bluuebunny/crossref_metadata_2025 huggingface dataset:
EFFECTS OF VARIATIONS IN LOCAL REINFORCEMENT RATE ON LOCAL RESPONSE RATE IN VARIABLE INTERVAL SCHEDULES
Authors: Leslie Julian C.
Published: March 2006

Rats trained to lever press for sucrose were exposed to variable‐interval schedules in which (i) the probability of reinforcement in each unit of time was a constant, (ii) the probability was high in the first ten seconds after reinforcement and low thereafter, (iii) the probability was low for ten seconds and high thereafter, (iv) the probability increased with time since reinforcement, or (v) the probability was initially zero and then increased with time since reinforcement. All schedules generated similar overall reinforcement rates. A peak in local response rate occurred several seconds after reinforcement under those schedules where reinforcement rate at this time was moderate or high ([i], [ii], and [iv]). Later in the inter‐reinforcement interval, local response rate was roughly constant under those schedules with a constant local reinforcement rate ([i], [ii], and [iii]), but increased steadily when local reinforcement rate increased with time since reinforcement ([iv] and [v]). Postreinforcement pauses occurred on all schedules, but were much longer when local reinforcement rate was very low in the ten seconds after reinforcement ([iii]). The interresponse time distribution was highly correlated with the distribution of reinforced interresponse times, and the distribution of postreinforcement pauses was highly correlated with the distribution of reinforced postreinforcement pauses on some schedules. However, there was no direct evidence that these correlations resulted from selective reinforcement of classes of interresponse times and pauses.
AN INTERRESPONSE TIME ANALYSIS OF VARIABLE‐RATIO PUNISHMENT
Authors: Lande Stephen D.
Published: March 2006

An interresponse time analysis was used to study the effects of variable‐ratio punishment schedules on the temporal pattern of reinforced responding. Twelve pigeons responded on a baseline variable‐interval schedule of food reinforcement. A variable‐ratio ten schedule of electric shock punishment was then introduced. The shock intensity was systematically increased to the highest intensity at which responding could be maintained. At this intensity, the mean variable‐ratio value was increased and then decreased. Variable‐ratio punishment resulted in an increased relative frequency of very short unreinforced interresponse times (response bursting). Increased response bursting accounted for instances of response rate facilitation. In addition, shock was followed by interresponse times of decreasing mean length over the first several responses after shock.
THE DELAY‐REDUCTION HYPOTHESIS OF CONDITIONED REINFORCEMENT AND PUNISHMENT: OBSERVING BEHAVIOR
Authors: Case David A. , Fantino Edmund
Published: March 2006

Pigeons responded in an observing‐response procedure in which three fixed‐interval components alternated. Pecking one response key produced food reinforcement according to a mixed schedule. Pecking the second (observing) key occasionally replaced the mixed‐schedule stimulus with the stimulus correlated with the fixed‐interval component then in effect. In Experiment 1, observing was best maintained by stimuli correlated with a reduction in mean time to reinforcement. That finding was consistent with the conditioned‐reinforcement hypothesis of observing behavior. However, low rates of observing were also maintained by stimuli not representing delay reduction. Experiment 2 assessed the role of sensory reinforcement. It showed that response rate was higher when maintained by stimuli uncorrelated with reinforcement delay than when the stimuli were correlated with a delay increase. This latter result supports a symmetrical version of the conditioned‐reinforcement hypothesis that requires suppression by stimuli correlated with an increase in time to reinforcement. The results were inconsistent with hypotheses stressing the reinforcing potency of uncertainty reduction.
MELIORATION, MATCHING, AND MAXIMIZATION
Authors: Vaughan William
Published: March 2006

Pigeons were studied in an experiment involving two concurrently available response keys. Conditions were such that in the first condition the predictions of melioration (Herrnstein & Vaughan, 1980), minimization of deviation from matching, and maximization were identical: relative time on the right key should have fallen between .125 and .25, which in fact occurred. In the second condition, melioration predicted a shift in relative time on the right to between .75 and .875, which would involve a transient deviation from matching as well as a substantial drop in rate of reinforcement. All three birds eventually shifted their distribution of behavior to within the range predicted by melioration.
RESPONDING MAINTAINED UNDER INTERMITTENT SCHEDULES OF ELECTRIC‐SHOCK PRESENTATION: “SAFETY” OR SCHEDULE EFFCTS?
Authors: Malagodi E. F. , Gardner Michael L. , Ward Susan E. , Magyar Regis L.
Published: March 2006

