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A procedure developed earlier (Terrace, 1963) successfully trained a red‐green discrimination without the occurrence of any errors in 12 out of 12 cases. Errorless transfer from the red‐green discrimination to a discrimination between a vertical and a horizontal line was accomplished by first superimposing the vertical and the horizontal lines on the red and green backgrounds, respectively, and then fading out the red and the green backgrounds. Superimposition of the two sets of stimuli without fading, or an abrupt transfer from the first to the second set of stimuli, resulted in the occurrence of errors during transfer. Superimposition, however, did result in some “incidental learning”. Performance following acquisition of the vertical‐horizontal discrimination with errors differed from performance following acquisition without errors. If the vertical‐horizontal discrimination was learned with errors, the latency of the response to S+ was permanently shortened and errors occurred during subsequent testing on the red‐green discrimination even though the red‐green discrimination was originally acquired without errors. If the vertical‐horizontal discrimination was learned without errors, the latency of the response to S+ was unaffected and no errors occurred during subsequent testing on the red‐green discrimination.

Superstitions were demonstrated with human subjects when presses on one button were reinforced on a VI 30‐sec schedule while presses on a second were never reinforced. Superstitious responding, on the second button, was often maintained because presses on that button were frequently followed by reinforcement for a subsequent press on the first button. The introduction of a changeover delay (COD), which separated in time presses on the second button and subsequent reinforced presses on the first button, reduced or eliminated the superstitious responding of these subjects. Some complex superstitions were also demonstrated with other subjects for which the COD was in effect from the beginning of the session.

Rats were trained to escape from shock by pressing a bar. Bar holding was subsequently punished with very brief shocks. This treatment failed to depress bar‐holding behavior. In some cases, although the escape shocks were delivered very infrequently, bar holding was maintained and resulted in the delivery of several thousand punishments per session. These and other effects of the punishment treatment were investigated. Finally, some of the possibilities of superstitious escape responding were explored by presenting inescapable shocks to rats that had been trained to escape shock by lever pressing. Although responding during these shocks had no programmed consequences, responding was sustained.

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The performance of two monkeys, on fixed‐interval schedules, was examined with a visual, an auditory and a combined auditory‐visual clock. The clock, a voltmeter and/or a variable frequency tone, produced performances different in many aspects from those recorded earlier with pigeons. Instead of the sustained high rates of responding at the optimal settings of the clock, the monkeys' rates of responding were often extremely low even though a limited‐hold contingency was utilized.

Escape responses of squirrel monkeys were reinforced according to a fixed‐ratio schedule. The reinforcement was a period of safety from a stimulus that signalled the delivery of intermittent pain‐shocks. When the frequency of shock was gradually reduced, the performance remained at a high level until the shocks were quite infrequent. Similarly, the duration of the period of safety could be reduced to a few seconds with little loss of behavior. Thus, the responses appeared to be reinforced by even a brief period of safety, the actual degree of shock reduction being fairly slight. The changes in responding during this fixed‐ratio escape procedure were comparable to the response changes typically obtained during fixed‐ratio food procedures.