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1.
Mazur JE 《Learning & behavior》2007,35(3):169-176
Rats chose between alternatives that differed in the number of reinforcers and in the delay to each reinforcer. A left leverpress
led to two reinforcers, each delivered after a fixed delay. A right leverpress led to one reinforcer after an adjusting delay.
The adjusting delay was increased or decreased many times in a session, depending on the rat’s choices, in order to estimate
an indifference point& #x2014;a delay at which the two alternatives were chosen about equally often. Both the number of reinforcers
and their individual delays affected the indifference points. The overall pattern of results was well described by the hyperbolic-decay
model, which states that each additional reinforcer delivered by an alternative increases preference for that alternative
but that a reinforcer’s effect is inversely related to its delay. Two other possible delay-discounting equations, an exponential
equation and a reciprocal equation, did not produce satisfactory predictions for these data. Adding an additional free parameter
to the hyperbolic equation as an exponent for delay did not appreciably improve the predictions, suggesting that raising delay
to some power other than 1.0 was unnecessary. The results were qualitatively similar to those from a previous experiment with
pigeons (Mazur, 1986), but quantitative differences suggested that the rates of delay discounting were several times slower
for rats than for pigeons. 相似文献
2.
James E. Mazur 《Learning & behavior》1997,25(2):131-147
The hyperbolic-decay model is a mathematical expression of the relation between delay and reinforcer value. The model has been used to predict choices in discrete-trial experiments on delay-amount tradeoffs, on preference for variable over fixed delays, and on probabilistic reinforcement. Experiments manipulating the presence or absence of conditioned reinforcers on trials that end without primary reinforcement have provided evidence that the hyperbolic-decay model actually predicts the strength of conditioned reinforcers rather than the strength of delayed primary reinforcers. The model states that the strength of a conditioned reinforcer is inversely related to the time spent in its presence before a primary reinforcer is delivered. A possible way to integrate the model with Grace’s (1994) contextual-choice model for concurrent-chain schedules is presented. Also discussed are unresolved difficulties in determining exactly when a stimulus will or will not serve as a conditioned reinforcer. 相似文献
3.
Marcia L. Spetch Michael V. Mondloch Terry W. Belke Roger Dunn 《Learning & behavior》1994,22(3):239-251
Pigeons chose between 50% and 100% reinforcement on a discrete-trials concurrent-chains procedure with fixed-ratio 1 initial links and fixed-time terminal links. The 100% alternative always provided food after a terminal-link delay, whereas the 50% alternative provided food or blackout equally often after a delay. Additionally, the terminal-link stimuli on the 50% alternative were correlated with the outcomes in signaled, but not in unsignaled, conditions. The effects of intertrial-interval duration and length of the terminal-link delays on choice of the 50% alternative were investigated in four experiments. Preference for the 50% alternative varied with signal condition and duration of the terminal link leading to food, but not with duration of either intertrial interval or the terminal link leading to a blackout. The results are discussed in terms of conditioned-reinforcement effects, Mazur’s hyperbolic-decay model, and delay reduction. This research was supported by a Natural Sciences and Engineering Research Council of Canada research grant awarded to the first author. 相似文献
4.
In two experiments, pigeons' responding on an extraneous task was explicitly reinforced during delayed matching-to-sample
trials. In Experiment 1, red or green sample stimuli were followed by retention intervals of 0.2, 1, 4, or 12 sec, during
which pecks to a white center key were reinforced with 2.5-sec access to wheat according to extinction, variable-interval
30-sec, and variable-interval 15-sec schedules in different conditions. A proportion of .2, .5, .7, or .9 of subsequent red
or green choice responses that matched the sample were reinforced with 3-sec access to wheat. The result was that increasing
center key reinforcement, or reducing reinforcer probability, lowered overall accuracy. Initial discriminability fell, but
with no change in the rate of forgetting. In Experiment 2, initial discriminability was affected by extraneous reinforcers
that were contingent on center key pecking, but not by noncontingent reinforcers. A plausible conclusion is that initial discriminability
decreases when reinforcers strengthen competing behaviors. 相似文献
5.
Pigeons were exposed to differentially cued autoshaping trials in which conditioned stimuli were followed by food after 6 or 14 sec. Average and momentary rates of keypecking were examined on two types of unreinforced test trials: single-stimulus probe trials and simultaneous choice trials, each 40 sec in duration. Rates averaged over the 40-sec test trials did not favor the cue associated with the shorter delay to food (the short-delay cue) on either type of test trial; however, average rates prior to the scheduled time of food delivery were reliably higher for the short-delay cue on choice trials. Momentary rates of keypecking during choice trials varied as a function of both cue and elapsed time from trial onset. At short elapsed trial times, rate of pecking was higher for the short-delay cue, with this difference reversing at longer times. A reversal of the programmed relation between key color and delay to food presentation for 5 birds confirmed the generality of these findings. Implications of these data for models of Pavlovian conditioning and for methods of assessing conditioned response strength are discussed. 相似文献
6.