Four experiments were conducted in which lever pressing by squirrel monkeys was maintained under multiple, mixed, or chained schedules of electric‐shock presentation. In the first two experiments, a multiple schedule was employed in which a fixed‐interval schedule of shock presentation alternated with a signaled two‐minute component. Initially, no events were scheduled during the two‐minute component (a safety period). In the first experiment, the safety period was “degraded” by introducing and systematically increasing the frequency of periodic shocks presented during that component. In the second experiment, the proportion of overall safe time to unsafe time was decreased by decreasing the value of the fixed‐interval schedule while holding constant shock frequency during the two‐minute component. In the third experiment, the overall arrangement was changed from a multiple to a mixed schedule in an attempt to determine whether fixed‐interval responding would be maintained when a single exteroceptive stimulus was associated with both components. In the fourth experiment, the overall arrangement was changed from a multiple to a chained schedule in an effort to determine whether fixed‐interval responding would be maintained when its consequence was presentation of a signaled “unsafe” period. Fixed‐interval responding was well maintained under all experimental conditions; the varied relationships obtained lend more support to conceptualizations of shock‐maintained behavior as exemplifying schedule‐controlled behavior than to suggestions that such behavior may be readily accounted for by “safety theory.”
EFFECTS OF RATIO CONTINGENCIES ON RESPONDING MAINTAINED BY SCHEDULES OF ELECTRIC‐SHOCK PRESENTATION (RESPONSE‐PRODUCED SHOCK)
Authors: Branch Marc N. , Dworkin Steven I.
Published: March 2006

Squirrel monkeys' lever pressing was established under fixed‐interval schedules of electric‐shock presentation (response‐produced shock). After appropriate temporal patterns of lever pressing were engendered, either fixed‐ratio schedules of shock presentation were added to the fixed interval, or yoked variable‐ratio schedules were substituted for the fixed‐interval schedules. When fixed‐ratio schedules were added, there was an initial rise in response rate and schedule‐appropriate patterns of responding developed. After many sessions, however, responding ceased abruptly, in some cases with remarkable quickness. When variable‐ratio schedules were substituted, responded declined gradually and eventually was poorly maintained. Ratio contingencies may not support responding as well as interval contingencies when electric shock is the maintaining event.
UNDERMATCHING AND OVERMATCHING: THE FIXED‐RATIO CHANGEOVER REQUIREMENT
Authors: Pliskoff Stanley S. , Fetterman J. Gregor
Published: March 2006

Concurrent variable‐interval two‐minute and six‐minute schedules were arranged while the fixed‐ratio changeover requirement was varied among one, two, and four responses. A four‐response requirement produced overmatching in the response and time data. A one‐response requirement produced consistent undermatching in the time data but mixed results in the response data. The two‐response requirement showed undermatching in the time data and overmatching in the response data. The results are discussed in relation to previous research using changeover requirements of five and ten responses, which produced clear tendencies toward overmatching, especially with response data. Taken together, these findings suggest that matching is not a unique result, and that undermatching or overmatching can be produced by continuous variation of the changeover requirements.
PREFERENCE FOR SIGNALED VERSUS UNSIGNALED REINFORCEMENT DELAY IN CONCURRENT‐CHAIN SCHEDULES
Authors: Marcattilio A. J. M. , Richards Ralph W.
Published: March 2006

A concurrent‐chain schedule was employed to examine pigeons' preferences for signaled versus unsignaled delay of reinforcement in which the delay durations ranged from zero to ten seconds. In general, pigeons preferred signaled delay over unsignaled delay especially when a variable‐interval 30‐second schedule operated in each initial link; when a variable‐interval 90‐second schedule operated in each initial link, these preferences tended toward indifference or were attenuated. In addition, prior training seemed to exert partial control over behavior. Responding in the terminal link was higher under signaled delay than unsignaled delay in a majority of the cases. Moreover, response rates under signaled delay remained fairly constant whereas responding under unsignaled delay was initially high, but decreased systematically with delay durations as short as 2.5 seconds. These results are consistent with a number of other studies demonstrating the significant role of a signal for impending positive stimuli.
THE ROLE OF DISCRIMINATIVE STIMULI IN CONCURRENT PERFORMANCES
Authors: Bourland Gordon , Miller James T.
Published: March 2006

Key pecking in pigeons was examined under concurrent and parallel arrangements of two independent and simultaneously available variable‐interval schedules. Pecks on the changeover key alternated the schedule of reinforcement for responses on the main key. Under concurrent schedules, discriminative stimuli were paired with the reinforcement schedule arranged in each component and changeover responses also alternated these stimuli. Under parallel schedules, changeover responses alternated the effective reinforcement schedule, but did not change the discriminative stimulus. On concurrent procedures, changeover response rate was inversely related to the difference in reinforcement rate between the two components, whereas on parallel schedules no consistent relationship was found. With both schedules, absolute response and reinforcement rates were positively related, although for a given set of reinforcement frequencies, rates were often higher on the concurrent schedules. On concurrent schedules, relative response rates and relative times were equal to relative reinforcement rates. On parallel schedules these ratios were positively related, but response and time ratios were much smaller than were obtained with comparable concurrent schedules. This inequality was most pronounced when absolute reinforcement frequencies were lowest.
CONDITIONED REINFORCEMENT AS A FUNCTION OF DURATION OF STIMULUS
Authors: Dinsmoor James A. , Mulvaney Dallas E. , Jwaideh Alice R.
Published: March 2006

