Do pigeons (Columba livia) study for a test?

In 4 experiments, the authors asked whether pigeons (Columba livia) would show metamemory by choosing to study a sample stimulus before taking a memory test. In Experiments 1a–1c, pigeons chose between cues that led either to exposure to a sample stimulus or directly to the comparison test stimuli without seeing the sample in a delayed matching-to-sample task. The same choice was used in Experiment 2 to see whether pigeons would take a reminder when memory of the sample was weak. In Experiments 3 and 4, pigeons’ responses led to either a choice between red and green side keys with a sample present to guide the choice or a choice with no sample present. The findings of all of these experiments suggest the absence of metamemory in pigeons. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Timing in Choice Experiments.

In Experiment 1, pigeons chose between variable- and fixed-interval schedules. The timer for 1 schedule was reset by a reinforcement on that schedule or on either schedule. In both cases, the pigeons timed reinforcement on each schedule from trial onset. The data further suggest that their behavior reflects 2 independent processes: 1 deciding when a response should be emitted and responsible for the timing of the overall activity, and the other determining what this response should be and responsible for the allocation of behavior between the 2 response keys. Results from Experiment 2, which studied choice between 2 fixed-interval schedules, support those 2 conclusions. These results have implications for the study of operant choice in general. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Context specificity of implicit preferences: The case of human preference for red.

Three experiments were conducted on color preference using a spontaneous selection paradigm with infant participants. Experiment 1 demonstrated that participants prefer red over green in a friendly laboratory environment. Experiment 2 demonstrated that participants’ preference for red varies with the context in which the color is presented: Red is preferred in a hospitable context (following a happy face), but not in a hostile context (following an angry face). The opposite pattern was found for the control color green. Experiment 3 used the same context manipulation, but a second control color, gray, was added to clearly examine whether context affects preference for red only. As predicted, given a second alternative choice, context-dependent preference for red, but not green or gray, was found. These results represent the first evidence of context moderation in the color preference literature. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exploring a Concurrent-Chains Paradox: Decreasing Preference as an Initial Link Is Shortened.

Experiments with pigeons and rats on concurrent-chains schedules examined a paradoxical effect reported by R. A. Preston and E. Fantino (1991). One schedule in the concurrent chain had a variable-interval (VI) 60-s initial link, and its terminal link was a 10-s delay to food. The other schedule had an initial link that ranged from VI 60 s to VI 2 s, and its terminal link was a 20-s delay to food. The paradoxical effect--a decrease in preference for the 20-s delay as its initial link was shortened--was found in some conditions but not in others. An analysis of response-reinforcer delays suggested that the paradoxical effect occurred in conditions in which responding on the short VI schedule almost always led to the 20-s delay, eliminating the possibility of switching to the alternative with the shorter delay. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Superordinate categorization via learned stimulus equivalence: Quantity of reinforcement, hedonic value, and the nature of the mediator.

Three experiments examined superordinate categorization via stimulus equivalence training in pigeons. Experiment 1 established superordinate categories by association with a common number of food pellet reinforcers, plus it established generalization to novel photographic stimuli. Experiment 2 documented generalization of choice responding from stimuli signaling different numbers of food pellets to stimuli signaling different delays to food reinforcement. Experiment 3 indicated that different numbers of food pellets did not substitute as discriminative stimuli for the photographic stimuli with which the food pellets had been paired. The collective results suggest that the effective mediator of superordinate categories that are established via learned stimulus equivalence is not likely to be an accurate representation of the reinforcer, neither is it likely to be a distinctive response that is made to the discriminative stimulus. Motivational or emotional mediation is a more likely account. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pigeons prefer conditional stimuli over their absence: A comment on Roberts et al. (2009).

Recently, Roberts et al. (2009) have suggested that pigeons performing delayed matching-to-sample appear unwilling to request to see the sample again (or even for the first time) prior to choice, even if that choice would result in an increase in matching accuracy. In each of their four experiments, however, presentation (Experiments 3 & 4) or representation of the sample (Experiments 1 & 2) resulted in an added delay to reinforcement. Thus, the pigeons had to choose between an immediate reinforcer on about 50% of the trials and a delayed reinforcer on a significantly higher percentage of the trials. In the present research, when we equated the two alternatives for delay to reinforcement, we found that pigeons generally showed a significant preference for trials with a relevant sample over trials with an irrelevant sample. When the contingencies were reversed, most of the pigeons reversed their preference. Although these results do not present evidence for metacognition, they do show that pigeons are sensitive to the potential for a higher probability of reinforcement when delay to reinforcement is controlled. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Further analysis of perception of the standard Müller-Lyer figures in pigeons (Columba livia) and humans (Homo sapiens): Effects of length of brackets.

