bluuebunny/crossref_metadata_2025 huggingface dataset:
TEMPORAL CONTROL IN FIXED‐INTERVAL SCHEDULES
Authors: Zeiler Michael D. , Powell David G.
Published: March 2006

The peak procedure was used to study temporal control in pigeons exposed to seven fixed‐interval schedules ranging from 7.5 to 480 s. The focus was on behavior in individual intervals. Quantitative properties of temporal control depended on whether the aspect of behavior considered was initial pause duration, the point of maximum acceleration in responding, the point of maximum deceleration, the point at which responding stopped, or several different statistical derivations of a point of maximum responding. Each aspect produced different conclusions about the nature of temporal control, and none conformed to what was known previously about the way ongoing responding was controlled by time under conditions of differential reinforcement. Existing theory does not explain why Weber's law so rarely fit the results or why each type of behavior seemed unique. These data fit with others suggesting that principles of temporal control may depend on the role played by the particular aspect of behavior in particular situations.
A CONTEXTUAL MODEL OF CONCURRENT‐CHAINS CHOICE
Authors: Grace Randolph C.
Published: March 2006

An extension of the generalized matching law incorporating context effects on terminal‐link sensitivity is proposed as a quantitative model of behavior under concurrent chains. The contextual choice model makes many of the same qualitative predictions as the delay‐reduction hypothesis, and assumes that the crucial contextual variable in concurrent chains is the ratio of average times spent, per reinforcement, in the terminal and initial links; this ratio controls differential effectiveness of terminal‐link stimuli as conditioned reinforcers. Ninety‐two concurrent‐chains data sets from 19 published studies were fitted to the model. Averaged across all studies, the model accounted for 90% of the variance in pigeons' relative initial‐link responding. The model therefore demonstrates that a matching law analysis of concurrent chains—the assumption that relative initial‐link responding equals relative terminal‐link value—remains quantitatively viable. Because the model reduces to the generalized matching law when terminal‐link duration is zero, it provides a quantitative integration of concurrent schedules and concurrent chains.
THE PUZZLE OF RESPONDING MAINTAINED BY RESPONSE‐CONTINGENT SHOCK
Authors: Laurence Michael T. , Hineline Philip N. , Bersh Philip J.
Published: March 2006

Four squirrel monkeys were first exposed to a sequence of procedures that reliably generate responding maintained by brief response‐contingent electric shocks arranged according to a fixed‐interval schedule. After responding had become stable on the fixed‐interval schedule, additional contingencies were added in tandem, whereby after completion of the interval, the spacing of responses affected shock delivery. In one procedure, responses had to be spaced more widely than their previous median value if shock were to be delivered. In the other procedure, responses had to be spaced more closely to produce shock. On the first of these procedures, decreased but stable response rates would indicate that shock functioned as a positive reinforcer; on the second, increased response rates would indicate the positively reinforcing function. Instead, response rates accelerated on the procedure that targeted more widely spaced responses for shock delivery, and decelerated or ceased on the procedure that arranged for shocks to be produced by more closely spaced responses. Consistent with other recent findings, these results question the interpretation of performances maintained by response‐contingent shock as engendered by positive reinforcement and are consistent with aversive‐control interpretations. The details of that aversive control are not entirely clear, however, and these same procedures would be informative if applied to shock‐maintained behavior that is generated in other ways.
IN VITRO REINFORCEMENT OF HIPPOCAMPAL BURSTING: A SEARCH FOR SKINNER'S ATOMS OF BEHAVIOR
Authors: Stein Larry , Xue Bao G. , Belluzzi James D.
Published: March 2006

A novel “in vitro reinforcement” paradigm was used to investigate Skinner's (1953) hypotheses (a) that operant behavior is made up of infinitesimal “response elements” or “behavioral atoms” and (b) that these very small units, and not whole responses, are the functional units of reinforcement. Our tests are based on the assumption that behavioral atoms may plausibly be represented at the neural level by individual cellular responses. As a first approach, we attempted to reinforce the bursting responses of hippocampal units in a highly reduced brain‐slice preparation with local micropressure applications of behaviorally reinforcing dopaminergic drugs. The same injections were administered independently of bursting to provide a “noncontingent” control for nonspecific stimulation or facilitation of firing. It was found that the bursting responses of individual CA1 pyramidal neurons may be progressively facilitated in a dose‐related manner by response‐contingent (but not noncontingent) injections of dopamine itself, the dopamine D1‐preferring agonist SKF 82958, the D3‐preferring agonist quinpirole, and the D2‐like selective agonist (+)‐4‐propyl‐9 hydroxynapthoxazine. These findings support the conclusion that unit bursting responses can be reinforced in vitro in hippocampal slices, and they further suggest that the same dopamine receptor subtypes are involved in both cellular and behavioral operant conditioning. The results thus provide indirect support for Skinner's atoms‐of‐behavior hypothesis.
INCREASING AND SIGNALING BACKGROUND REINFORCEMENT: EFFECT ON THE FOREGROUND RESPONSE—REINFORCER RELATION
Authors: Belke Terry W. , Heyman Gene M.
Published: March 2006

