Pigeons can discriminate “good” and “bad” paintings by children

Humans have the unique ability to create art, but non-human animals may be able to discriminate “good” art from “bad” art. In this study, I investigated whether pigeons could be trained to discriminate between paintings that had been judged by humans as either “bad” or “good”. To do this, adult human observers first classified several children’s paintings as either “good” (beautiful) or “bad” (ugly). Using operant conditioning procedures, pigeons were then reinforced for pecking at “good” paintings. After the pigeons learned the discrimination task, they were presented with novel pictures of both “good” and “bad” children’s paintings to test whether they had successfully learned to discriminate between these two stimulus categories. The results showed that pigeons could discriminate novel “good” and “bad” paintings. Then, to determine which cues the subjects used for the discrimination, I conducted tests of the stimuli when the paintings were of reduced size or grayscale. In addition, I tested their ability to discriminate when the painting stimuli were mosaic and partial occluded. The pigeons maintained discrimination performance when the paintings were reduced in size. However, discrimination performance decreased when stimuli were presented as grayscale images or when a mosaic effect was applied to the original stimuli in order to disrupt spatial frequency. Thus, the pigeons used both color and pattern cues for their discrimination. The partial occlusion did not disrupt the discriminative behavior suggesting that the pigeons did not attend to particular parts, namely upper, lower, left or right half, of the paintings. These results suggest that the pigeons are capable of learning the concept of a stimulus class that humans name “good” pictures. The second experiment showed that pigeons learned to discriminate watercolor paintings from pastel paintings. The subjects showed generalization to novel paintings. Then, as the first experiment, size reduction test, grayscale test, mosaic processing test and partial occlusion test were carried out. The results suggest that the pigeons used both color and pattern cues for the discrimination and show that non-human animals, such as pigeons, can be trained to discriminate abstract visual stimuli, such as pictures and may also have the ability to learn the concept of “beauty” as defined by humans.     

Pigeons learn stimulus identity and stimulus relations when both serve as redundant,relevant cues during same-different discrimination training

The authors taught pigeons to discriminate displays of 16 identical items from displays of 16 nonidentical items. Unlike most same-different discrimination studies--where only stimulus relations could serve a discriminative function--both the identity of the items and the relations among the items were discriminative features of the displays. The pigeons learned about both stimulus identity and stimulus relations when these 2 sources of information served as redundant, relevant cues. In tests of associative competition, identity cues exerted greater stimulus control than relational cues. These results suggest that the pigeon can respond to both specific stimuli and general relations in the environment.     

Conditional discrimination with ambiguous stimuli.

Five pigeons learned a two-key conditional discrimination. When background color on both keys was red, pecks on the key with a horizontal line produced food. When the color was green, pecks on the key with a vertical line produced food. During part of the experiment, color was presented on only one of the keys. It was found that accuracy was higher when color was combined with the line stimulus correlated with nonreinforcement. In another part of the experiment, color was presented on both keys but a line was present only on one. Accuracy was higher when the line accompanied the nonreinforced option than when the line accompanied the reinforced option. Superior performance when the combined stimuli were displayed on the nonfood key may be explained by the association of different components of the compound stimuli with reinforcement or as the result of rules pigeons follow in solving conditional discriminations.     

Do birds (pigeons and bantams) know how confident they are of their perceptual decisions?

Rhesus monkeys are known to recognize confidence about their immediate perceptual and cognitive decisions by using a betting procedure (Son and Kornell in The missing link in cognition: origins of self-reflective consciousness. Oxford University Press, New York, pp 296–320, 2005; Kornell et al. in Psychol Sci 18:64–71, 2007). In this report, we examined whether this ability is shared in two avian species (pigeons and bantams) in order to know how widespread this metacognitive ability is among animals. We trained pigeons and bantams to search for a differently colored disk (target) among others (distracters) displayed on a touch-sensitive monitor. In test, the subjects were required to choose one of two confidence icons, “risk” and “safe”, after the visual search. A peck at the “risk” icon after a correct response in the visual search (i.e., a peck at the target) was reinforced by food and light, while that after an incorrect response (i.e., a peck at a distracter) resulted in a timeout. A peck at the “safe” icon was always reinforced by food and light, or by light only, regardless of the visual search result. The percentages of “safe” choices after incorrect responses were higher than after correct responses in all six pigeons and two of three bantams. This behavior generalized to novel stimuli in some subjects, and even to a novel line-classification task in a pigeon. These results suggest that these two distantly related avian species have in common a metacognitive ability that allows them to recognize confidence about their immediate perceptual decisions.     

