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During training sessions, pecks by pigeons on a response key illuminated by a vertical line of white light resulted in reinforcement and an ensuing blackout according to a fixed‐interval schedule. Training sessions were followed by dimensional stimulus control test sessions during which the orientation of the line present throughout the fixed interval was varied. Inverted U‐shaped (excitatory) gradients of responding, with maximum responding occurring in the presence of the vertical line, were observed during the terminal part of the fixed interval. U‐shaped (inhibitory) gradients of responding, with minimum responding occurring in the presence of the vertical line, were observed during the early part of the fixed interval when the preceding interval had terminated with reinforcement and blackout but not when the preceding interval had terminated with blackout only. These results suggest that the dimensional control by the stimulus present throughout the fixed interval is of a conditional variety. Whether the fixed‐interval stimulus exerts inhibitory or excitatory dimensional control depends upon the presence and absence, respectively, of stimuli associated with reinforcement.

Applied researchers increasingly report the use of paraprofessionals to implement key program components. However, despite such apparent advantages as increased availability and lower salaries, problems in maintaining acceptable levels of on‐the‐job performance in these workers have been reported. This study assessed the effects of a supervisory package on the work behavior of five paraprofessional tutors in a remedial reading program. The package consisted of written handouts and instructions, tests of tutor understanding, a video tape, mention of tutor performance by supervisors, and publicly posted feedback on work performance. One randomly chosen tutor received feedback each day on (1) his degree of completeness in tutoring one student's answers to comprehension‐check questions, (2) his accuracy in tabulating that student's data sheet, and (3) his promptness in beginning the first student's tutorial session. The supervisory package produced marked improvement in completeness, some improvement in accuracy, but no improvement in promptness. Application of the supervisory package seemed practical, as an average of nine daily tutorial sessions (approximately 270 min of tutoring) required a total daily average of only 28 min of supervision. It was concluded that completeness performance by nondegreed, paraprofessional tutors was closely related to the extent to which they were supervised. Despite the fact that no improvement was observed in tutor promptness, and only partial improvement was observed in tutor accuracy, the improvement to near‐perfect levels in tutor completeness suggests that further research is warranted to develop supervisory packages that might ensure the reliable and efficient use of paraprofessional workers.

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Pigeons were exposed to periodic food‐reinforcement schedules in which intervals ended with equal probability in either reinforcement or brief blackout. The effects on the pattern of key pecking of sequential probability of reinforcement, interval duration, and time to reinforcement opportunity were investigated in three experiments. The major results were: (1) at short absolute interval durations, time to reinforcement opportunity determined both postreinforcement and postblackout pause (time to first key peck within an interval); (2) at long intervals, postblackout pause was consistently shorter than postreinforcement pause, even if both events signalled the same time to the next reinforcement opportunity (omission effect); (3) when reinforcement and blackout signalled different times to the next reinforcement opportunity, within the same experiment, there was some evidence for interactions analogous to behavioral contrast.

Pigeons were trained to key peck on several multiple schedules in which the first of two components was always a simple fixed‐interval schedule. The rate of responding at the beginning of the constant fixed‐interval schedule was found to decrease with increases in the rate of reinforcement associated with the other component of the multiple schedule, but remained unchanged with decreases in the rate of responding associated with the other component. These results were interpreted as being consistent with the view that the presence and magnitude of the temporal inhibitory effects observed in a given fixed‐interval schedule are a function of the properties of reinforcing stimuli, rather than of changes in the rate of responding associated with the time interval immediately preceding the fixed interval in question.

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