Jay Moore 《Learning & behavior》1976,4(4):441-450
Pigeons responded on a two-key concurrent chains choice procedure with the same level of percentage reinforcement on each key. During the initial links, a choice response on either key occasionally produced a conditioned reinforcer—which on one key was associated with a 15-sec, and on the other key with a 30-sec, interreinforcement interval—or an extinction stimulus. In Part 1, the initial links were equal. With successive decreases in the probability of a reinforcer, choice shifted from preference for the 15-sec terminal link toward indifference. In Part 2, the initial links were unequal and were arranged so that the shorter initial link preceded the 30-sec terminal link. At a high probability of a reinforcer, the pigeons again preferred the 15-sec terminal link. However, at a low probability, the pigeons reversed and preferred the alternate key. It was concluded that the conditioned reinforcers tended to become functionally equivalent at a low probability of a reinforcer, despite the nominally different interreinforcement intervals, with the result that choice was then modulated by the relative size of the initial links. The data are inconsistent with the view that choice and the strength of conditioned reinforcers are isomorphic with the reduction in delay to reward correlated with terminal link stimuli. 相似文献
7.
Pigeons pecked keys on concurrent-chains schedules that provided a variable interval 30-sec schedule in the initial link.
One terminal link provided reinforcers in a fixed manner; the other provided reinforcers in a variable manner with the same
arithmetic mean as the fixed alternative. In Experiment 1, the terminal links provided fixed and variable interval schedules.
In Experiment 2, the terminal links provided reinforcers after a fixed or a variable delay following the response that produced
them. In Experiment 3, the terminal links provided reinforcers that were fixed or variable in size. Rate of reinforcement
was varied by changing the scheduled interreinforcer interval in the terminal link from 5 to 225 sec. The subjects usually
preferred the variable option in Experiments 1 and 2 but differed in preference in Experiment 3. The preference for variability
was usually stronger for lower (longer terminal links) than for higher (shorter terminal links) rates of reinforcement. Preference
did not change systematically with time in the session. Some aspects of these results are inconsistent with explanations for
the preference for variability in terms of scaling factors, scalar expectancy theory, risk-sensitive models of optimal foraging
theory, and habituation to the reinforcer. Initial-link response rates also changed within sessions when the schedules provided
high, but not low, rates of reinforcement. Within-session changes in responding were similar for the two initial links. These
similarities imply that habituation to the reinforcer is represented differently in theories of choice than are other variables
related to reinforcement. 相似文献
8.
Pigeons were given successive discrimination training in which pecking during a choice period when the key was white was either reinforced or not, depending upon the prior presence or absence of a discriminative stimulus, which was a two-element serial compound. The compound consisted of a keylight and food, with food presented second or first in a forward or backward pairing for different groups of pigeons. In Experiment 1, the sequence was an S+ indicating reinforced trials, while in Experiment 2, the sequence was an S? indicating nonreinforced trials. Following acquisition of discriminated operant behavior, a sequence generalization test was administered during which all possible orders of the two stimuli were presented on test trials prior to the onset of the choice period. The results showed that food overshadowed stimulus control by the color of the light on the key on the sequence-generalization test, independently of whether food was presented first or second during training and independently of whether food was associated with reinforcement or nonreinforcement. The similarity of results for the two experiments suggests that overshadowing occurs independently of whether the compound is a discriminative stimulus for reinforcement or nonreinforcement. Simultaneous presentation of elements of a compound stimulus is not necessary for overshadowing because the phenomenon was captured with sequentially presented stimuli. 相似文献
9.
Rats were trained in a standard 12-arm radial maze task. Following training, each trial consisted of a sequence of 2, 4, 6, 8, or 10 choices, followed by a 15-min delay, which then was followed by a choice between a single arm and a response manipulandum mounted in the center of the maze. An arm visit was reinforced if the arm had not been visited prior to the delay, whereas a manipulandum response was reinforced if the arm had been visited. It was found that rats are relatively more likely to reject arms by responding to the manipulandum following a delay occurring late in the choice sequence. This indicates that the choice criterion used by rats in the radial maze becomes more strict as the choice sequence progresses. Such a process provides an alternative explanation for some of the data recently reported by Cook, Brown, and Riley (1985). 相似文献
10.