Pigeons were provided with three keys. Pecking the center key produced grain on a schedule that alternated at unpredictable times between a variable‐interval component and extinction. On concurrent variable‐interval schedules, pecking either side key produced a stimulus associated with the variable‐interval component on the center key provided that said schedule was currently in effect. The independent variable was the length of time this stimulus remained on the keys. Pecking one side key produced the stimulus for 27 seconds, whereas the duration produced by pecking the other key varied for successive blocks of sessions. For the first four birds, the values tested were 3, 9, 27, and 81 seconds. For the second group, numbering three birds, the values tested were 1, 3, 9, and 27 seconds. The dependent variable was the proportion of total side key pecks that occurred on the variable key. For all birds, the function was positive in slope and negative in acceleration. This finding supports a formulation that ascribes the maintenance of observing responses in a normal setting to the fact that the subject exposes itself to the positive discriminative stimulus for a longer mean duration than it does to the negative stimulus.
TRACE AUTOSHAPING: ACQUISITION, MAINTENANCE, AND PATH DEPENDENCE AT LONG TRACE INTERVALS
Authors: Lucas Gary A. , Deich James D. , Wasserman Edward A.
Published: March 2006

The pigeon's tendency to acquire and maintain signal‐directed key pecking under a trace conditioning procedure was parametrically examined. In Experiment 1, the percentage of CS trials with a key peck response was a decreasing function of the trace interval for separate groups of pigeons. The majority of subjects acquired signal‐directed key pecking with trace intervals as long as 36 sec. In Experiment 2, differential maintenance of key pecking occurred across trace intervals in a within‐subject procedure. Maintenance of key pecking at 36‐ and 60‐sec trace intervals was path dependent in that responding depended on the subject's performance under the preceding trace interval.
CHOICE AND MULTIPLE REINFORCERS
Authors: Moore Jay
Published: March 2006

Pigeons chose between equivalent two‐component mixed and multiple terminal‐link schedules of reinforcement in the concurrent‐chains procedure. The pigeons preferred the multiple schedule over the mixed when the components of the compound schedules were differentiated in terms of density of reinforcement, but the pigeons were indifferent when the components were differentiated in terms of number of reinforcers per cycle. Taken together, these results indicate that a local variable, the interval to the first reinforcer, but not a molar variable, the number of reinforcers, was sufficient to differentiate the components and thereby evoke preference.
INDEPENDENCE OF RESPONSE FORCE AND REINFORCEMENT RATE ON CONCURRENT VARIABLE‐INTERVAL SCHEDULE PERFORMANCE
Authors: Hunter Ian , Davison Michael
Published: March 2006

Five pigeons were trained over 43 experimental conditions on a variety of concurrent variable‐interval schedules on which the forces required on the response keys were varied. The results were well described by the generalized matching law with log reinforcement ratios and log force ratios exerting independent (noninteractive) effects on preference. A further analysis using the Akaike criterion, an information‐theoretic measure of the efficiency of a model, showed that overall reinforcement rate and overall force requirement did not affect preference. Unlike reinforcement rate changes, force requirement increases did not change the response rate on the alternate key, and an extension of Herrnstein's absolute response rate function for force variation on a single variable‐interval schedule is suggested.
A SEARCH FOR SYMMETRY IN THE CONDITIONAL DISCRIMINATIONS OF RHESUS MONKEYS, BABOONS, AND CHILDREN
Authors: Sidman Murray , Rauzin Ricki , Lazar Ronald , Cunningham Sharon , Tailby William , Carrigan Philip
Published: March 2006

Procedures for generating arbitrary matching‐to‐sample performances may generate only conditional discriminations. Rational grounds for this distinction are proposed, based on the properties that any equivalence relation must possess. Empirical tests are described for determining whether subjects trained on conditional discriminations are also engaged in true matching to sample. A series of studies then leads to the conclusion that proof of true matching to sample by monkeys, pigeons, or baboons is yet to be provided. Whether the absence of such proof reflects experiential factors or species‐defined limitations is not presently clear.
POSITIVE AND NEGATIVE CONTRAST AS A FUNCTION OF COMPONENT DURATION FOR KEY PECKING AND TREADLE PRESSING
Authors: McSweeney Frances K.
Published: March 2006

Pigeons responded on several multiple schedules for food reinforcers. The duration of the components varied from four seconds to 16 minutes. The absolute size of positive (Experiment 1) and negative (Experiment 2) behavioral contrast varied inversely with component duration when key pecks produced the reinforcers. The absolute size of negative contrast varied directly with component duration, when treadle presses produced the reinforcers (Experiment 3). These results conform to theories that suggest that positive and negative contrast are symmetrical when pigeons peck keys. They also conform to theories that suggest that the same principles do not govern contrast when pigeons peck keys as when they press treadles. Finally, the results support the measurement of behavioral contrast by the differences between baseline rates of responding and the rates emitted when contrast is present.
SOME FACTORS THAT INFLUENCE THE ACQUISITION OF COMPLEX, STEREOTYPED, RESPONSE SEQUENCES IN PIGEONS
Authors: Pisacreta Richard
Published: March 2006

