Pigeon Subjects Research Articles

Assessing potential reinforcement-like effects of brief stimuli unrelated to food reinforcers.

It is widely assumed that reinforcers are biologically relevant stimuli, or stimuli that have been associated with biologically relevant stimuli. However, brief, arbitrary stimuli have also been reported to have reinforcement-like effects, despite being unrelated to biologically relevant stimuli like food. The present study explored the potential reinforcement-like effects of brief stimuli across 5 experiments. In Experiments 1 through 4, pigeon subjects responded for food reinforcement and brief stimulus presentations in a 2-component multiple schedule. Neither baseline response rates nor resistance to change during disruption tests were systematically greater in a component with versus without brief stimulus presentations. Increasing the rate and duration of brief stimulus presentations in Experiment 4 did not reveal reinforcement-like effects when compared directly with food. In Experiment 5, pigeons chose between independent terminal links in a concurrent-chains procedure. Across conditions, varying the location, duration, and rate of brief stimulus presentations in the terminal links had no systematic effects on preference. In contrast, varying rates of food reinforcers resulted in large and reliable shifts in preference. Therefore, the present study found no systematic evidence that brief stimuli unrelated to food reliably increase response rates, resistance to change, or preference. These data demonstrate the value of systematic replication, and a behavioral momentum approach to assessing potential reinforcement-like effects.

The nanoeconomics of concurrent choice behavior.

We introduce to behavior analysis a way of analyzing choice behavior that exploits recent developments in nanoeconomics, financial economics, and econometrics. A response return, modeled on an economic return, is the log differenced count of responses allocated to each of two alternatives during a short time window, compared with that in the immediately preceding window. The response return is a new dependent variable which offers a novel and useful way of looking at operant behavior, especially at the molecular level of analysis. The response-return series is a near-instantaneous measure of an organism's dynamic preferences for each of two alternatives. Analyzing such a series requires time-analytic techniques, including Auto-Regressive Conditional Heteroskedastic (ARCH) models. We illustrate these techniques by analyzing choices between combinations of arithmetic and exponential variable-interval schedules with pigeon subjects. All response-return series were well-fitted by one of three ARCH-family models. The fitted models were differentially sensitive to transition versus steady-state data samples. The particular insights that the ARCH analyses offer are improved understanding of the effects of the instantaneous effects of reinforcers and their absence, of how the distribution of reinforcers in time affects choice, and of the differences between choice in transition and at steady state.

Within-Subject Renewal in Sign Tracking

Three sign-tracking experiments using pigeon subjects examined the contextual dependence of extinction after conditioning. Renewal of extinguished responding occurred when testing occurred in a different context, using a variety of different renewal designs. In each case, a within-subject design ensured that the various contexts were equivalent in their general treatment histories and differed only in whether or not a particular stimulus had been extinguished in their presence. These results strengthen the view that extinction is relatively context specific.

Occasion Setters: Specificity to the US and the CS–US Association

Two experiments using pigeon subjects examined whether the action of a positive occasion setter was specific to a particular CS–US association. In both experiments subjects were trained on a switching procedure, in which a diffuse feature, A, signaled that keylight x would be followed by one reinforcer, US1, and that a second keylight y would be followed a different reinforcer, US2. A second feature, B, signaled the converse arrangement, that x would be followed by US2 and y by US1. The intention was to establish whether the features allowed the birds to anticipate the specific keylight/US associations that they signaled. This was achieved using a blocking technique, by examining the ability of feature A to prevent learning about two test stimuli, S and D, presented in compound with x. On same trials A signaled stimulus x, which was followed, as in training, by US1; on these trials x was accompanied by S. On different trials x was signaled by A but followed by the other reinforcer, US2, and accompanied by the second test stimulus, D. If A signaled specific CS–US associations, then the US would be predicted in the former case but surprising in the latter, so that acquisition of associative strength by stimulus S would be blocked, but acquisition by stimulus D would not. In both experiments stimulus S supported less conditioned responding than stimulus D, which is consistent with this interpretation. The implications of these findings for theories of occasion setting are discussed.