Henry Tobin A. W. Logue John J. Chelonis Kimberly T. Ackerman Jack G. May 《Learning & behavior》1996,24(2):168-174
Two experiments tested two cynomolgus monkeys’ self-control—choice of a longer, more delayed reinforcer over a shorter, less delayed reinforcer. In Experiment 1, subjects exhibited significant selfcontrol in a procedure in which reinforcer amounts and delays were held constant throughout a condition. In Experiment 2, subjects exhibited significantly greater sensitivity to variation in reinforcer amount than to variation in reinforcer delay in a procedure in which the reinforcer delay associated with the self-control alternative was adjusted until each macaque was indifferent between the two alternatives. Both experiments indicated that, in laboratory paradigms in which humans show self-control and pigeons and rats show impulsiveness, macaques show self-control. These results are inconsistent with the hypothesis that species differences in self-control are a function of language ability or of specific types of prior training. The results are consistent with the hypothesis that species differences in self-control are related to the ratio of brain size to body weight (a possible indicator of general cognitive ability) or to shared phylogeny. 相似文献
11.
Pecking at the food key was recorded for 4 pigeons given restricted access to food. The access period was set at a fixed time in a light-dark cycle, continuous dark, or continuous light. The pecking activity occurred a few hours before onset of the access period in all three conditions. When the bird was again given free access to food after being released from restricted access, its pecking rhythm free-ran in the continuous dark. The initial phase of the rhythm coincided with the onset of the food-anticipatory pecking in the previous condition. These results suggest that the bird anticipated food access, based on its biological clock mechanism. When the access period was set in the dark phase of the light-dark cycle, anticipatory pecking did not occur, although pecking actually occurred during the access period. The pigeon’s activity is reduced during the dark phase of the light-dark cycle. Therefore, the bird’s activity level was probably too low to shape the anticipatory response, even if the access period was stored in memory in the biological clock. 相似文献
12.
Pigeons were allowed to observe a stimulus signaling food (S+) by pecking one side key of a three-key chamber, or a stimulus signaling extinction (S?) by pecking the opposite side key. Components were 30 sec long and separated by 3-sec blackouts (after extinction periods) or 3-sec access to an illuminated food hopper (terminating food periods). Pigeons came to peck the S+ key almost exclusively. When food and extinction periods were presented in random order, the S+ key was pecked in nearly every component. But when the components alternated in abab fashion, the probability of an S+ keypeck during extinction decreased (after 3-sec access to food) while remaining high in food components (after 3-sec blackout). This suggested the development of trace stimulus control by the stimuli separating the components and that redundant stimuli would maintain observing when they signaled food. Results were discussed in terms of traditional notions of conditioned reinforcement and were not seen as supporting information theory explanations of observing behavior. 相似文献
13.
Delay between choice and receipt of reinforcement (prereinforcer delay) and delay between receipt of reinforcement and the next opportunity to choose (postreinforcer delay) were varied in a discretetrials choice paradigm using four pigeons. The pigeons consistently chose the reinforcer with the smaller prereinforcer delay. Variations in postreinforcer delay did not affect choice unless prereinforcer delays were equal. The results support previous findings that prereinforcer delays contribute disproportionately to the effects of rate of reinforcer access on choice in pigeons. 相似文献
14.
Task difficulty in delayed matching-to-sample tasks (DMTS) is increased by increasing the length of a retention interval.
When tasks become more difficult, choice behavior becomes more susceptible to bias produced by unequal reinforcer ratios.
Delaying reinforcement from choice behavior also increases both task difficulty and the biasing effect of unequal reinforcer
probability. Six pigeons completed nine DMTS conditions with retention intervals of 0, 2, 4, 6, and 8 sec, in which reinforcer
delays of 0, 2, and 4 sec were combined with ratios of reinforcer probabilities of .5/.5, .2/.8, and .8/.2 for correct red
and green responses. Discriminability (logd) decreased with both increasing retention interval duration and increasing reinforcer delay. Sensitivity to reinforcement,
the tendency for ratios of choice responses to follow unequal reinforcer probabilities, also increased as a function of both
increasing retention interval and increasing reinforcer delay. The result is consistent with the view that remembering in
DMTS tasks is a discriminated operant in which increasing task difficulty increases sensitivity to reinforcement. 相似文献
15.
In Experiment 1, three food-deprived pigeons received trials that began with red or green illumination of the center pecking key. Two or four pecks on this sample key turned it off and initiated a 0- to 10-sec delay. Following the delay, the two outer comparison keys were illuminated, one with red and one with green light. In one condition, a single peck on either of these keys turned the other key off and produced either grain reinforcement (if the comparison that was pecked matched the preceding sample) or the intertrial interval (if it did not match). In other conditions, 3 or 15 additional pecks were required to produce reinforcement or the intertrial interval. The frequency of pecking the matching comparison stimulus (matching accuracy) decreased as the delay increased, increased as the sample ratio was increased, and decreased as the comparison ratio was increased. The results of Experiment 2 suggested that higher comparison ratios adversely affect matching accuracy primarily by delaying reinforcement for choosing the correct comparison. The results of Experiment 3, in which delay of reinforcement for choosing the matching comparison was manipulated, confirmed that delayed reinforcement decreases matching accuracy. 相似文献
16.