Two pigeons were required to peck six to nine illuminated response keys. A response on any one of the keys darkened that key. When each key had been darkened, a reinforcer was delivered. No specific sequence of key pecking was ever required. The keys were presented in various matrices: three by two, three by three, horizontal rows, and vertical columns. The keys either presented the same stimulus, white light; or each key presented a different stimulus, a color or form. The results indicated that although there were 720 to 362,880 different sequences that would produce reinforcement, each bird developed a particular, stereotyped sequence that dominated its behavior. Variability among the birds across phases yielded less than 60 sequences, .0001 to 6 percent of the possible sequences. The data suggest that a reinforcement contingency that includes “free choice” of response sequence will produce stereotypical response sequences that function as complex “units” of behavior.
CHOICE BEHAVIOR OF RATS IN A CONCURRENT‐CHAINS SCHEDULE: AMOUNT AND DELAY OF REINFORCEMENT
Authors: Ito Masato , Asaki Kazue
Published: March 2006

Rats were exposed to concurrent‐chains schedules in which the terminal links were equal fixed‐interval schedules terminating in one or three food pellets. Choice proportions for large reward increased with increases in delay intervals programmed on fixed‐interval schedules and supported the predictions derived from a general choice model originally formulated by Fantino and later developed by Navarick and Fantino. In addition, a functional equivalence of two alternatives was established by increasing delay intervals with large reward, whereas delay intervals for small reward were held constant. Functionally equivalent delay intervals with large reward, for each delay interval with small reward, can be described by a power function with exponent smaller than 1.0. A better prediction of choice proportions resulted when this function was used to derive predicted choice proportions.
ON THE EFFECTS OF COMPONENT DURATIONS AND COMPONENT REINFORCEMENT RATES IN MULTIPLE SCHEDULES
Authors: Charman Lesle , Davison Michael
Published: March 2006

Four experiments, each using the same six pigeons, investigated the effects of varying component durations and component reinforcement rates in multiple variable‐interval schedules. Experiment 1 used unequal component durations in which one component was five times the duration of the other, and the shorter component was varied over conditions from 120 seconds to 5 seconds. The schedules were varied over five values for each pair of component durations. Sensitivity to reinforcement rate changes was the same at all component durations. In Experiment 2, both component durations were 5 seconds, and the schedules were again varied using both one and two response keys. Sensitivity to reinforcement was not different from the values found in Experiment 1. In Experiment 3, various manipulations, including body‐weight changes, reinforcer duration changes, blackouts, hopper lights correlated with keylights, and overall reinforcement rate changes were carried out. No reliable increase in reinforcement sensitivity resulted from any manipulation. Finally, in Experiment 4, reinforcement rates in the two components were kept constant and unequal, and the component durations were varied. Shorter components produced significantly increased response rates normally in the higher reinforcement rate component, but schedule reversals at short component durations eliminated the response rate increases. The effects of component duration on multiple schedule performance cannot be interpreted as changing sensitivity to reinforcement nor to changing bias.
PAUSING UNDER VARIABLE‐RATIO SCHEDULES: INTERACTION OF REINFORCER MAGNITUDE, VARIABLE‐RATIO SIZE, AND LOWEST RATIO
Authors: Schlinger Henry , Blakely Elbert , Kaczor Thomas
Published: March 2006

Pigeons pecked a key under two‐component multiple variable‐ratio schedules that offered 8‐s or 2‐s access to grain. Postreinforcement pausing and the rates of responding following the pause (run rates) in each component were measured as a function of variable‐ratio size and the size of the lowest ratio in the configuration of ratios comprising each schedule. In one group of subjects, variable‐ratio size was varied while the size of the lowest ratio was held constant. In a second group, the size of the lowest ratio was varied while variable‐ratio size was held constant. For all subjects, the mean duration of postreinforcement pausing increased in the 2‐s component but not in the 8‐s component. Postreinforcement pauses increased with increases in variable‐ratio size (Group 1) and with increases in the lowest ratio (Group 2). In both groups, run rates were slightly higher in the 8‐s component than in the 2‐s component. Run rates decreased slightly as variable‐ratio size increased, but were unaffected by increases in the size of the lowest ratio. These results suggest that variable‐ratio size, the size of the lowest ratio, and reinforcer magnitude interact to determine the duration of postreinforcement pauses.
THE EFFECTS OF REINFORCEMENT FREQUENCY AND RESPONSE REQUIREMENTS ON THE MAINTENANCE OF BEHAVIOR
Authors: Rider David P. , D'Angelo Brian J.
Published: March 2006