Stimulus effects on concurrent performance in transition

Six experimentally naive pigeons were exposed to concurrent variable-interval variable-interval schedules in a three-key procedure in which food reinforcement followed pecks on the side keys and pecks on the center key served as changeover responses. In Phase 1, 3 birds were exposed to 20 combinations of five variable-interval values, with each variable-interval value consistently associated with a different color on the side keys. Another 3 pigeons were exposed to the same 20 conditions, but with a more standard procedure that used a nondifferential discriminative stimulus on the two side keys throughout all conditions. In Phase 2, the differential and nondifferential stimulus conditions were reversed for each pigeon. Each condition lasted for one 5-hr session and one subsequent 1-hr session. In the last 14 conditions of each phase, the presence of differential discriminative stimuli decreased the time necessary for differential responding to develop and increased the sensitivity of behavior to reinforcement distribution in the 1st hr of training; during the last hours of training in each condition, however, the effects of the differential discriminative stimuli could not be distinguished from the effects of reinforcement distribution per se. These results show the importance of studying transitions in behavior as well as final performance. They may also be relevant to discrepancies in the results of previous experiments that have used nonhuman and human subjects.     

Patterns of covert speech behavior and phonetic coding

In previous research a discriminative relationship has been established between patterns of covert speech behavior and the phonemic system when processing continuous linguistic material. The goal of the present research was to be more analytic and pinpoint covert neuromuscular speech patterns when one processes specific instances of phonemes. Electromyographic (EMG) recording indicated that the lips are significantly active when visually processing the letter “P” (an instance of bilabial material), but not when processing the letter “T” or a nonlinguistic control (C) stimulus. Similarly, the tongue is significantly active when processing the letter “T” (an instance of lingual-alveolar material), but not when processing the letters “P” or “C.” It is concluded that the speech musculature covertly responds systematically as a function of class of phoneme being processed. These results accord with our model that semantic processing (“understanding”) occurs when the speech (and other) musculature interacts with linguistic regions of the brain. In the interactions phonetic coding is generated and transmitted through neuromuscular circuits that have cybernetic characteristics.     

Transfer of directed-forgetting cues across discrimination tasks with pigeons

Directed forgetting is shown as impaired performance on a memory test following an instruction that the presented items will not be tested. Experiments utilizing the delayed matching-to-sample (DMTS) task have demonstrated that this ability to actively control memory is present in animals; however, no study has yet confirmed that cues to forget established in one DMTS discrimination will successfully transfer to other discriminations. Lacking such evidence, it is not clear whether forgetting cues act as “higher level” task instructions or are represented more simply, perhaps as part of a sample-specific sequence of events. The present study revealed good transfer of the forget cue function in pigeons after prior training with the forget cues in a separate discrimination. This finding is discussed in relation to analogous experiments on occasion setting, in which training within more than one discriminative context has been shown to be critical to the transfer of a conditional relation.     

Responses and pauses: discrimination and a choice catastrophe.

Pigeons produced a stimulus change either by responding or by not responding for a specified time period (by pausing). They then had to choose between two responses to obtain food. One choice was correct if the first component had been completed by a response; the other was correct if the component had been completed by a pause. The pigeons usually chose correctly, thereby indicating that they used their own prior behavior as a discriminative stimulus. Fixed pause requirements did not produce equal first component completions by a response and by a pause. To obtain equality, the pause requirement was titrated as a function of current performance. Titration resulted in equal completions and also produced accurate discrimination. In addition to showing that pigeons discriminated whether they had responded or paused, the data displayed and discontinuous functions predicted by catastrophe theory. Another procedure used forced choice rather than titration to produce equal completions by pausing and responding and also showed accurate discrimination of behavior.     