Herrnstein's (1970) hyperbolic matching equation describes the relationship between response rate and reinforcement rate. It has two estimated parameters, k and Re. According to one interpretation, k measures motor performance and Re measures the efficacy of the reinforcer maintaining responding relative to background sources of reinforcement. Experiment 1 tested this interpretation of the Re parameter by observing the effect of adding and removing an additional source of reinforcement to the context. Using a within‐session procedure, estimates of Re were obtained from the response—reinforcer relation over a series of seven variable‐interval schedules. A second, concurrently available variable‐interval schedule of reinforcement was added and then removed from the context. Results showed that when the alternative was added to the context, the value of Re increased by 107 reinforcers per hour; this approximated the 91 reinforcers per hour obtained from this schedule. Experiment 2 investigated the effects of signaling background reinforcement on k and Re. The signal decreased Re, but did not have a systematic effect on k. In general, the results supported Herrnstein's interpretation that in settings with one experimenter‐controlled reinforcement source, Re indexes the strength of the reinforcer maintaining responding relative to uncontrolled background sources of reinforcement.
EFFECTS OF QUALITATIVELY DIFFERENT REINFORCERS ON THE PARAMETERS OF THE RESPONSE‐STRENGTH EQUATION
Authors: Petry Nancy M. , Heyman Gene M.
Published: March 2006

This experiment examined the relationship between two qualitatively different reinforcers and the parameters of a quantitative model of reinforced responding, referred to as the response‐strength equation or the Herrnstein equation. A group of rats was first food deprived and later water deprived. An 11.5% sucrose solution served as the reinforcer in the food‐deprivation condition, and water was the reinforcer in the water‐deprivation condition. Each experimental session consisted of a series of seven variable‐interval schedules, providing reinforcement rates that varied between 20 and 1,200 reinforcers per hour. The response rates increased in a negatively accelerating function in a manner consistent with the response‐strength equation. This equation has two fitted parameters, k and Re. According to one theory, the k parameter is a measure of motor performance, and Re is indicative of the relative reinforcement efficacy of the background uncontrollable sources of reinforcement in relation to the experimentally arranged reinforcer. In this study, k did not change as a result of the different reinforcers, but Re was significantly larger in the sucrose‐reinforcement condition. These results are consistent with the interpretation that k and Re measure two independent and experimentally distinguishable parameters and provide further evidence that absolute response rate is a function of relative reinforcement rate, as implied by the derivation of the response‐strength equation based on the matching law.
SOCIAL REINFORCEMENT OF OPERANT BEHAVIOR IN RATS: A METHODOLOGICAL NOTE
Authors: Evans Mycroft J. , Duvel Adam , Funk Michele L. , Lehman Brooke , Sparrow John , Watson Nathan T. , Neuringer Allen
Published: March 2006

An apparatus was developed to study social reinforcement in the rat. Four Long‐Evans female rats were trained to press a lever via shaping, with the reinforcer being access to a castrated male rat. Responding under a fixed‐ratio schedule and in extinction was also observed. Social access was found to be an effective reinforcer. When social reinforcement was compared with food reinforcement under similar conditions of deprivation and reinforcer duration, no significant differences were observed.
PREDICTING AND SCALING HENS' PREFERENCES FOR TOPOGRAPHICALLY DIFFERENT RESPONSES
Authors: Sumpter Catherine E. , Foster T. Mary , Temple William
Published: March 2006

Six hens were exposed to several concurrent (second‐order) variable‐interval schedules in which the response requirements on the alternatives were varied. The response requirements were one key peck versus five key pecks, one key peck versus one door push, and five key pecks versus one door push. Response‐ and time‐allocation ratios undermatched the obtained reinforcement ratios but were well described by the generalized matching law. Time and response bias estimates from two pairs of response requirements were used to predict bias in the third pairing. The predicted values were close to those obtained; this result supports the notion that both numerically and topographically different responses act as constant sources of bias within the generalized matching law. The differences between the response and time biases could be accounted for by the different times needed to complete each response requirement. The results also suggest that the door push is a useful operant for research with domestic hens.
THE EFFECTS OF COCAINE ON BEHAVIOR MAINTAINED BY TIMEOUT FROM AVOIDANCE
Authors: Galizio Mark , Liborio Margaret O.
Published: March 2006

Rats were trained on concurrent schedules under which responses on one lever postponed shock (avoidance) and responses on the other lever produced brief (2‐min) periods of signaled timeout from avoidance. For 6 rats, timeout from avoidance was programmed on a variable‐interval 45‐s schedule that generally resulted in rates that were lower than those on the avoidance lever. For another 6 rats, timeout was arranged on a variable‐ratio 15 schedule that produced higher baseline rates. Cocaine (3 to 40 mg/kg) produced large, dose‐dependent increases in behavior maintained by timeout in both groups of rats. Avoidance responding was also generally increased by cocaine, but the increases were of lesser magnitude. Increases in response rates were seen across a broad range of doses on behavior maintained by either interval or ratio schedules, an outcome that was unexpected on the basis of most studies of cocaine on food‐maintained behavior. These results were similar to those of previous studies of the effects of amphetamine on behavior maintained by timeout from avoidance and suggest that stimulant drugs affect behavior maintained under a shock‐postponement schedule differently than they affect behavior maintained by timeout from avoidance.
CONTRAST AND REALLOCATION OF EXTRANEOUS REINFORCERS AS A FUNCTION OF COMPONENT DURATION AND BASELINE RATE OF REINFORCEMENT
Authors: McLean Anthony P.
Published: March 2006