Six rats responded under fixed‐interval and tandem fixed‐interval fixed‐ratio schedules of food reinforcement. Basic fixed‐interval schedules alternated over experimental conditions with tandem fixed‐interval fixed‐ratio schedules with the same fixed‐interval value. Fixed‐interval length was varied within subjects over pairs of experimental conditions; the ratio requirement of the tandem schedules was varied across subjects. For both subjects with a ratio requirement of 10, overall response rates and running response rates typically were higher under the tandem schedules than under the corresponding basic fixed‐interval schedules. For all subjects with ratio requirements of 30 or 60, overall response rates and running response rates were higher under the tandem schedules than under the corresponding basic fixed‐interval schedules only with relatively short fixed intervals. At longer fixed intervals, higher overall response rates and running rates were maintained by the basic fixed‐interval schedules than by the tandem schedules. These findings support Zeiler and Buchman's (1979) reinforcement‐theory account of response strength as an increasing monotonic function of both the response requirement and reinforcement frequency. Small response requirements added in tandem to fixed‐interval schedules have little effect on reinforcement frequency and so their net effect is to enhance responding. Larger response requirements reduce reinforcement frequency more substantially; therefore their net effect depends on the length of the fixed interval, which limits overall reinforcement frequency. At the longest fixed intervals studied in the present experiment, reinforcement frequency under the tandem schedules was sufficiently low that responding weakened or ceased altogether.
INCOME MAXIMIZING ON CONCURRENT RATIO‐INTERVAL SCHEDULES OF REINFORCEMENT
Authors: Shurtleff David , Silberberg Alan
Published: March 2006

Three experiments examined the effect of food availability on pigeons' choice behavior under concurrent schedules of reinforcement. In Experiment 1, 3 pigeons earned their daily food ration by choosing, in 30‐min sessions, between concurrent variable‐ratio 30 variable‐interval 40‐s schedules. Food presentations during both schedules lasted 2 or 12 s, depending upon the condition. Relative variable‐ratio response rate was inversely related to hopper duration. In Experiment 2, 4 pigeons received their daily feeding by responding on the same schedule pair as in Experiment 1 (with 4‐s food presentations) in sessions that varied in length from 10 to 30 min, depending on the condition. The length of a vertical slit projected on a response key increased with time so that “passage of time” might be more easily discriminable. As session duration decreased, relative variable‐ratio response rate increased. In Experiment 3, 4 pigeons chose between two variable‐interval 40‐s schedules. One schedule operated without regard to the schedule selected, whereas the other operated only when the subject responded in its presence (dependent). Although these schedules had the same feedback function, preference for the dependent variable interval increased as session duration decreased from 30 to 10 min. The preference changes in these studies reveal the operation of an income‐maximizing process in choice.
HUMANS' SENSITIVITY TO VARIATION IN REINFORCER AMOUNT: EFFECTS OF THE METHOD OF REINFORCER DELIVERY
Authors: King George R. , Logue A. W.
Published: March 2006

Two experiments examined human subjects' sensitivity to variation in reinforcer amount under different methods of reinforcer delivery. Subjects chose between schedules varying in terms of amount and/or delay of reinforcement, the reinforcer being points exchangeable for money. In Experiment 1, reinforcer amount was manipulated by varying the monetary value of the points across conditions while the number of seconds of access to a consummatory response remained constant. Choice was strongly sensitive to reinforcer amount and indicative of self‐control, as in previous experiments. In Experiment 2, reinforcer amount was manipulated by automatically delivering different numbers of points during the amount period, and the consummatory response was eliminated. Sensitivity to variation in reinforcer amount was significantly lower than in Experiment 1. Furthermore, the subjects in Experiment 2 exhibited significantly less self‐control than did the subjects in Experiment 1. Humans' sensitivity to variation in reinforcer amount appears to be affected by factors that enhance the discriminability of the consequences of responding.
FREE BIRDS AREN'T FAT: WEIGHT GAIN IN CAPTURED WILD PIGEONS MAINTAINED UNDER LABORATORY CONDITIONS
Authors: Poling Alan , Nickel Mark , Alling Ken
Published: March 2006

Nine feral pigeons, 5 from an urban setting and 4 from a rural setting, were captured and maintained for 42 days under free‐feeding conditions comparable to those arranged for laboratory subjects. On average, birds increased their body weights by 17% over this period. The range of increase across birds was 9 to 30%. These findings suggest that the food deprivation arranged for laboratory pigeons, which is characteristically 80% of free‐feeding weights, may in some sense be less severe than it first appears.
EQUIVALENCE CLASSES GENERATED BY SEQUENCE TRAINING
Authors: Sigurdardottir Z. Gabriela , Green Gina , Saunders Richard R.
Published: March 2006

In Experiment 1, 3 adult females were taught with verbal instructions and contingencies to select, in sequence, three arbitrary visual stimuli from an array of five stimuli. After four different sequences were taught, match‐to‐sample tests assessed emergent conditional relations among all stimuli that had been selected in the same order in the sequences. Subjects' performances indicated development of four stimulus classes, three based on ordinal position and one based on nonselection. Next, match‐to‐sample training established conditional relations between each of four novel figures and one member of each of the ordinal stimulus classes. Tests confirmed that the classes were equivalence classes, each expanded by one new member. In subsequent sequence tests, the new stimuli were selected in a sequence that was consistent with ordinal class membership. Experiment 2 replicated Experiment 1 with 2 different adult females, but the verbal instructions were omitted. Results were similar to Experiment 1, except that extensive review and retesting were required before expansion of the ordinal classes with the novel figures was observed.
THE HISTORY OF IMITATION IN LEARNING THEORY: THE LANGUAGE ACQUISITION PROCESS
Authors: Kymissis Effie , Poulson Claire L.
Published: March 2006