Nakamura, Fujita, Ushitani, & Miyata (2006) have shown that pigeons perceive the standard Müller-Lyer illusion. In this report, the authors examined effects of bracket sizes on perception of this illusion in pigeons (Columba livia) and humans (Homo sapiens). In Experiment 1, three pigeons were retrained to classify six lengths of target lines into “long” and “short” by pecking two keys on the monitor, ignoring the two brackets oriented toward the same direction. In the tests that followed, the standard Müller-Lyer figures of different bracket sizes were presented. All birds chose “long” more frequently for the figures having inward-pointing brackets (>), regardless of bracket sizes. The overestimation of the target lines of inward-pointing figures continued to increase in pigeons, whereas it decreased as the bracket size became longer in humans (Experiment 2). The results suggest that these two species perceive the standard Müller-Lyer illusion with long brackets in different ways. Perhaps pigeons might not perceive illusions induced by contrast with the surrounding stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perception of the standard and the reversed Müller-Lyer figures in pigeons (Columba livia) and humans (Homo sapiens).

The authors compared perception of the standard and reversed Müller-Lyer figures between pigeons (Columbia livia) and humans (Homo sapiens). In Experiment 1, pigeons learned to classify 6 lengths of target lines into "long" and "short" categories by pecking 2 keys on the monitor, ignoring the 2 brackets so placed that they would not induce an illusion. In the test that followed, all 3 birds chose the "long" key more frequently for the standard Müller-Lyer figures with inward-pointing brackets (>). The subjects' responses were accountable by neither overall lengths of the figures nor horizontal gaps between the 2 brackets. For the reversed figures, effects of the brackets were absent. These results suggested that the pigeons perceived the standard Müller-Lyer illusion but not the reversed one. Experiment 2 confirmed that humans perceived both types of the illusion. Pigeons and humans may perceive the same illusory figures in different ways. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inferior-good and Giffen-good effects in monkey choice behavior.

In Experiment 1, two monkeys chose on a trials basis between a large, bitter pellet and a small, standard pellet in 1-hr sessions. During low-income conditions, produced by having a 60-s or 70-s intertrial interval, the large, bitter pellet was generally preferred. This preference reversed during the high-income conditions, which were produced by reducing the intertrial interval to 15 s. The drop in consumption of large, bitter pellets as income increased defines this food as an inferior good. In Experiment 2, the high-income choice procedure was altered by making pellet delivery probabilistic. When the price of the bitter-tasting pellet was increased by decreasing its probability of delivery, both monkeys chose more of it, measured either by choices or by pellets delivered; when the price of the bitter pellet was decreased, monkeys chose less of it. These results fulfill the conditions for what economists call a Giffen good. Although the results of Experiments 1 and 2 cannot be explained in terms of most psychological accounts of choice, they are interpretable in terms of economics. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Molar function depends on molecular structure of behavior.

Pigeons chose between green side keys, then waited a shorter or longer time before pecking a center key, and finally chose between red side keys. Two successive left choices (to green and then red) with a shorter wait intervening, or 2 successive right choices with a longer wait intervening, were intermittently reinforced with food. The 2 required waiting times and the relative frequency of reinforcement for the shorter reinforced pattern were varied. Molar preference, defined in terms of coherent responses that satisfied the molecular reinforcement contingency, conformed to the highly adaptive matching level, but molar preference, defined in terms of incoherent responses, did not. The molar matching result therefore generalizes to responses with complex molecular structures provided that analyses distinguish between coherent and incoherent responses. The results are compatible with the idea that awareness can facilitate adaptation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Summation of symbols by pigeons (Columba livia): The importance of number and mass of reward items.

In each of 3 experiments, different sets of 4 pigeons (Columba livia) were trained to discriminate between 2 visual symbols that covered wells containing food items that varied in number, mass, or both. In Experiment 1, the symbols were associated with 0, 1, 3, 5, 7, or 9 pieces of grain reward. The pigeons learned to choose the symbol corresponding to the larger reward, and on summation tests, they chose the pair of symbols that summed to the larger total reward. When number of food pellets was varied but mass of reward was held constant in Experiment 2, preference for the larger number symbols failed to appear. When number was held constant and mass was varied in Experiment 3, the pigeons showed a clear preference for the larger mass symbols on single-symbol and summation tests. These findings show that pigeons summate the value of symbols and are more likely to represent symbols by mass of food reward than by number of food items. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influences of delay and rate of reinforcement on discrete-trial choice.