Four pigeons responded on multiple schedules arranged on a “main” key in a two‐key experimental chamber. A constant schedule component was alternated with another component that was varied over conditions. On an extra response key, conjoint schedules of reinforcement that operated in both components were arranged concurrently with the multiple schedule on the main key. On the main key, changes in reinforcement rate in the varied component were inversely related to changes in response rates in the constant component (behavioral contrast). On the extra key, some reinforcers were reallocated between components, depending on the schedules in effect on the main key in the varied component. In the varied component, the obtained rates of reinforcement on the extra key were inversely related to main‐key reinforcement rate. In the constant component, extra‐key reinforcer rates were positively related to main‐key reinforcer rates obtained in the varied component, and were not a function of response rates on the extra key. In two comparisons, the rate at which components alternated and the value of the main‐key schedule in the constant component were varied. Consistent with earlier work, long components reduced the extent of contrast. Reductions in contrast as a function of component duration were accompanied by similar reductions in the extent of reinforcer reallocation on the extra key. In the second comparison, lowering the rate of reinforcement in the constant component increased the rate at which extra‐key reinforcers were obtained, reduced the extent of reinforcer reallocation, and reduced contrast. Overall, the results are consistent with the suggestion that some contrast effects are due to the changes in extraneous reinforcement during the constant component, and that manipulations of component duration, and manipulations of the rate of reinforcement in the constant component, affect contrast because they influence the extent of extraneous reinforcer reallocation.
DELAYED MATCHING‐TO‐SAMPLE PERFORMANCE: EFFECTS OF RELATIVE REINFORCER FREQUENCY AND OF SIGNALED VERSUS UNSIGNALED REINFORCER MAGNITUDES
Authors: McCarthy Dianne , Voss Philip
Published: March 2006

Six pigeons were trained on a delayed red‐green matching‐to‐sample task that arranged four delays within sessions. Matching responses intermittently produced either 1.5‐s access to food or 4.5‐s access to food, and nonmatching responses produced either 1.5‐s or 4.5‐s blackout. Two phases were conducted: a signaled phase in which the reinforcer magnitudes (small and large) were signaled by houselights (positioned either on the left or right of the chamber), and an unsignaled phase in which there was no correlation between reinforcer magnitude and houselight position. In both phases, the relative frequency with which red and green matching responses produced food was varied across five values. Both matching accuracy and the sensitivity of performance to the distribution of reinforcers for matching responses decreased with increasing delays in both phases. In addition, accuracy and reinforcer sensitivity were significantly lower on signaled small‐reinforcer trials compared with accuracy and sensitivity values on signaled large‐reinforcer trials and on both types of unsignaled trials. These results are discussed in the context of research on both nonhuman animal and human memory.
EFFECTS OF A VARIABLE‐RATIO CONDITIONING HISTORY ON SENSITIVITY TO FIXED‐INTERVAL CONTINGENCIES IN RATS
Authors: Baron Alan , Leinenweber Antoinette
Published: March 2006

We investigated the possibility that human‐like fixed‐interval performances would appear in rats given a variable‐ratio history (Wanchisen, Tatham, & Mooney, 1989). Nine rats were trained under single or compound variable‐ratio schedules and then under a fixed‐interval 30‐s schedule. The histories produced high fixed‐interval rates that declined slowly over 90 sessions; differences as a function of the particular history were absent. Nine control animals given only fixed‐interval training responded at lower levels initially, but rates increased with training. Despite differences in absolute rates, rates within the intervals and postreinforcement pauses indicated equivalent development of the accelerated response patterns suggestive of sensitivity to fixed‐interval contingencies. The finding that the histories elevated rates without retarding development of differentiated patterns suggests that the effective response unit was a burst of several lever presses and that the fixed‐interval contingencies acted on these units in the same way as for single responses. Regardless of history, the rats did not manifest the persistent, undifferentiated responding reported for humans under comparable schedules. We concluded that the shortcomings of animal models of human fixed‐interval performances cannot be easily remedied by including a variable‐ratio conditioning history within the model.
CHOICE AS A FUNCTION OF REINFORCEMENT RATIOS IN DELAYED MATCHING TO SAMPLE
Authors: Hartl Josef A. , Fantino Edmund
Published: March 2006