The concept of imitation has undergone different analyses in the hands of different learning theorists throughout the history of psychology. From Thorndike's connectionism to Pavlov's classical conditioning, Hull's monistic theory, Mowrer's two‐factor theory, and Skinner's operant theory, there have been several divergent accounts of the conditions that produce imitation and the conditions under which imitation itself may facilitate language acquisition. In tracing the roots of the concept of imitation in the history of learning theory, the authors conclude that generalized imitation, as defined and analyzed by operant learning theorists, is a sufficiently robust formulation of learned imitation to facilitate a behavior‐analytic account of first‐language acquisition.
THE UTILITY OF VERBAL AND BEHAVIORAL ASSESSMENTS OF VALUE
Authors: Bernstein Daniel J. , Michael Renee L.
Published: March 2006

Subjects lived in a laboratory apartment for up to 30 days, engaging in ordinary activities such as reading, sewing, and artwork. The amount of time devoted to each activity was recorded and compared with periodic verbal ratings of the amount of time devoted to the activities. The verbal and observational assessments of the time distribution were very similar, but there were some discrepancies. Based on self‐reports and on observation of time actually devoted to the activities, contingencies were arranged in which time devoted to one activity produced time available for a second activity. When the contingency relation was based on behavioral assessment, predictions of time redistribution were more accurate than when the relations were based on verbal assessment. The close correspondence between observed distributions of time and verbally assessed distributions was probably due to the well‐specified situation and rigorous assessment methods. Contrary to some cognitive‐behavioral accounts, the contingency results suggest that verbal assessment is not necessarily preferable to observation when the two make discrepant predictions. It is suggested that verbal reports might be used more often in behavior analysis in place of lengthy or difficult observations, and attention is drawn to a personality model that parallels important components of behavior analysis.
PERFORMANCE OF CHILDREN UNDER A MULTIPLE RANDOM‐RATIO RANDOM‐INTERVAL SCHEDULE OF REINFORCEMENT
Authors: Baxter Gregg A. , Schlinger Henry
Published: March 2006

Three children, aged 1.5, 2.5, and 4.5 years, pressed telegraph keys under a two‐component multiple random‐ratio random‐interval schedule of reinforcement. In the first condition, responses on the left key were reinforced under a random‐interval schedule and responses on the right key were reinforced under a random‐ratio schedule. In the second condition, the schedule components were reversed. In the third condition, the original arrangement was reinstated. For all subjects, rates of responding were higher in the random‐ratio component despite higher rates of reinforcement in the random‐interval component. The average interreinforcement interval of the random‐interval component was increased in the fourth condition, resulting in more similar rates of reinforcement for both schedule components, and then returned to its original value in the fifth condition. In both conditions, all subjects continued to exhibit higher rates of responding in the ratio component than in the interval component. Although these observations are consistent with results from studies with pigeons, it is argued that the response‐rate differences between the interval and ratio schedule components are sufficient to demonstrate schedule sensitivity.
CATEGORY DISCRIMINATION BY PIGEONS USING FIVE POLYMORPHOUS FEATURES
Authors: Fersen Lorenzo von , Lea Stephen E. G.
Published: March 2006

Eight pigeons were trained to discriminate between sets of color photographs of natural scenes. The scenes differed along five two‐valued dimensions (site, weather, camera distance, camera orientation, and camera height), and all combinations of the feature values were used. One value of each dimension was designated as positive, and slides containing three or more positive feature values were members of the positive stimulus set. Thus, each feature had an equal, low, correlation with reinforcement, and all features had zero correlations with each other. Seven of the 8 pigeons learned this discrimination, and their responding came under the control of all five features. Within the positive and negative stimulus sets, response rates were higher to stimuli that contained more positive feature values. Once discrimination had been achieved, reversal training was given using a subset of the slides. In this subset, only a single feature was correlated with reinforcement. All pigeons learned this reversal successfully and generalized it to additional photographs with the same feature content. After reversal, the original reinforcement contingencies were reinstated, and training was continued using all the slides except those that had been used in reversal. Reversal generalized to these slides to some extent. Analysis of the response rates to individual slides showed that, compared with prereversal training, only the feature that had been subjected to reversal contingencies showed a reversed correlation with response rate. The remaining features showed the same correlation with response rate as they had before reversal training. Thus, reversal on some members of a category following category discrimination training led to generalization to stimuli within the category that were not involved in the reversal, but not to features that were not reversed. It is therefore inappropriate to refer to the pigeons as learning a concept.
THE ESTABLISHMENT OF STIMULUS CONTROL BY INSTRUCTIONS AND BY DIFFERENTIAL REINFORCEMENT
Authors: Danforth Jeffrey S. , Chase Philip N. , Dolan Mark , Joyce James H.
Published: March 2006