Token reinforcement, choice, and self-control in pigeons.

Pigeons were exposed to self-control procedures that involved illumination of light-emitting diodes (LEDs) as a form of token reinforcement. In a discrete-trials arrangement, subjects chose between one and three LEDs; each LED was exchangeable for 2-s access to food during distinct posttrial exchange periods. In Experiment 1, subjects generally preferred the immediate presentation of a single LED over the delayed presentation of three LEDs, but differences in the delay to the exchange period between the two options prevented a clear assessment of the relative influence of LED delay and exchange-period delay as determinants of choice. In Experiment 2, in which delays to the exchange period from either alternative were equal in most conditions, all subjects preferred the delayed three LEDs more often than in Experiment-1. In Experiment 3, subjects preferred the option that resulted in a greater amount of food more often if the choices also produced LEDs than if they did not. In Experiment 4, preference for the delayed three LEDs was obtained when delays to the exchange period were equal, but reversed in favor of an immediate single LED when the latter choice also resulted in quicker access to exchange periods. The overall pattern of results suggests that (a) delay to the exchange period is a more critical determinant of choice than is delay to token presentation; (b) tokens may function as conditioned reinforcers, although their discriminative properties may be responsible for the self-control that occurs under token reinforcer arrangements; and (c) previously reported differences in the self-control choices of humans and pigeons may have resulted at least in part from the procedural conventions of using token reinforcers with human subjects and food reinforcers with pigeon subjects.

Summation in autoshaping

Pigeon subjects received Pavlovian conditioning with stimulus elements and were then tested with compounds of those elements. Experiments 1–3 used localized keylight elements and found no evidence for greater responding to the compound than to the elements. Experiments 4A–4D found evidence for greater second-order conditioning by a compound of two elements than by the elements themselves when the elements consisted of two diffuse stimuli or one diffuse stimulus and one localized keylight. No greater second-order conditioning resulted from a compound of two localized keylight elements, suggesting the possibility of perceptual interactions that reduce identification of the elements in the compound. Experiment 6 found evidence of summation when that interaction was reduced by sequential presentation. However, one attempt to capture this interaction in terms of configural conditioning (Pearce, 1987) failed to receive confirmation. These results suggest that the localized stimuli conventionally employed in autoshaping experiments may show such substantial perceptual interaction as to recommend against their routine use for studying conditioning in compounds.

Modulation of trained and extinguished stimuli by facilitators and inhibitors

Pigeon subjects received training of a diffuse stimulus as either a conditioned inhibitor or a conditioned facilitator of a keylight signal for food. The ability of these diffuse stimuli to modulate responding was then assessed with two other keylights that were undergoing discrimination reversal. At a point where responding was equivalent for the two targets, the modulators had a greater impact on the target undergoing extinction than on the target undergoing acquisition. These results have implications for the nature of modulation and extinction.

Intuitive statistical inference: An “irrational” context effect in college students’ categorization of binomial samples

College students learned to earn points by categorizing binomial samples produced by two equally likely and complementary random processes. To facilitate cross-species comparisons, the procedure was made to resemble an experiment with pigeon subjects (Shimp & Hightower, 1990). Samples were 1, 2, 4, or 8 successively presented outcomes (vertical or horizontal lines) of, in effect, tossing one of two equally likely coins, one coin (A) biased in favor of vertical and the other coin (B) similarly biased in favor of horizontal. Choosing red or green stimuli presented after each sample was reinforced if coin A or B had been tossed, respectively. The statistical diagnosticity of a sample, the relative likelihood of its having been produced by a particular coin, was varied by the bias on the coins and by sample size. Subjects became more conservative in the use of statistical information in a sample as the average diagnosticity of other samples (due to the bias on the coins) decreased. Except for this “irrational” context effect, the results qualitatively resembled those in the corresponding experiment with pigeons.