Pigeons were studied in two experiments using a delayed matching‐to‐sample task. In Experiment 1, 4 subjects were exposed to a task in which the proportion of reinforcement associated with matching and nonmatching, and the overall proportion of reinforcement associated with selecting each choice, regardless of the sample stimulus, were varied. Choice was sensitive to both proportions. A least squares regression analysis showed that Wixted's (1989) proportions of reinforcement model closely fit the data from Experiment 1; however, the model failed to make accurate qualitative predictions for some test conditions. In Experiment 2, 4 subjects were exposed to a delayed matching‐to‐sample task in which the retention intervals and the reduction in delay to reinforcement signaled by the onset of the sample stimulus were independently varied. When the retention interval was short and when the delay‐reduction value of the sample stimulus was high, the sample exerted greater control over choice; the control by the overall proportion of reinforcements for selecting each choice stimulus was correspondingly low. Conversely, when the retention interval was long and the delay‐reduction value of the sample stimulus was low, the sample exerted relatively less control over choice; control by the overall proportion of reinforcements obtained for selecting each choice stimulus was correspondingly high. A signal detection analysis found that sensitivity to reinforcement varied directly with retention interval. Data were also consistent with misallocation models. No evidence was found to suggest that pigeons ignore the rate at which selecting individual choice stimuli is reinforced, as has been reported in studies with human subjects.
DYNAMICS OF TIME DISCRIMINATION: II. THE EFFECTS OF MULTIPLE IMPULSES
Authors: Higa Jennifer J.
Published: March 2006

According to a diffusion generalization model, time discrimination is determined by the frequency and recency of preceding intervals of time. A procedure for studying rapid timing was used to investigate whether pigeons' wait‐time responses were sensitive to these factors. In Experiment 1 the number (two or eight) and spacing (consecutive or far apart) of 5‐s interfood intervals (called impulses) intercalated in a series of 15‐s interfood intervals (nonimpulses) were studied. Experiment 2 was identical to the first but the interfood intervals were increased by a factor of three. Overall, impulses shortened wait times in the next interfood interval. However, several impulses occurring in succession extended the localized effect of an impulse: Wait times following a set of eight‐close impulses were slow to recover to preimpulse levels. The results show that linear waiting is only an approximation to the dynamic process, and a process that is sensitive to events in an animal's remote past, such as the diffusion generalization model, provides a better account of rapid timing effects.
INVESTIGATING BEHAVIORAL DYNAMICS WITH A FIXED‐TIME EXTINCTION SCHEDULE AND LINEAR ANALYSIS
Authors: Palya William L. , Walter Don , Kessel Robert , Lucke Robert
Published: March 2006

This paper describes the behavioral adaptation observed for 16 pigeons responding to a step transition in the reinforcement rate in a repeated‐trial design. Within each trial, following exposure for a fixed period to a variable‐interval schedule, there was an unsignaled change in the schedule to extinction. The step transition allowed an experimental test of the applicability of a linear analysis to steady‐state dynamic behavior. The computations required for this test yielded, as an intermediate result, transfer functions for each of the 16 birds from 1 mHz to 256 mHz. The transfer functions obtained show greater responsiveness to lower frequencies (i.e., longer time‐scale structures in the reinforcement schedule); hence, the pigeons have the characteristics of a low‐pass filter. The outcome of the test is that some predictability of the pigeons' future behavior is possible.
KEY‐PECK PROBABILITY AND TOPOGRAPHY IN A CONCURRENT VARIABLE‐INTERVAL VARIABLE‐INTERVAL SCHEDULE WITH FOOD AND WATER REINFORCERS
Authors: Ploog Bertram O. , Zeigler H. Philip
Published: March 2006

The relation between variables that modulate the probability and the topography of key pecks was examined using a concurrent variable‐interval variable‐interval schedule with food and water reinforcers. Measures of response probability (response rates, time allocation) and topography (peck duration, gape amplitude) were obtained in 5 water‐ and food‐deprived pigeons. Key color signaled reinforcer type. During baseline, response rates and time allocations were greater to the food key than to the water key, and food‐key pecks had larger gapes and shorter durations. Relative probability measures (for the food key) were increased by prewatering and decreased by prefeeding. Deprivation effects upon topography measures were apparent only when food‐ and water‐key pecks were analyzed separately. Food‐key gape amplitudes increased with prewatering and decreased with prefeeding. The clearest effect occurred with prewatering. There were no consistent effects upon water‐key gapes. The key color—reinforcer relation was reversed for 3 pigeons to determine how response topography was modulated during the transition from food‐ to water‐key pecks. Reacquisition was faster for the probability than for the topography measures. Analysis of gape‐amplitude distributions during reversal indicated that response‐form modulation proceeded through the generation of intermediate gape sizes.
THE DISCRIMINATION OF RELATIVE FREQUENCY BY PIGEONS
Authors: Machado Armando , Cevik Munire
Published: March 2006

