LEARNING BY DOING THROUGH PROGRAMMED INSTRUCTION.
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F MECHNER
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A fixed interval schedule in which the interval is initiated by a response.
The fixed interval schedule described requires the animal to initiate every time interval by making a response on a bar other than the one on which it is reinforced. This response, R(A), demarcates the postreinforcement pause (S(R)-R(A) interval) from the fixed interval pause (R(A)-R(B) interval) so that these pauses may be measured separately. Twelve rats and three monkeys, working in two-bar Skinner boxes, were trained and stabilized on this schedule. The resulting performances, presented for individual animals, are analyzed in terms of (1) the relative frequencies with which the animal waits various lengths of time between consecutive responses, (2) the relative frequencies with which various rates of responding appear, (3) the change in response rate throughout the fixed interval, (4) the average length of the postreinforcement pause, (5) the relative frequencies with which the animal waits different lengths of time between the R(A) and the first R(B), and (6) the average inter-response time as a function of the rank order in the fixed interval of the inter-response time. The joint interpretation of the several measures taken leads to the following conclusions: 1. The probability of an R(B) increases throughout the fixed interval. 2. The increase is discontinuous at the first R(B), at which point the probability increases sharply. 3. The frequency distributions of R(A)-R(B) pauses exhibit three discrete types of behavior with no intermediate cases. 4. The (main) mode of R(A)-R(B) interval length usually occurs just below the fixed interval requirement.
Animals↗
Behavioral effects of caffeine, methamphetamine, and methylphenidate in the rat.
It was possible to distinguish three closely-related psychomotor stimulants, caffeine, methamphetamine, and methylphenidate, by means of two operant behavior procedures, fixed interval and fixed number. Under the fixed interval procedure, the percentage change in the number of R(B)s per reinforcement was significantly smaller with caffeine than with methamphetamine or methylphenidate (p < .001). Under the fixed number procedure, the percentage change was significantly smaller with methamphetamine than with caffeine or methylphenidate (p < .001). Thus, methylphenidate had a methamphetamine-like effect under fixed interval and a caffeine-like effect under fixed number.
Animals↗
Effects of deprivation upon counting and timing in rats.
Two procedures were used in an investigation of the effects of deprivation upon counting and timing. Under the first procedure, fixed minimum interval (FMI), the rat received liquid reinforcement every time it pressed bar B after having waited a minimum of 5 sec following a press on bar A. Under the second procedure, fixed consecutive number (FCN), reinforcement was delivered every time the rat pressed bar B following a run of at least four consecutive responses on bar A. Water deprivation was varied over a set of values ranging from 4 to 56 hr. Deprivation had almost no effect on the waiting time in the FMI procedure, or on the number of responses per run in the FCN procedure. With both procedures, increasing deprivation shortened the pause between reinforcement and the next response. In the FCN procedure, the speed with which the runs were executed increased with increasing deprivation, although the number of responses in these runs was relatively unaffected.
Animals↗