Transfer of inhibition and facilitation mediated by the original target stimulus

An autoshaping paradigm with pigeon subjects was used to study two-types-of modulation: facilitation and inhibition. In each paradigm, a diffuse stimulus signaled when a keylight would be reinforced. Transfer of that diffuse stimulus to a different keylight was assessed after the response-evoking power of the original keylight had been altered in the presence of a different modulator. That alteration of the original target produced a specific change in the transfer of modulators trained with that target. The results are interpreted as suggesting that transfer to another target stimulus is partly mediated by the association of the original target with the reinforcer. They are inconsistent with at least one version of a configurai cue interpretation.

Generalization of visual matching and delayed matching by a California sea lion (Zalophus californianus)

Only a limited number of species have been found capable of generalized matching-to-sample (MTS) after exposure to relatively few training exemplars. We trained a juvenile, experimentally naive California sea lion (Zalophus californianus) in MTS, using a pair of three-dimensional objects as samples. Successful matching to a criterion of 90% correct or better over 2 successive sessions was attained in 12 sessions (269 trials and 70 errors). Two subsequent “partial” transfer tests, in which each of the two training objects was paired with a novel test object, and four additional transfer tests, all with novel objects, were presented following training. An 80% performance criterion over 2 successive sessions was reached, or closely approximated, in from 2 to 4 transfer sessions for all transfer tests; errors to criterion tended to be reduced across the successive novel transfer tests and were as few as five during the final two tests; and performance on the first 48 trials of the last two novel transfers was not significantly different from a near-ceiling level baseline performance measure. Neophobic responses of the sea lion to new objects precluded an unbiased evaluation of immediate (Trial 1) transfer. The sea lion’s short-term memory for sample objects was also measured. Matching performance was maintained at a level of 78% correct responses or better for delays through to 45 sec after removal of the sample object. At a 58-sec delay, the longest tested, performance declined to 69% correct responses. These retention levels are only somewhat below levels reported for dolphins and nonhuman primates tested on visual delayed MTS, but they are above levels typically reported for pigeon subjects.

Perceptual masking of drug stimuli

AbstractThree separate drug‐discrimination experiments, using pigeon subjects, were designed to assess the modification of a morphine (MS) stimulus by d‐amphetamine (AMPH). Experiment 1 examined the drug mixture in a two‐choice discriminative procedure in three groups of subjects trained to one of three doses of MS (1.0, 3.2, or 10 mg/kg) vs. saline (SAL). Blockade of the MS stimulus by concomitant AMPH administration was training dose‐dependent. Complete blockade was found in the high‐MS (10 mg/kg) training dose (TD) group; partial blockade was found in the intermediate‐TD (3.2 mg/kg) group; and complete generalization was found in the low‐TD (1.0 mg/kg) group. Experiment 2 was designed to assess whether the MS‐AMPH mixture resulted in the creation of a functionally new stimulus. With a three‐choice drug‐discrimination procedure, two new groups were trained to discriminate between 3.2 mg/kg MS, SAL, and 1.8 mg/kg AMPH. Once training criteria were met, subjects were divided into two groups and one group's MS training dose was faded up to 10 mg/kg. Data clearly indicated that MS‐AMPH combinations did not produce novel stimuli. Experiment 3 was designed to assess the MS‐AMPH combinations in a three‐choice quantitative discrimination using 1.8 mg/kg MS vs. SAL vs. 10 mg/kg MS as discriminative stimuli. Data suggested that if masking does occur, it is a result of shifting the dose‐response function to the left (i.e., to a nondiscriminable dose). We conclude that perceptual masking of drug stimuli can occur, but the phenomenon seems dependent on training dose and/or drug and behavioral history.