Five experiments addressed the issue of how pigeons learn to discriminate the relative frequency of stimuli. During a sampling period, three different stimuli (keylights) were presented serially, in mixed order, and with different frequencies. During a choice period, the stimuli were presented simultaneously, and reinforcement was arranged for choosing the stimulus that was presented the least number of times during the sample. The results showed that (a) the overall proportion of correct choices was always above chance levels; (b) the likelihood of a correct choice decreased with the serial position of the correct stimulus, a negative recency effect; (c) when the last three stimuli of the sample were constrained to be one of each kind, the negative recency effect decreased but errors became more likely when the correct stimulus occurred early in the sample, a negative primacy effect; (d) accurate performance generalized to new and larger samples; and (e) under some conditions the probability of a correct choice was independent of the serial position of the correct stimulus. The serial position curves suggest that in a least frequent discrimination task, two processes determine how the least frequent stimulus controls behavior: a passive decay process (the stimulus loses its effectiveness with time since its last occurrence), and a residual salience process (when the stimulus occurs in the first position it may decay to a higher asymptote than when it occurs in later positions).
LEARNING ABOUT FOOD: STARLINGS, SKINNER BOXES, AND EARTHWORMS
Authors: Dall Sasha R. X. , Cuthill Innes C. , Cook Nikalas , Morphet Matt
Published: March 2006

Despite its importance as a tool for understanding a wide range of animal behavior, the study of reinforcement schedules in the laboratory has suffered from difficulties in the biological interpretation of its findings. This study is an operant‐laboratory investigation of the ability of European starlings, Sturnus vulgaris, to learn to respond adaptively to the problem of foraging on patchily distributed prey that are uncertainly located in space. In order to maximize the biological relevance of the laboratory study, variation in the aggregation of earthworms, Lumbricus terrestris (a prey species), was rigorously quantified from the field, and the experimental birds were presented with reinforcement schedules designed to represent the extremes of the observed variation. The results demonstrate that, even for a single prey species, the degree to which individuals are aggregated can vary markedly over a range of spatial scales, and that starlings can rapidly learn to respond, in an adaptive manner, to these variations. These findings suggest that starlings are capable of adjusting their behavior to facilitate the efficient exploitation of prey that occurs in patches of an uncertain nature, and thus illustrate the heuristic value of an ecologically informed operant‐laboratory approach to studying foraging behavior.
NONSTABLE CONCURRENT CHOICE IN PIGEONS
Authors: Schofield Grant , Davison Michael
Published: March 2006

Six pigeons were trained on concurrent variable‐interval schedules in which the arranged reinforcer ratios changed from session to session according to a 31‐step pseudorandom binary sequence. This procedure allows a quantitative analysis of the degree to which performance in an experimental session is affected by conditions in previous sessions. Two experiments were carried out. In each, the size of the reinforcer ratios arranged between the two concurrent schedules was varied between 31‐step conditions. In Experiment 1, the concurrent schedules were arranged independently, and in Experiment 2 they were arranged nonindependently. An extended form of the generalized matching law described the relative contribution of past and present events to present‐session behavior. Total performance in sessions was mostly determined by the reinforcer ratio in that session and partially by reinforcers that had been obtained in previous sessions. However, the initial exposure to the random sequence produced a lower sensitivity to current‐session reinforcers but no difference in overall sensitivity to reinforcement. There was no evidence that the size of the reinforcer ratios available on the concurrent schedules affected either overall sensitivity to reinforcement or the sensitivity to reinforcement in the current session. There was also no evidence of any different performance between independent and nonindependent scheduling. Because of these invariances, this experiment validates the use of the pseudorandom sequence for the fast determination of sensitivity to reinforcement.
THE CONTROL OF CHOICE BY ITS CONSEQUENCES
Authors: Jones B. Max , Davison Michael
Published: March 2006

Five pigeons were trained on concurrent variable‐interval schedules in which equal rates of reinforcement were always arranged for left‐ and right‐key responses, but different overall rates were signaled by key colors. Sessions began with both keys lit yellow for the instrumental phase. If, after 20 s of this phase, the relative number of responses that had been made to the left key equaled or exceeded .75, both keys changed red for the contingent phase. The contingent phase arranged another concurrent variable‐interval schedule for a further 20 s before the instrumental phase was reinstated. However, if preference in the instrumental phase did not exceed .75, the instrumental phase continued for a further 20 s before preference was again compared with the criterion. In Part 1, the reinforcer rate arranged in the instrumental phase was held constant at 4.8 reinforcers per minute, while the reinforcer rate arranged in the contingent phase was varied across conditions from 0 to 19.2 over five steps. In Part 2, reinforcer rates in the contingent phase were kept constant at 36 per minute, while reinforcer rates in the instrumental phase were varied from 0 to 36 over seven steps. Part 3 replicated Part 2 but used reinforcer rates in both phases that were one third of those arranged in Part 2. Measures of choice obtained by summing responses across presentations of the instrumental phase became more extreme toward the left key as the reinforcer rate obtained in the contingent phase was increased (Part 1) and as the reinforcer rate obtained in the instrumental phase was decreased (Parts 2 and 3). Changes in these measures of choice were accompanied by systematic changes in the relative frequency with which the criterion was exceeded. Changes in both these measures were correlated with changes in the relative frequency with which subjects responded exclusively to the left key. These results are discussed with respect to the two choices that were concurrently available in this procedure and the response alternatives that might constitute the concurrent operants in each choice.
PIGEONS' CHOICES BETWEEN FIXED‐RATIO AND GEOMETRICALLY ESCALATING SCHEDULES
Authors: Neuman Paul , Ahearn William H. , Hineline Philip N.
Published: March 2006

