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When the availability of reinforcers depends on time since an event, time functions as a discriminative stimulus. Behavioral control by elapsed time is generally weak, but may be enhanced by added stimuli that act as additional time markers. The present paper assessed the effect of brief and continuous added stimuli on control by time-based changes in the reinforcer differential, using a procedure in which the local reinforcer ratio reversed at a fixed time after the most recent reinforcer delivery. Local choice was enhanced by the presentation of the brief stimuli, even when the stimulus change signalled only elapsed time, but not the local reinforcer ratio. The effect of the brief stimulus presentations on choice decreased as a function of time since the most recent stimulus change. We compared the ability of several versions of a model of local choice to describe these data. The data were best described by a model which assumed that error in discriminating the local reinforcer ratio arose from imprecise discrimination of reinforcers in both time and space, suggesting that timing behavior is controlled not only by discrimination elapsed time, but by discrimination of the reinforcer differential in time. [ABSTRACT FROM AUTHOR]

Six pigeons worked on concurrent exponential variable-interval schedules in which the relative frequency of food deliveries for responding on the two alternatives reversed at a fixed time after each food delivery. Across conditions, the point of food-ratio reversal was varied from 10 s to 30 s, and the overall reinforcer rate was varied from 1.33 to 4 per minute. The effect of rate of food delivery and food-ratio-reversal time on choice and response rates was small. In all conditions, postfood choice was toward the locally richer key, regardless of the last-food location. Unlike the local food ratio which changed in a stepwise fashion, local choice changed according to a decelerating monotonic function, becoming substantially less extreme than the local food ratio soon after food delivery. This deviation in choice appeared to result from the birds' inaccurate discrimination of the time of food deliveries; local choice was described well by a model that assumed that log response ratios matched food ratios that were redistributed across surrounding time bins with mean time t and a constant coefficient of variation. We suggest that local choice is controlled by the likely availability of food in time, and that choice matches the discriminated log of the ratio of food rates across time since the last food delivery. [ABSTRACT FROM AUTHOR]

Four pigeons were trained on two-key concurrent variable-interval schedules with no changeover delay. In Phase 1, relative reinforcers on the two alternatives were varied over five conditions from .1 to .9. In Phases 2 and 3, we instituted a molar feedback function between relative choice in an interreinforcer interval and the probability of reinforcers on the two keys ending the next interreinforcer interval. The feedback function was linear, and was negatively sloped so that more extreme choice in an interreinforcer interval made it more likely that a reinforcer would be available on the other key at the end of the next interval. The slope of the feedback function was 21 in Phase 2 and 23 in Phase 3. We varied relative reinforcers in each of these phases by changing the intercept of the feedback function. Little effect of the feedback functions was discernible at the local (interreinforcer interval) level, but choice measured at an extended level across sessions was strongly and significantly decreased by increasing the negative slope of the feedback function. [ABSTRACT FROM AUTHOR]

Abstract: Six pigeons responded on a four-key concurrent variable-interval schedule in which a 27:9:3:1 distribution of reinforcers between the keys changed every 10 reinforcers. Their behaviour quickly came under the control of this changing four-way reinforcer ratio. However, preference between a pair of keys depended not only on the relative reinforcer rates on those keys, but also on the absolute levels of those rates. This contradicts the constant-ratio rule that underpins the matching approach to choice, but is predicted by a contingency-discriminability model that assumes that organisms may occasionally misattribute reinforcers to a response that did not produce them. Reinforcers produced strong preference pulses, or transient increases in responding on the just-reinforced key. Despite accurate tracking of the reinforcer ratio, reinforcers obtained late in components and from leaner keys still produced strong pulses, suggesting both extended and local control of behaviour. Patterns of switching between keys were graded and similarly controlled by the reinforcer rates on each key. Whether considered in terms of switching, local preference pulses, or extended preference, behaviour was controlled by a rapidly changing four-way reinforcer ratio in a graduated, continuous manner that is unlikely to be explained by a simple heuristic such as fix-and-sample. [Copyright &y& Elsevier]