Factors affecting conditional discrimination learning by pigeons: II. Physical and temporal characteristics of stimuli

Four experiments were performed to determine the stimulus characteristics that favor the development of conditional stimulus control in the single reversal paradigm with pigeon subjects. In Experiment 1, pigeons were trained on a successive discrimination between tone frequencies ranging from 350 to 3500 Hz in a particular houselight context condition (houselight-on or -off). The subjects then were trained on the reversal of the tone discrimination in the alternative context. Subsequent tone-frequency generalization testing in the two contexts indicated that they had failed to gain conditional control over the pigeons’ discriminative performance. Such control was obtained in Experiment 2, in which the two problems were alternated daily for 32 sessions of training. The gradients then peaked at the appropriate S+ value in each context. In Experiment 3, the key colors (blue vs. red) served as contexts while pigeons learned a successive discrimination in which the discriminative cues were houselight-on versus houselight-off conditions. This was followed by a reversal of the discrimination in the alternative key-color context condition. The key colors were effective conditional cues in this situation. In a previous experiment (Thomas, McKelvie, & Mah, 1985), key color had been ineffective as a conditional cue when the discriminative cues were lines superimposed on the colored background. In Experiment 4, key color was effective when the color and lines were presented on a single key as in the earlier experiment, but were sequenced such that the onset of the key color preceded and then overlapped the presentation of the lines. We concluded that conditional discriminations are easiest for pigeons when visual cues are used, but the conditional and discriminative cues must be presented in such a way that they do not combine to form a psychological compound.

Two perceptual variables in within-event learning

Four autoshaping experiments employed pigeon subjects to explore within-stimulus learning. Experiments 1 and 2 investigated the formation of an association between two elements within a visual compound as a function of the similarity of the elements to each other. As in earlier experiments on the formation of associations between stimuli, similarity improved learning within a stimulus. Experiments 3 and 4 examined the formation of color-form associations when the color was a property of the form or of the ground on which the form occurred. Learning was better between the form and its color than between the form and the color of its background. These results suggest that perceptual variables contribute to within-stimulus learning.

Effects of peripherally injected pituitary peptides on recognition memory in pigeons

The effects of peripheral injection of arginine vasopressin (AVP), oxytocin (OT), arginine vasotocin (AVT), adrenocorticotrophic hormone (ACTH 4–10) and α-melanocyte-stimulating hormone (α-MSH) were studied, using pigeon subjects and a pair comparison task, with and without intervening delays between stimuli presentation. The highest dose (20 μg/kg) of AVT impaired performance by disrupting input, but not storage. General cognitive ability was unimpaired, as were perceptual mechanisms. None of the other peptides affected recognition memory, in that forgetting curves were unchanged when compared with control. The results are discussed in terms of species-specific roles for these peptides.

Changeover cost and switching between concurrent adjusting schedules

Using pigeon subjects we studied the effects of changeover cost on rates of switching between concurrent adjusting variable ratio schedules. Each side-key schedule while activated increased with the delivery of each reinforcer and decreased with reinforcer delivery when the alternate key was active. With no changeover cost, changeovers were frequent although not optimal. Switching from one side-key to the other was reduced following the addition of a single center-key changeover response, and reduced progressively further with increasing time (FI;FT), or response (FR;VR) requirements. This procedure is discussed as a model for the determination of variables which control a forager's giving-up in one food source patch and switching to another.

The Effect of Intertrial Conditioned Stimuli in Autoshaping

Three autoshaping experiments, using pigeon subjects, examined the effect of presenting an S+ or an S− on acquisition to a different conditioned stimulus (CS). Experiment 1 found that signalling intertrial food with an S+ or an S− allowed acquisition of responding to the target-CS; however, that acquisition was slower when the signal was the S+. Experiment 2 found that even when the S+ or S− were presented without food in the intertrial interval, acquisition was slower in the group receiving the S+. Experiment 3 found that a similar, but weaker effect occurred when the S+ or S− stimuli were presented in the session prior to target-CS training, rather than intermixed. These results have implications for the interpretation of experiments that use a signalling manipulation to assess the interaction of CS and context in Pavlovian conditioning; they suggest that signalling unconditioned stimuli (USs) may have consequences other than that of modulating context-US learning.