When pigeons choose between situations that provide access to food reinforcers after a delay, choice is better predicted by computations based upon sums‐of‐reciprocals distances from the point of choice to each of the next three or four reinforcers in series than by computations of optimality based upon mean rates of reinforcement. The present experiments were designed to examine the generality of this finding. Pigeons were exposed to concurrent‐chains schedules in which one brief initial link led to a fixed‐ratio schedule (either 15, 30, or 60, depending on the condition), and the other link led to a geometrically increasing progressive‐ratio schedule whose rate of escalation was systematically varied across conditions. Each combination of fixed‐ratio size and escalation rate of the progressive schedule was assessed at two different levels of deprivation (75% and 80% of free‐feeding weights). Computations based upon the sums‐of‐reciprocals principle, treating ratio schedule sizes as proportional to delays, predicted and described the pigeons' median switch points better than those based on arithmetic means. Neither the distance to the next reinforcer (as implied by some molecular analyses) nor molar optimization (as described by arithmetic means) were as successful at accounting for patterns of choice in these situations. Hence, it appears that the birds' choices were most influenced by the relative proximity of a choice to several reinforcers in a series of reinforcers, with each of the less proximal reinforcers having relatively less influence over the current choice.
RESPONSE‐INDEPENDENT EVENTS IN THE BEHAVIOR STREAM
Authors: Lattal Kennon A. , Abreu‐Rodrigues Josele
Published: March 2006

The metaphor of the behavior stream provides a framework for studying the effects of response‐independent food presentations intruded into an environment in which operant responding of pigeons was maintained by variable‐interval schedules. In the first two experiments, response rates were reduced when response‐independent food was intruded during the variable‐interval schedule according to a concomitantly present fixed‐time schedule. These reductions were not always an orderly function of the percentage of response‐dependent food. Negatively accelerated patterns of key pecking across the fixed‐time period occurred in Experiment 1 under the concomitant fixed‐time variable‐interval schedules. In Experiment 2, positively and negatively accelerated and linear response patterns occurred even though the schedules were similar to those used in Experiment 1. The variable findings in the first two experiments led to three subsequent experiments that were designed to further illuminate the controlling variables of the effects of intruded response‐independent events. When the fixed and variable schedules were correlated with distinct operanda by employing a concurrent fixed‐interval variable‐interval schedule (Experiment 3) or with distinct discriminative stimuli (Experiments 4 and 5), negatively accelerated response patterns were obtained. Even in these latter cases, however, the response patterns were a joint function of the physical separation of the two schedules and the ratio of fixed‐time or fixed‐interval to variable‐interval schedule food presentations. The results of the five experiments are discussed in terms of the contributions of both reinforcement variables and discriminative stimuli in determining the effects of intruding response‐independent food into a stream of operant behavior.
PROCRASTINATION BY PIGEONS WITH FIXED‐INTERVAL RESPONSE REQUIREMENTS
Authors: Mazur James E.
Published: March 2006

Two experiments studied the phenomenon of procrastination, in which pigeons chose a larger, more delayed response requirement over a smaller, more immediate response requirement. The response requirements were fixed‐interval schedules that did not lead to an immediate food reinforcer, but that interrupted a 55‐s period in which food was delivered at random times. The experiments used an adjusting‐delay procedure in which the delay to the start of one fixed‐interval requirement was varied over trials to estimate an indifference point—a delay at which the two alternatives were chosen about equally often. Experiment 1 found that as the delay to a shorter fixed‐interval requirement was increased, the adjusting delay to a longer fixed‐interval requirement also increased, and the rate of increase depended on the duration of the longer fixed‐interval requirement. Experiment 2 found a strong preference for a fixed delay of 10 s to the start of a fixed‐interval requirement compared to a mixed delay of either 0 or 20 s. The results help to distinguish among different equations that might describe the decreasing effectiveness of a response requirement with increasing delay, and they suggest that delayed reinforcers and delayed response requirements have symmetrical but opposite effects on choice.
GROUP CHOICE: COMPETITION, TRAVEL, AND THE IDEAL FREE DISTRIBUTION
Authors: Baum William M. , Kraft John R.
Published: March 2006