An adjusting procedure was used to measure 4 White Carneaux pigeons' preferences among alternatives that differed in the duration of a delay before reinforcement and of an intertrial interval (ITI) after reinforcement. In most conditions, a peck at a red key led to a fixed delay, followed by reinforcement, a fixed ITI, and then the beginning of the next trial. A peck at a green key led to an adjustable delay, reinforcement, and then the next trial began without an ITI. The purpose of the adjusting delay was to estimate an indifference point, or a delay that made an S approximately indifferent between the 2 alternatives. As the ITI for the red key increased from 0 to 60 sec, the green-key delay at the indifference point increased systematically, but only slightly. The fact that there was some increase showed that Ss' choices were controlled by more than simply the delay to the next reinforcer. An analysis that ignored reinforcement rate but that considered the delays between a choice response and the reinforcers on subsequent trials was able to account for most of the obtained increases in green-key delays. It is concluded that in this type of discrete-trial situation, rate of reinforcement exerts little or no control over choice behavior. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Control of Matching by Differential Outcome Expectancies in the Absence of Differential Sample-Outcome Associations: A serial compound view.

In this study, pigeons learned 2 separate one-to-many conditional discriminations in which they matched form samples to line and hue comparisons. Correct choices within each comparison dimension yielded differential (food vs. no-food) outcomes that were not predictable from the samples alone. At asymptote, latency to make a correct choice was shorter when food was the contingent outcome than when no food was the outcome. More important, when the samples from each task were subsequently exchanged, comparison choice varied systematically as a function of the sample and the set of new comparison alternatives that followed them. Together, these results indicate that choices were cued by differential outcome expectancies arising from serial compounds consisting of each sample and the dimensional characteristics of the comparisons. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Scalar expectancy theory and choice between delayed rewards.

In this article scalar expectancy theory is applied to variable and fixed delays to reward. It is assumed that all delays are represented in memory with scalar variance and that subjects choose between alternatives by sampling from the memory distributions associated with each and choosing the smaller delay. This simple scheme is shown to entail four common findings in the choice literature: (a) approximate matching of choice ratios to reward ratios (the matching law) when both alternatives are associated with variable delays scheduled with constant probability; (b) undermatching, in which choice is closer to indifference than matching, when both alternatives are variable but scheduled with uniform distributions; (c) overmatching, in which choice is more extreme than matching, when both alternatives are fixed delays; and (d) preference for variable delays scheduled with a constant probability over fixed delays. Overmatching and Weber's law are illustrated in experiments using the time-left procedure (Gibbon & Church, 1981). The preference for variable delay is demonstrated in this procedure, followed by study of a unique variable schedule of delays for which the theoretical account predicts, and the data confirm, the elimination of the preference for variability. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pigeons (Columba livia) associate time intervals with symbols in a touch screen task: Evidence for ordinality but not summation.

The present experiments examined whether pigeons can sum symbols that are associated with various temporal consequences in a touch screen apparatus. Pigeons were trained to discriminate between two visual symbols that were associated with 0, 1, 2, 3, 4, or 5 s either of delay to 4 s of hopper access (delay group) or duration of hopper access (reward group). In Experiment 1, the pigeons in both groups learned to select the symbol associated with the more favorable outcome, and they successfully transferred this discrimination to novel symbol pairs. However, when tested with 2 pairs of symbols associated with different summed durations, they responded on the basis of a simple response rule rather than the sum of the symbol pair. In Experiment 2, the reward group was presented with four symbols at once and was allowed to successively choose one symbol at a time. All pigeons chose the symbols in order from largest to smallest. This indicates that pigeons formed an ordered representation of symbols associated with different time intervals, even though they did not sum the symbols. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learned avoidance of flavors signaling reduction in a nutrient.