When the response of pigeons is maintained to a number of stimulus wavelengths, but extinguished to one (S?), the birds peck more rapidly at stimuli near the S? than at more distant stimuli. The present study explores this “dimensional contrast” effect as a function of the number and spacing of test wavelengths. A fixed portion of the wavelength continuum was spanned by 5, 9, 13, or 49 stimuli, which appeared in random sequence behind a standard pecking key. At the end of each 20-sec trial, pecks to test stimuli produced a conditioned reinforcer (sometimes followed by food), while pecks to the S? stimulus produced only darkness. Dimensional contrast “shoulders” developed to test stimuli on either side of the S?; these shoulders were of approximately the same height and wavelength position for all but the 5-stimulus (widely spaced) condition, and were comparable to the original contrast results with 25 stimuli. The results strongly suggest that the extent and locus of contrast shoulders are largely independent of the number and spacing of test stimuli. 相似文献
17.
In two experiments, behavioral stereotypies elicited by scheduled presentations of food and water were compared. In Experiment 1, pigeons were exposed to a fixed-time 30-sec (FT 30-sec) schedule of food or water deliveries with a brightening keylight stimulus signaling time to the unconditioned stimulus (UCS) on each trial. Food and water presentations both produced terminal autoshaped keypecking that was similarly distributed in the trial but differed in response topography and persistence. Locomotor interim behavior was different in the two motivational conditions: With food presentations, it consisted of a “retreat” to the rear of the chamber after UCS termination, followed by “pacing” in the midportion of trials. The water schedule produced very little locomotor activity with no regular distribution in the trial. Experiment 2, using a random-time 30-sec (RT 30-sec) schedule, showed that the differences in interim locomotor behavior persisted in the absence of temporal predictability of the UCS and the keypecking terminal response. The results are taken to support Timberlake’s (1983a) behavior-system theory. 相似文献
18.
This study presents a theory by which to understand how pigeons learn response patterns in simple choice situations. The theory assumes that, in a choice situation, patterns of responses compete for the final common path; that the competition is governed by two variables, the overall reinforcement probability obtained by emitting the patterns,T, and the differences in reinforcement probabilities among the patterns,D; and that the ratioD/T determines the final strength of specific response patterns. To test these predictions, three experiments were run in which pigeons were more likely to receive food when they pecked the momentarily least-preferred of three response keys. On the basis of previous research, it was predicted that the birds would be indifferent among the keys (molar aspect) and would also acquire a response pattern that consisted of pecking each key once during three consecutive trials (molecular aspect). The present theory went further and predicted that the strength of that pattern would increase with the ratioD/T. In the first two experiments,D was manipulated whileT remained constant, and in the third,T was manipulated whileD remained constant. The results agreed with the theory, for the strength of the response pattern increased withD and decreased withT, whereas overall choice proportions were always close to the matching equilibrium. 相似文献
19.
A symbolic delayed matching procedure may be used to study memory for stimulus duration in pigeons. Short and long presentations of a light sample stimulus are mapped onto the choke of visually differentiated comparison keys. When delay is varied in such a symbolic delayed matching procedure, pigeons show increasing preference for the short-sample key as the delay becomes longer (choose-short effect), even after a long sample stimulus has been presented. Two theoretical explanations of the choose-short effect are suggested. A subjective shortening model holds that the choose-short effect arises from progressive shortening of the memory of stimulus duration as the delay proceeds. An alternative coding model suggests that the choose-short effect arises from stimulus generalization after an initial response instruction to peck the long-sample key has been forgotten. These two models were tested by training pigeons to peck a third comparison key after no sample stimulus had been presented. Shifts in key preferences over delays ranging from 0 to 21 sec clearly supported the coding model. 相似文献
20.
Manipulating experience with the reinforcer, through either home cage presentations of Noyes pellets or availability of the free reinforcer immediately prior to testing, attenuated the preference for earned as opposed to free reinforcers. Similarly, changing the reinforcer to one of a different flavor at testing increased the preference for the noncontingent reinforcer. These results are consistent with an interpretation of earned reinforcer preference which emphasizes the role of the reinforcer as a discriminative signal for further instrumental responding. It is suggested that the tendency to perform instrumental responses for reinforcers when free reinforcers are available can be explained in terms of traditional learning processes. 相似文献