If a group of foragers distributes among resource patches according to the ideal free distribution, the relative number of foragers in each patch should match the relative amount of resource obtained there, unless deviations arise from factors such as incomplete information or interforager interference. In analogy to individual choice, such effects may produce undermatching—group distribution falling short of resource distribution—or overmatching—group distribution overshooting resource distribution. In the present experiments, a flock of about 30 pigeons distributed between two patches with continuous inputs of green peas. Competition was varied by changing the size or extent of the patches. When the patches were areas or troughs, some undermatching occurred. When the patches were small bowls, strong undermatching occurred. When travel was required to switch patches, undermatching decreased slightly. A visual barrier that prevented pigeons from seeing one patch from the other had no effect. Overall rate of food delivery, varied over a wide range, had no effect. It appeared that the mechanism of flock distribution depended on comparisons between patches that were successive rather than simultaneous. Although most pigeons participated in the experiments, and different pigeons participated to different extents, individual pigeons tended to be consistent in the extent of participation from session to session, suggesting the possibility that participation might reflect competitive ability. Examination of the preferences and switching of individual pigeons revealed no consistency within or across individuals. It appeared that the flock's distribution was a truly emergent phenomenon, in the sense that results at the level of the flock in no way paralleled behavior at the level of the individual.
EFFECTS OF VARYING SAMPLE‐ AND CHOICE‐STIMULUS DISPARITY ON SYMBOLIC MATCHING‐TO‐SAMPLE PERFORMANCE
Authors: Godfrey Rebecca , Davison Michael
Published: March 2006

Six pigeons were trained on a typical two‐stimulus two‐response symbolic matching‐to‐sample task involving the discrimination of sample and choice stimuli that were signaled by different probabilities that pixels in an area were lit on a computer screen located behind the response keys. The disparities of the sample and choice stimuli were systematically varied across five experimental parts by manipulating the probabilities of pixel illumination. Across conditions within parts, the ratio of reinforcers obtainable for matching responses was varied over five levels. A recent model of detection based on the discriminability between the stimulus—response relations and between response—reinforcer relations provided an effective description of the data. Consistent with this model, changes in the disparity of the sample stimuli led to decreases in stimulus—response discriminability and left response—reinforcer discriminability unchanged. Equally, changes in choice‐stimulus disparity caused a decrease in estimates of response—reinforcer discriminability and not in stimulus—response discriminability. Parameter invariance was thus obtained, and the variables expected to affect these parameters (sample and choice stimulus disparity) were correctly identified. The reasons for the failure of two recently reported studies to support parameter invariance under this model are discussed.
PERFORMANCE ON CONCURRENT VARIABLE‐INTERVAL EXTINCTION SCHEDULES
Authors: Davison Michael , Jones B. Maxwell
Published: March 2006

Six homing pigeons were trained on concurrent variable‐interval extinction schedules in a switching‐key procedure. The discriminative stimuli and associated schedules in operation were selected randomly after each switch and each reinforcer. More than 80 daily sessions were arranged in each of five experimental conditions that varied the reinforcer rate on the variable‐interval schedule. Behavior allocation remained nonexclusive even after extended training and did not change systematically as a function of the reinforcer rate. Both of these findings are predicted by a contingency‐discriminability description of choice and are incompatible with a generalized matching description.
MENTAL ROTATION AND TEMPORAL CONTINGENCIES
Authors: Cohen Dale J. , Blair Christopher
Published: March 2006

A task that requires subjects to determine whether two forms of the same shape, but in different orientations, are mirror images or identical except for orientation is called a handedness recognition task. Subjects' reaction times (RT) on this task are consistently related to the angular disparity (termed a) between the two presented forms. This pattern of data has been interpreted to indicate that subjects solve the task by imagining that one of the forms rotates into the orientation of the other (termed mental rotation). The speed with which one imagines one of the forms rotating has been widely considered a fixed capability of the individual, and thus immune to the effect of contingencies. We present an experiment that assesses the effects of temporal contingencies in a handedness recognition task on the slope of the function RT = f(α). The data indicate that the slope of this function can come under the control of temporal contingencies.
MATCHING UNDER NONINDEPENDENT VARIABLE‐RATIO SCHEDULES OF DRUG REINFORCEMENT
Authors: Meisch Richard A. , Spiga Ralph
Published: March 2006

Response‐contingent deliveries of oral pentobarbital maintained responding of 3 rhesus monkeys during daily 3‐hr sessions. Deliveries of pentobarbital were arranged under nonindependent concurrent variable‐ratio variable‐ratio schedules. Responses to either schedule counted toward completion of both variable‐ratio schedule requirements. This schedule is similar in some respects to conventional concurrent variable‐interval variable‐interval schedules, in which passage of time counts toward completion of the interval value on both schedules. Restricted nonindependent concurrent variable‐ratio variable‐ratio schedules were also studied. On that schedule, when a drug delivery was assigned to one spout, it had to be collected before responses on the opposite spout again counted toward completion of the schedule requirements. Relative reinforcer magnitude was varied by changing the drug concentration on one schedule while keeping the drug concentration constant on the other variable‐ratio schedule. Under both types of concurrent variable‐ratio variable‐ratio schedules, the relative rate of responding corresponded to the relative drug intake. Unlike earlier studies of concurrent variable‐interval variable‐interval intravenous cocaine reinforcement, preference was proportionate to concentration, and exclusive preferences did not develop. The relationship between relative rate of responding and relative drug intake was well described by the generalized matching law.
CONTROL BY SAMPLE LOCATION IN PIGEONS' MATCHING TO SAMPLE
Authors: Lionello Karen M. , Urcuioli Peter J.
Published: March 2006