Abstract: Using data from two conditions of an experiment that arranged response-contingent foods and red keylight illuminations, we compared time-indexed and response-indexed preference pulses. The interpretation of red keylight effects (relative to food effects) differed according to whether time or behaviour was used to index choice in the post-event period: preference after a red keylight was more extreme than after a food in the response pulses while preference after a food was more extreme than after a keylight in the time pulses. This was due to different response latencies following the two events in combination with a tendency for initial preference to decrease as latency increased: responding began sooner after non-foods and responding that began later, after any event, tended towards indifference. Our finding suggests that preference pulses ought to be indexed according to time since the last event delivery, particularly if the response-contingent events may result in systematically different response latencies. [Copyright &y& Elsevier]

Six pigeons responded on pairs of concurrent variable-interval schedules with, in different parts, four different arrangements of alternation between schedules. Following a single switching-key response, alternation was either strict or random, and the alternative presented after a switch (the postswitch alternative) was either signaled by the location of the switching key or unsignaled. Generalized-matching analyses showed little difference in behavior among the different alternation arrangements, except the usual finding of lower sensitivity of response allocation than time allocation was eliminated by arranging random alternation. Patterns of interchangeover times were similar for all arrangements except signaled random alternation. Differences in behavior preceding the different postswitch alternatives were found in the signaled random alternation procedure. Preference was biased towards the color of the signaled postswitch alternative and showed increased sensitivity when the postswitch alternative was to be the one with the higher reinforcer rate. Interchangeover times were substantially shorter when the postswitch alternative was signaled to be different from the current alternative than when it was signaled to be the same. However, when separate reinforcer ratios were calculated for the different postswitch alternatives, those effects were eliminated or greatly reduced. We suggest that, although behavior is indeed influenced by the postswitch alternative, the mechanism is indirect. That is, the distributions of reinforcers between alternatives obtained before each postswitch alternative differ when those alternatives are signaled, and those distributions are discriminated, but the same relations between choice and relative reinforcement hold irrespective of which postswitch alternative is signaled. [ABSTRACT FROM AUTHOR]

Presents a study in which six pigeons were trained on their choice of concurrent variable-interval schedules in which two different travel times between alternatives, 4.5 and 0.5 seconds, were randomly arranged. Finding that dwell times on the alternatives were consistently longer in the presence of the stimulus that signaled the shorter travel time.

Examines the effects of overall reinforcer rate and temporal distribution of reinforcers on concurrent choices of pigeons. Experimental procedure and conditions; Response and time allocation; Sensitivity of bird to reinforcer.

Discusses the results of a study on the effects of food deprivation and session duration in pigeons. Response to food reinforcement on multiple variable-interval schedules in which the total consumption of food was entirely determined by the pigeons' interaction with the schedules.

Abstract: Five pigeons were trained in a procedure in which, with a specified probability, food was either available on a fixed-interval schedule on the left key, or on a variable-interval schedule on the right key. In Phase 1, we arranged, with a probability of 0.5, either a left-key fixed-interval schedule or a right-key variable-interval 30s, and varied the value of the fixed-interval schedule from 5s to 50s across 5 conditions. In Phase 2, we arranged either a left-key fixed-interval 20-s schedule or a right-key variable-interval 30-s schedule, and varied the probability of the fixed-interval schedule from 0.05 to 1.0 across 8 conditions. Phase 3 always arranged a fixed-interval schedule on the left key, and its value was varied over the same range as in Phase 1. In Phase 1, overall preference was generally toward the variable-interval schedule, preference following reinforcers was initially toward the variable-interval schedule, and maximum preference for the fixed-interval schedule generally occurred close to the arranged fixed-interval time, becoming relatively constant thereafter. In Phase 2, overall left-key preference followed the probability of the fixed-interval schedule, and maximum fixed-interval choice again occurred close to the fixed-interval time, except when the fixed-interval probability was 0.1 or less. The pattern of choice following reinforcers was similar to that in Phase 1, but the peak fixed-interval choice became more peaked with higher probabilities of the fixed interval. Phase 3 produced typical fixed-interval schedule responding. The results are discussed in terms of reinforcement effects, timing in the context of alternative reinforcers, and generalized matching. These results can be described by a quantitative model in which reinforcer rates obtained at times since the last reinforcer are distributed across time according to a Gaussian distribution with constant coefficient of variation before the fixed-interval schedule time, changing to extended choice controlled by extended reinforcer ratios beyond the fixed-interval time. The same model provides a good description of response rates on single fixed-interval schedules. This article is part of a Special Issue entitled: SQAB 2012. [Copyright &y& Elsevier]