Effect of separate presentation of the elements on within-compound learning in autoshaping

Five experiments used an autoshaping procedure with pigeon subjects to explore the consequences of separate-element presentation for within-compound associations. When a keylight compound had initially been reinforced, separate presentation of one element reduced responding to the other. This was true whether that separate-element presentation was itself reinforced or nonreinforced. That suggests that the detrimental effect of separate-element presentation results from an effect on the within-compound association, rather than one on the association of either element with the US. When the compound had initially been nonreinforced, a moderate level of reinforcement of one element resulted in responding to the other element. However, more extensive reinforcement reduced that responding. Moreover, an attempt to reverse the adverse consequences of extensive separate-element presentation by further exposure to the compound was not successful. These results comment on the associative mechanisms underlying performance in sensory preconditioning and related paradigms.

Sequential processes in the generalization and transfer of stimulus control

Prior research indicated that a training sequence consisting of a negative stimulus followed by a positive stimulus constitutes the minimal condition for the production of postdiscrimination phenomena typically observed after training with random sequences of the discriminanda. The present experiments, employing multiple schedules with pigeon subjects, confirmed the earlier findings but indicated that they are restricted to procedures in which the reinforcing stimulus may acquire a discriminative function that competes with the control exerted by the nominal discriminanda. The sequences in which the discriminanda were presented did not differentially affect subsequent measures of generalization and transfer if the discriminative function of reinforcement were degraded either by introducing some reinforcers during the negative stimulus (Experiment 1) or by omitting some reinforcers during the positive stimulus (Experiment 2). It was concluded that the sequence in which the discriminanda are presented during discrimination training does not contribute fundamentally to the processes responsible for discrimination formation with random training sequences.

Effect of a stimulus intervening between CS and US in autoshaping.

Five experiments explored the effect of placing a stimulus between the termination of a key light CS and the onset of a food US in an autoshaping preparation with pigeon subjects. Whether that stimulus was itself a key light evoking pecking or an auditory event failing to evoke pecking, it facilitated performance to the key light CS. The use of a within-subjects design made differential conditioning of background cues and stimulus generalization unlikely accounts. Experiment 3 found that extinction of the intervening stimulus did not remove the facilitative effect. Experiment 4 found that pairing the CS with food and the intervening stimulus did not produce the effect unless both occurred on the same trial. Together, these experiments rule out an account in terms of second-order conditioning of the CS by the intervening stimulus. Experiment 5 used an intervening stimulus in a second-order conditioning design to demonstrate that the stimulus acted to improve the association between the CS and the reinforcer. That experiment found the intervening stimulus to make responding to the CS more vulnerable to subsequent extinction of its reinforcer. Together, these experiments document a kind of catalytic effect of the intervening stimulus on the CS-reinforcer association.

The local organization of behavior: discrimination of and memory for simple behavioral patterns.

A procedure was developed to enable nonverbal organisms to report what they remember of the temporal organization of their recent behavior. A baseline behavior with known temporal structure was established by a concurrent variable-interval variable-interval schedule for two temporal patterns of behavior (two different classes of reinforced inter-response times). The five pigeon subjects emitted these two temporal patterns on a center key and were occasionally given a short-term memory probe for their most-recently-emitted pattern. The probes consisted of symbolic delayed matching-to-sample tests, in which a response on a green side key was reinforced if the most recent pattern belonged to the shorter reinforced class, and a response to a red side key was reinforced if the most recent pattern belonged to the longer reinforced class. All subjects could report with over ninety percent accuracy what their most recently emitted behavioral pattern was when a retention interval separating the pattern from the memory probe was only .1 seconds. The retention interval was then manipulated, and it was found that recall for a pattern was frequently above chance after a delay of as much as eight seconds. Thus, pigeons can remember their most recent interresponse time not only right after it is emitted, but for several seconds thereafter. In other conditions, the patterns themselves were manipulated. It was found that as the patterns became more similar, discrimination became poorer. These results agree with the view that reinforcement tends to organize and integrate the local structure of behavior to the extent to which that structure is remembered.