Three experiments assessed the impact of sample location in pigeons' matching to sample. Experiments 1 and 2 demonstrated that after line or hue identity matching was acquired to high levels of accuracy with center‐key samples, varying sample location across the three keys disrupted performances. The drop in accuracy occurred following both zero‐delay and simultaneous training and was mostly confined to trials in which the sample appeared on a side key. Experiment 3 attempted to diminish control by location by training birds to match samples that could appear in any location prior to center‐key sample training and moving‐sample testing with another set of stimuli. In testing, all birds performed accurately on center‐sample trials and on side‐key sample trials in which the matching choice appeared on the center key. Accuracy was below chance, however, on side‐key sample trials in which the matching choice appeared on the other side key. One implication of the persistent control by sample location in the three‐key paradigm is that it precludes the possibility of symmetry because symmetry tests require a change in the locations at which samples and comparisons appear.
CONTEXT EFFECTS ON CHOICE
Authors: Goldshmidt Jay N. , Lattal K. Matthew , Fantino Edmund
Published: March 2006

Four pigeons responded on a concurrent‐chains schedule in four experiments that examined whether the effectiveness of a stimulus as a conditioned reinforcer is best described by a global approach, as measured by the average interreinforcement interval, or by a local contextual approach, as measured by the onset of the stimulus preceding the conditioned reinforcer. The interreinforcement interval was manipulated by the inclusion of an intertrial interval, which increased the overall time to reinforcement but did not change the local contingencies on a given trial. A global analysis predicted choice for the richer alternative to decrease with the inclusion of an intertrial interval, whereas a local analysis predicted no change in preference. Experiment 1 examined sensitivity to intertrial intervals when each was signaled by the same houselight that operated throughout the session. In Experiment 2, the intertrial interval always was signaled by the stimulus correlated with the richer terminal link. In Experiment 3, the intertrial interval was signaled by the keylights correlated with the initial links and two novel houselights. Experiment 4 provided free food pseudorandomly during the intertrial interval. In all experiments, subjects' preferences were consistent with a local analysis of choice in concurrent chains. These results are discussed in terms of delay‐reduction theory, which traditionally has failed to distinguish global and local contexts.
OPERANTS WERE NEVER “EMITTED,” FEELING IS DOING, AND LEARNING TAKES ONLY ONE TRIAL: A REVIEW OF B. F. SKINNER'S RECENT ISSUES IN THE ANALYSIS OF BEHAVIOR
Authors: Malone John C.
Published: March 2006

This final collection of Skinner's papers was intended for the professional, although other readers will find much of interest. The first five chapters are devoted to what Skinner called “theoretical issues” and include clear presentations of his positions on “feelings” and on the “self” as an apparent agent of volition. Skinner skillfully discusses thinking, the origins of cognitive‐mediational theories, and a favorite topic: the similarity of processes occurring in the histories of species and of individuals. The next four chapters cover what he called “professional issues,” including the often‐misunderstood philosophy known as radical behaviorism as well as the operant aspects of behavior therapy and attempts to influence educational practices. He seemed disappointed in the lack of acceptance of programmed learning methods and pessimistic about the possibility of improving education practices. This pessimism was evident in the final section, “personal issues,” in which he expressed doubt that the powerful and self‐serving forces of government, business, and religion will ever permit the changes that could be wrought by the application of behavior analysis to the great problems of society. Two other chapters in the last section will be useful to historians who are curious about the influence of logical positivism on Skinner's thinking (apparently there was not much influence) and to sophisticated readers who are interested in Skinner's retrospective consideration of his work.
DELAY OR PROBABILITY DISCOUNTING IN A MODEL OF IMPULSIVE BEHAVIOR: EFFECT OF ALCOHOL
Authors: Richards Jerry B. , Zhang Lan , Mitchell Suzanne H. , de Wit Harriet
Published: March 2006

Little is known about the acute effects of drugs of abuse on impulsivity and self‐control. In this study, impulsivity was assessed in humans using a computer task that measured delay and probability discounting. Discounting describes how much the value of a reward (or punisher) is decreased when its occurrence is either delayed or uncertain. Twenty‐four healthy adult volunteers ingested a moderate dose of ethanol (0.5 or 0.8 g/kg ethanol; n = 12 at each dose) or placebo before completing the discounting task. In the task the participants were given a series of choices between a small, immediate, certain amount of money and $10 that was either delayed (0, 2, 30, 180, or 365 days) or probabilistic (i.e., certainty of receipt was 1.0, .9, .75, .5, or .25). The point at which each individual was indifferent between the smaller immediate or certain reward and the $10 delayed or probabilistic reward was identified using an adjusting‐amount procedure. The results indicated that (a) delay and probability discounting were well described by a hyperbolic function; (b) delay and probability discounting were positively correlated within subjects; (c) delay and probability discounting were moderately correlated with personality measures of impulsivity; and (d) alcohol had no effect on discounting.