A repeated acquisition design was used to study the effects of instructions and differential reinforcement on the performance of complex chains by undergraduates. The chains required responding on a series of keys that corresponded to characters that appeared on a monitor. Each day, subjects performed a new chain in a learning session and later relearned the same chain in a test session. Experiment 1 replicated previous research by showing that instructional stimuli paired with the correct responses in the learning sessions, combined with differential reinforcement in both learning and test sessions, resulted in stimulus control by the characters in each link. Experiment 2 separated the effects of instructional stimuli and differential reinforcement, and showed that stimulus control by the characters could be established solely by differential reinforcement during the test sessions. Experiment 3 showed that when a rule specified the relation between learning and test sessions, some subjects performed accurately in the test sessions without exposure to any differential consequences. This rule apparently altered the stimulus control properties of the characters much as did differential reinforcement during testing. However, compared to differential reinforcement, the rule established stimulus control more quickly.
RESPONSE SPECIFICITY IN ANIMAL TIMING
Authors: Durlach Paula J. , Dawson Gerard R.
Published: March 2006

The stimuli that control responding in the peak procedure were investigated by training rats, in separate sessions, to make two different responses for food reinforcement. During one type of session, lever pressing was normally reinforced 32 s after the onset of a light. During the other type of session, chain pulling was normally reinforced either 8 s after the onset of one auditory cue or 128 s after the onset of a different auditory cue. For both types of sessions, only the appropriate manipulandum was available, and 20% of the trials lasted 240 s and involved no response‐contingent consequences. Rats were then tested with the auditory cues in the presence of the lever and the light in the presence of the chain. If the time of reinforcement associated with each stimulus was learned, response rates should peak at these times during transfer testing. However, if a specific response pattern was learned for each stimulus, little transfer should occur. The results did not clearly support either prediction, leading to the conclusion that both a representation of the time of reinforcement and the rat's own behavior may control responding in this situation.
EFFECTS OF REINFORCING PRESELECTED APPROXIMATIONS ON THE TOPOGRAPHY OF THE RAT'S BAR PRESS
Authors: Stokes Patricia D. , Balsam Peter D.
Published: March 2006

The effects of different shaping approximations on the topography of the rat's bar press were investigated in two experiments. Behavior was classified into discrete components, and changes in components and their sequential organization were analyzed. Experiment 1 examined response form early in training and found that specific components reinforced during shaping were incorporated into press sequences. Experiment 2 investigated how response form changed when a shaping contingency was relaxed later in training. Two topographies were selected for reinforcement, and both appeared in the press sequences of all subjects by the end of shaping. Subsequently, all variations of bar pressing were reinforced, and neither topography was necessary to satisfy the contingency. Although the frequency of the topographies reinforced during shaping declined for 3 of 4 subjects during this phase, the most frequent press sequence for 2 rats at the end of training included both unnecessary topographies. Variability in press topographies declined when all emitted variants were reinforced. However, all subjects emitted novel response forms throughout training. The results demonstrate that specific response‐reinforcer contingencies influence response form by modulating component availability and organization.
EFFECTS OF DISCRETE‐TRIAL AND FREE‐OPERANT PROCEDURES ON THE ACQUISITION AND MAINTENANCE OF SUCCESSIVE DISCRIMINATION IN RATS
Authors: Hachiya Shin , Ito Masato
Published: March 2006

Rats were trained on a successive discrete‐trial discrimination between two tonal stimuli to examine the effects of availability of a lever during intertrial intervals. In the discrete‐trial condition, in which a lever was removed from the chamber during intertrial intervals, 10‐s trials were initiated by the presentation of both discriminative stimulus and lever. In the free‐operant condition, in which a lever was present during both trials and intertrial intervals, 10‐s trials were initiated only by the presentation of a discriminative stimulus. Experiment 1 employed 50‐s intertrial intervals and demonstrated that discriminative performances were acquired faster and maintained better in the free‐operant conditions than in the discrete‐trial conditions. Experiment 2 employed 5‐s intertrial intervals and showed that poor discriminative performances in the discrete‐trial conditions were improved. These results indicate that the presentation of a lever to start a trial can overshadow or mask the control by a discriminative stimulus and thereby obstruct the acquisition and maintenance of discriminative performances. Furthermore, the overshadowing or masking effects are strengthened as a function of the duration of intertrial intervals.
THE EFFECTS OF SCHEDULE HISTORY AND THE OPPORTUNITY FOR ADJUNCTIVE RESPONDING ON BEHAVIOR DURING A FIXED‐INTERVAL SCHEDULE OF REINFORCEMENT
Authors: Johnson Lisa M. , Bickel Warren K. , Higgins Stephen T. , Morris Edward K.
Published: March 2006

