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Rats trained to lever‐press with spreading depression in one cerebral hemisphere showed weak responding when tested with depression shifted to the trained hemisphere. The rats were then divided into two groups: one group (normal) was permitted a single reinforced response with neither hemisphere depressed, the other group (depressed) was permitted a single reinforced response with the trained hemisphere depressed; both groups were then tested with the trained hemisphere depressed. Responding during this second test increased for both groups, but the magnitude of the increase tended to be greater for the depressed than for the normal group. Since memory transfer could not have occurred with the trained hemisphere depressed, the results were taken to indicate that the single reinforced response strengthened stimulus generalization between train‐test conditions.

Three of four white rats learned to press first one bar and then another to escape or avoid electric shocks. Cumulative bar‐holding‐time records showed that holding occurred frequently on the second bar but hardly ever on the first, indicating that bar‐holding is more “perserverative” than “preparatory”. The response chain, first‐bar press second‐bar press, was more easily established by a forward than by a backward chaining procedure.

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Rate of response under a free‐operant avoidance procedure decreases as the response‐shock interval increases. The present experiment demonstrated an inverse relation between rate of response and lever‐holding time. An invariance was found in the total time per session that a subject was in contact with the lever. It is suggested that lever‐holding behavior may be as sensitive as response rate to changes in the response‐shock interval.

Eight white rats were trained to make fixed numbers of responses on each of two bars alternately in the presence of different exteroceptive stimuli. Three types of error were observed: alternating—bar switching before response requirements for reinforcement were met; perseverating—responding on the wrong bar after reinforcement; and overshooting—responding on a bar after reinforcement became available. Alternating and perseverating errors occurred mainly on the bar requiring the smaller ratio. When the ratios on the bars were changed, alternating errors were most common, but they diminished rapidly. Perseverating and overshooting errors did not diminish.

The introduction of a warning signal that preceded a scheduled shock modified the temporal distribution of free‐operant avoidance responses. With response‐shock and shock‐shock intervals held constant, response rates increased only slightly when the response‐signal interval was reduced. The result is consistent with Sidman's (1955) findings under different conditions, but at variance with Ulrich, Holz, and Azrin's (1964) findings under similar conditions. Methylphenidate in graded doses increased response rates, modifying frequency distributions of inter‐response times. Drug treatment may have disrupted a “temporal discrimination” formed within the signal‐shock interval. More simply, methylphenidate influenced response rates by increasing short response latencies after signal onset; this effect was more prominent than the drug's tendency to increase the frequency of pre‐signal responses. When signal‐onset preceded shock by 2 sec, individual differences in performance were marked; methylphenidate suppressed responding in one rat as a function of increasing dose levels to a greater degree than in a second animal, but both subjects received more shocks than under control conditions.

A procedure is described for assessing response bias to either the form or color dimension of a compound standard stimulus. Responding was assessed under conditions of equal reinforcement (three tokens) for responding to either the form or color dimension. Under these conditions, the four male subjects (aged 7 to 11 yr) differentially responded to the form dimension. After a bias was assessed, the number of tokens delivered contingent upon form responses was reduced. After a reversal in differential responding, the equal‐reinforcement condition was reintroduced. Two of the subjects returned to their initial response bias when equal reinforcement for either dimensional response was reintroduced, and two maintained the reversal established during the differential‐reinforcement phase. For the latter two subjects, differential reinforcement was again imposed, in favor of form. This partial replication reinstated their original pattern of response bias.

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