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A sea lion under water performed virtually without errors on a series of three form‐discrimination reversals. Significant training requirements were the combining of a previously well‐established size cue preference with the nonpreferred form cue, followed by the gradual reduction of the size cue until it was completely eliminated. Orienting responses reached a peak and then decreased during progressive‐dimensional‐change training, suggesting critical stages in the transition of attention from the size dimension to the form dimension. Further experimentation revealed that intensive training during these critical stages obviated the need to reduce very gradually the size cue. Without special training sea lions make perseverative errors on a series of form‐discrimination reversals. “Emotional” or nontest‐oriented behavior was associated only with the occurrence of successive errors.

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The discriminative control over a spatial choice response exercised by prior behavior was studied using a procedure involving discrete exposures to a two‐member chained schedule. The initial member (red key) was either a smaller or larger fixed ratio (Mix FR:FR), the completion of which produced, after a 1‐sec delay, two white response keys. If the larger FR had been completed as the initial chain member, a single peck on the right white key was reinforced; after the smaller FR, a peck on the left white key was reinforced. Frequencies of unreinforced responses (SΔ responses) were determined with several pairs of red‐key FRs: 95‐5, 75‐25, 65‐35, 60‐40, 58‐42 and 50‐50. The SΔ response frequencies were low through the FR pair 65‐35; sharp increases were obtained with pairs 60‐40 and 58‐42. Later, curves analogous to stimulus generalization functions were obtained using a probe procedure. Finally, the delay interval between completion of a red‐key FR and the white‐key choice response was manipulated: results were variable, but SΔ response frequencies tended to increase with increasing delays.

After exposure to an avoidance schedule which included a warning signal, a rat was placed on a multiple schedule in which the first component was the same as before, i.e., a single response reset the response‐shock interval, delaying shock, and the second component differed only in that four bar‐presses were required to postpone shock. A fixed ratio requirement of four responses (FR 4) generated behavior resembling a fixed ratio requirement of one response (FR 1) since responding was controlled by the warning signal but more shocks were received. At a dosage of 2 mg/kg, methylphenidate given intraperitoneally decreased shock frequency during FR 4 periods while FR 1 behavior was not affected; at 4 mg/kg, stimulus control of avoidance responding was impaired during both components. Results at 4 mg/kg were partially confirmed by two animals exposed to an FR 4 avoidance schedule which included a warning signal but with different parameters. Response distributions showed that methylphenidate increased response rates in the absence of the warning signal, i.e., stimulus control of ratio‐avoidance behavior was impaired although the increased response rates reduced shock frequency. One hour later responses again occurred more frequently during the signal than in its absence but shocks were less frequent than during control (non‐drug) periods.

The relationship between training conditions and stimulus generalization gradients was examined using tandem schedules of reinforcement. Schedules were selected so that frequency of reinforcement and rate of responding were varied somewhat independently of each other. A peak‐shift in the generalization gradient was obtained when extinction had been associated with one of the stimuli. No comparable peak shift was obtained when there were equal response rates in the training stimuli even with dissimilar frequencies of reinforcement. The data imply that response rates at the end of training, rather than reinforcement frequency per se, determine the characteristics of the generalization gradient.

Five years ago, pigeons trained to peck a key for food were periodically presented with a 1000 cps tone which ended with electrical shock. They were then tested for the stimulus generalization of conditioned suppression. After an interruption of 2.5 yr, another series of generalization tests showed no loss of suppression. The present study was conducted 1.5 yr later to retest the effect of an extended interruption on retention of suppression. It was found, again, that suppression did not decline over time. The present paper, which summarizes the earlier data and reports the most recent findings, provides an overview of the extended behavioral consequences of the original aversive procedures administered five years ago.

Pigeons were maintained on a fixed ratio (FR 9) schedule of reinforcement for correct matching‐to‐sample responses. Included in the test situation was a vertical array of lights, illuminated in relation to the successive steps of the fixed ratio. All five subjects showed regular decrements in matching errors across the sequence of unreinforced responses within the ratio cycle. In the form of a randomly introduced probe, the stimulus situation (array of lights) appropriate to having seven of the FR 9 steps already completed was occasionally introduced at the beginning of an FR cycle. Reinforcement followed the illumination of the two remaining lights by two correct matches. The number of errors in this probe condition was sharply lower than the errors characteristic of the first two steps of the basic FR 9.

Pigeons trained to peck a key for food were periodically presented with tones ending with electrical shock until tone presentation consistently suppressed ongoing pecks. Shock was then discontinued and gradients of stimulus generalization were assessed by presenting tones with frequencies above, below, and at the frequencies of those used to develop conditioned suppression. When the training tones had frequencies at 670 and 1500 cps, resulting gradients were bi‐modal with peak suppression at 670 and 1500 cps. Of the other test tones, 1000 cps produced the most suppression. When the training tones had frequencies at 450 and 2250 cps, bi‐modal gradients were again obtained with peak suppression to the 450 and 2250 cps tones. Of the other test tones, 1000 cps produced the least suppression. These results support the hypothesis that generalized response tendencies summate.

Twenty‐four pigeons learned a successive discrimination between 500 mμ (S+) and 574 mμ (S—). When tested in extinction, some birds received stimuli around S+, with no S— presentations. These birds showed a positive peak shift, with maximum responding not at 550 mμ, but displaced to 538 mμ and 544 mμ. Other birds were tested with stimuli around S—, with no S+ presentations. These birds showed a negative shift, with least responding not at 574 mμ, but at 586 mμ. Though the first group was tested around S+ and the second around S—, total responding between groups did not differ. When retested on the other half of the continuum, however, birds that had gone from the S+ half to the S— half responded fewer times than those that had gone from the S— half to the S+ half. In a second experiment, reducing stimulus spacing from 6 mμ, to 2 mμ produced flatter gradients and decreased the amount of positive shift. In a third experiment, birds were tested across the whole continuum with stimuli presented in serial order. A sequence from 538 mμ to 586 mμ produced no responding after the first part of the session; a sequence from 586 mμ to 538 mμ produced responding throughout the session.

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