The effects of schedule history and the availability of an adjunctive response (polydipsia) on fixed‐interval schedule performance were investigated. Two rats first pressed levers under a schedule of food reinforcement with an interresponse time greater than 11 s, and 2 others responded under a fixed‐ratio 40 schedule. All 4 were then exposed to a fixed‐interval 15‐s schedule. Water was continuously available under these conditions, but after responding became stable on the fixed‐interval schedule, access was experimentally manipulated. With water freely available, subjects did not display characteristic fixed‐interval response rates and patterns (i.e., scalloping or break‐and‐run). Instead, they exhibited predictable, stable patterns of behavior as a function of their schedule histories: Subjects with the interresponse‐time history exhibited low response rates, and those with the fixed‐ratio history exhibited high rates. Manipulating the amount of water available resulted in marked changes in response rates for rats with the interresponse‐time history but not for those with the fixed‐ratio history. The results illustrate the multiple causation of behavior by its previous and current schedules of reinforcement and other concurrent factors.
VIOLATIONS OF STOCHASTIC TRANSITIVITY ON CONCURRENT CHAINS: IMPLICATIONS FOR THEORIES OF CHOICE
Authors: Houston Alasdair
Published: March 2006

The concurrent‐chains procedure has been used to measure how choice depends on various aspects of reinforcement, such as its delay and its magnitude. Navarick and Fantino (1972, 1974, 1975) have found that choice in this procedure can violate the condition of stochastic transitivity that is required if a unidimensional scale for reinforcements is to be possible. It is shown in this paper that two simple unidimensional models of choice on concurrent chains can produce violations of stochastic transitivity. It is argued that such violations may result from the complex contingencies of the concurrent‐chains procedure.
CHOICE, CHANGEOVER, AND TRAVEL: A QUANTITATIVE MODEL
Authors: Davison Michaelm
Published: March 2006

Six pigeons were trained on concurrent variable‐interval schedules in which responding on fixed‐interval schedules was required to give access to the alternate schedule. Responding on the concurrent schedules was not allowed, after changing over had commenced, until the changeover schedule had been completed. In Parts 1 to 3 of the experiment, the changeover fixed‐interval schedules were equal and were 0 s, 10 s, and 20 s, respectively. In each part, the relative frequency of reinforcement obtained on the concurrent schedules was varied over at least five conditions. In Part 4, the concurrent schedules were equal, and one changeover fixed‐interval schedule was twice the other. Under these conditions, the absolute sizes of the changeover schedules were varied. Increasing the changeover requirement from 0 s to 10 s (Parts 1 and 2) resulted in increases in the sensitivity of behavior allocation to reinforcers obtained, but no further increase was obtained when the changeover schedules were increased to 20 s (Part 3). In Part 4, performance was biased towards the concurrent schedule that took less time to enter. These results are consistent with a subtractive punishment model of travel in which the degree of punishment is measured by the number of reinforcers apparently lost from a schedule when the subject changes to that schedule. Absolute times spent on the main keys could be accurately described by a previous model of changeover performance.
THE RELATIONSHIP BETWEEN FEEDING RATE AND PATCH CHOICE
Authors: Johnson Deanne F. , Collier George
Published: March 2006

Rats in a laboratory foraging simulation searched for sequential opportunities to feed in two patches that differed in the rate at which food pellets were delivered (controlled by fixed‐interval schedules) and in the size of the pellets. The profitability of feeding in each patch was calculated in terms of time (grams per minute) and in terms of effort (grams per bar press). These values were the result of the imposed fixed interval, the size of the pellets, and the rate at which the rats pressed the bar in each condition. The rats ate more food and larger meals, but not more frequent meals, at the patch offering the higher rate of food consumption, calculated as grams per minute. The relative intake at any patch was a function of the relative rate of intake during meals at that patch compared to the other patch. Rats respond to explicit manipulations of feeding time in the same manner as they respond to manipulations of feeding effort.
BEHAVIOR‐DEPENDENT REINFORCER‐RATE CHANGES IN CONCURRENT SCHEDULES: A FURTHER ANALYSIS
Authors: Davison Michael , Alsop Brent
Published: March 2006

Six pigeons were trained on concurrent variable‐interval schedules in three different procedures. The first procedure was a standard concurrent schedule, and the relative reinforcer frequency for responding was varied. The second was a schedule in which a relative left‐key response rate (over a fixed period of time) exceeding .75 produced, in the next identical time period a higher reinforcer rate on the right key. If this criterion was not exceeded, equal reinforcer rates were arranged on the two keys in this period. This was the dependent procedure. In the third (independent) procedure, the periods of higher right‐key reinforcer rates occurred with the same probability as in the second procedure, but occurred independently of behavior. In the second and third procedures, the fixed‐time period (window) was varied from 5 s to 60 s, and to 240 s in the second procedure only. Performance on the two keys was similar in the concurrent and independent procedures. The procedure used in the dependent conditions generally affected performance when the windows were shorter than about 30 s. Models of performance that assume that subjects do not discriminate changes in local relative reinforcer rates cannot account for the data. Moreover, existing models are inherently unable to account for the effects of contingencies of reinforcement between responding on one alternative and gaining reinforcers on another that are arranged or that emerge as a result of time allocated to alternative schedules. Undermatching on concurrent variable‐interval schedules may result from such emergent contingencies.