Food-deprived rats learned to avoid a flavor negatively correlated with access to a rich nutrient, 20% maltodextrin (20M) solution. This avoidance in two-bottle choice tests was produced by training consisting of either an unpaired condition where sessions of unflavored 20M were intermixed with sessions of 2 or 3% maltodextrin (2M or 3M) flavored with salt (Experiment 1) or almond (Experiments 3 and 4) or a differential conditioning procedure where one flavor was mixed with 20M and another with 2M (Experiment 2). Avoidance was counter-conditioned by mixing the target flavor with 20M (Experiment 1), generalized to a neutral context (Experiment 3), and displayed strong resistance to extinction (Experiment 4). The results demonstrated that food avoidance learning can occur in the absence of an aversive unconditioned stimulus and indicated that unpaired control groups and differential conditioning procedures may be misleading in flavor preference learning research when further control conditions are absent. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Finding hidden food: Behavior on visible displacement tasks by mynahs (Gracula religiosa) and pigeons (Columba livia).

Four visible displacement tasks showed that pigeons can learn to find hidden food but revealed little evidence of spontaneous retrieval. In Experiment 1, given a choice between 2 screens, 1 of which concealed food, pigeons performed at chance level. In Experiment 2, when shown a moving cart of grain that disappeared into a tunnel and reemerged, they spontaneously followed the cart if the tunnel was clear but not if it was opaque. After learning to follow the cart, they would follow it when it was filled with grit. In Experiment 3, pigeons were rewarded for pecking at a key when a horizontally moving figure disappeared behind an occluder. Performance was characterized by a time-waiting rule. Experiment 4 describes a species comparison in finding food hidden in 1 of 4 compartments: As predicted from ecological considerations, mynahs performed better than pigeons. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory strategies in pigeons' performance of a radial-arm-maze analog task.

Pigeons were presented with an analog of a radial-arm-maze task involving 5 response keys. In Experiment 1, pigeons were exposed to either a linear (L) or a two-dimensional matrix (M) array of the 5 keys, and the keys were either each of a distinctive hue (H) or were all white (W). Acquisition was facilitated both by M and by H. In Experiment 2, increasing the number of pecks that constituted a choice from 5 to 20 for half of the LW birds had little effect on performance. In Experiment 3, a delay was interpolated after a number of choices that varied across trials. All groups except the LW 5-peck group showed little disruption in performance with increasing delay (up to a maximum of 1 hr). Inverted-U-shaped point-of-delay interpolation functions were found for each group. The data suggest that pigeons retrospectively coded choices already made when the delay occurred early in the trial and prospectively coded choices yet to be made when the delay occurred late in the trial. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Context effects on choice

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.     

Mechanisms underlying the effects of unsignaled delayed reinforcement on key pecking of pigeons under variable-interval schedules

Three experiments were conducted to test an interpretation of the response-rate-reducing effects of unsignaled nonresetting delays to reinforcement in pigeons. According to this interpretation, rates of key pecking decrease under these conditions because key pecks alternate with hopper-observing behavior. In Experiment 1, 4 pigeons pecked a food key that raised the hopper provided that pecks on a different variable-interval-schedule key met the requirements of a variable-interval 60-s schedule. The stimuli associated with the availability of the hopper (i.e., houselight and keylight off, food key illuminated, feedback following food-key pecks) were gradually removed across phases while the dependent relation between hopper availability and variable-interval-schedule key pecks was maintained. Rates of pecking the variable-interval-schedule key decreased to low levels and rates of food-key pecks increased when variable-interval-schedule key pecks did not produce hopper-correlated stimuli. In Experiment 2, pigeons initially pecked a single key under a variable-interval 60-s schedule. Then the dependent relation between hopper presentation and key pecks was eliminated by arranging a variable-time 60-s schedule. When rates of pecking had decreased to low levels, conditions were changed so that pecks during the final 5 s of each interval changed the keylight color from green to amber. When pecking produced these hopper-correlated stimuli, pecking occurred at high rates, despite the absence of a peck-food dependency. When peck-produced changes in keylight color were uncorrelated with food, rates of pecking fell to low levels. In Experiment 3, details (obtained delays, interresponse-time distributions, eating times) of the transition from high to low response rates produced by the introduction of a 3-s unsignaled delay were tracked from session to session in 3 pigeons that had been initially trained to peck under a conventional variable-interval 60-s schedule. Decreases in response rates soon after the transition to delayed reinforcement were accompanied by decreases in eating times and alterations in interresponse-time distributions. As response rates decreased and became stable, eating times increased and their variability decreased. These findings support an interpretation of the effects of delayed reinforcement that emphasizes the importance of hopper-observing behavior.