modalities (light + tone) maintained a greater level of responding than did the compound composed of stimuli from the same sensory modality (light + light). Combining lights of different intensity had no differential effect on responding. However, in the second experiment, a compound composed of a light and a tone, each of greater intensity than the light and tone of another compound, initially maintained a higher frequency of response, demonstrating intensity effects during stimulus compounding when the increase in intensity occurs through the component stimuli. This intensity effect, however, was only transitory.

Pigeons' key‐pecking responses were maintained under concurrently available variable‐interval schedules of reinforcement. Responses in the presence of two different key‐colors were reinforced on two independent and concurrent variable‐interval schedules of food reinforcement, each associated with one of the key colors (red or green). Pecks at a second key (changeover key), always white, would alternate the colors on the main key. In Exp. 1 and 2, electric shock of 50 msec duration followed immediately after changeovers. The proportion of responses in the presence of the color associated with the higher frequency of reinforcements per hour was a direct function of shock intensity contingent on changeovers. When both schedules provided equal number of reinforcements per hour, there was no systematic effect of shock intensity on response distribution. In Exp. 3, a timeout period was contingent on changeovers, and response distribution was a function of timeout length.

Pigeons' pecks were maintained on concurrent variable‐interval 1‐min variable‐interval 3‐min schedules of reinforcement, with a changeover delay of 2 sec. When changeover delay was increased successively to 5.0, 7.5, and 12.5 sec (Exp. I) the actual relative rate of reinforcement for the variable‐interval 3‐min key decreased progressively for two birds, abruptly for two other birds, and the subjects devoted proportionately less of their time and responding to that key. However, the relative performance measures (relative time and relative responding) approximated the actual relative rate of reinforcement, with a maximum discrepancy of 11%, over all changeover delay values investigated. Experiment II attempted to lengthen response‐run durations on the variable‐interval 3‐min key so that they were long enough to meet the changeover delay requirement at each new changeover delay value, by progressively increasing the changeover delay by 0.5‐sec increments. With this procedure the actual relative rate of reinforcement approximated more closely the scheduled relative rate as changeover delay increased. As in Exp. I, relative performance measures approximated the actual relative reinforcement rate (maximum discrepancy 17%).