Conditional choice-unique outcomes establish expectancies that mediate choice behavior

Conditional discriminative choice tasks can be arranged such that all correct choices yield the same reinforcer or such that each type of correct choice has its own unique reinforcer. The former is the traditional “Common Outcomes” Procedure; the latter is the “Differential Outcomes” Procedure. Use of this Differential Outcomes Procedure facilitates the rate of learning, increases the asymptotic level of performance, and enhances working-memory based performances in both animals and humans. These facts have stimulated many questions and experiments about learning and memory mechanisms and fostered potential applications. This paper is based upon presentations at the Pavlovian Society Annual Meeting, Annapolis, MD, September 2000.     

Average uncertainty as a determinant of observing behavior

After discrimination training on a multiple variable-interval extinction schedule of food reinforcement, pigeons were placed on the uncued or mixed version of the same schedule and allowed to make an optional “observing response” that converted the uncued schedule to the corresponding cued schedule by providing a 20-sec exposure to the appropriate discriminative stimulus. The schedule consisted of one hundred 40-sec components, and the probability that any one of them would be a variable-interval component was systematically varied between 0.00 and 1.00. The results showed that the amount of observing behavior was an inverted “U” function of the probability of the variable-interval component. Few observing responses occurred at probabilities of 0.00 or 1.00, and maximum responding occurred at a value less than 0.50.     

Learning and transfer of relational matching-to-sample by pigeons

We trained pigeons on a relational matching-to-sample task to see whether a nonprimate species can discriminate higher-order “relations between relations.” We required the birds to relationally match arrays of 16 items that were chosen from five nonoverlapping sets of 20 colored computer icons. On each trial, randomly selected icons from one set were placed into a 4×4 grid to form a sample; onsame trials, all 16 icons were identical to each other, whereas ondifferent trials, all 16 icons were different from each other. After 10-20 pecks, 16-itemsame anddifferent testing arrays were presented that were created from an entirely different icon set. Because no icons were common to the sample and testing arrays, discriminating higher-order relations was required for success on the tests. As have primates in similar tasks, pigeons successfully learned and transferred this relational discrimination, suggesting that both birds and mammals possess the cognitive antecedents of analogical reasoning.     

Discrimination of painting style and quality: pigeons use different strategies for different tasks

Birds have visual cognition as well developed as humans. Sometimes, the birds show visual discrimination similar to humans, but the birds may use different cues. Previous reports suggest that global configuration cues are salient for humans, whereas local elemental cues are salient for pigeons. I analyzed the discriminative behavior of pigeons with scrambled images because scrambled images keep the local elemental cues of the original images but lose the global configuration cues. If pigeons use local elemental cues, then, they should show transfer of discrimination from the original images to their scrambled images and also transfer from the scrambled images to their original images. In Experiment I, I trained pigeons on painting style discrimination (Japanese paintings vs. Western impressionist paintings) using either the original or scrambled images and found that the pigeons showed bidirectional transfer. In Experiment II, I trained pigeons on discrimination of “good” versus “bad” paintings using children’s paintings. The birds showed poor transfer from the original images to their scrambled images and vise versa. Thus, the pigeons discriminated good and bad paintings based mostly on global configuration cues in this case. These results suggest that the pigeons use different cues for different discriminations.     

Induced attack during multiple fixed-ratio, variable-ratio schedules of reinforcement

Two pigeons were exposed to a multiple schedule of reinforcement: in the presence of one discriminative stimulus, key pecks produced grain according to a fixed-ratio schedule; in the presence of a second discriminative stimulus, key pecks produced grain according to a variable-ratio schedule. The key-peck requirements in the two components were increased in successive stages from 50 to 125 responses. Live target pigeons were restrained at the rear of the chamber. Attacks against the targets were automatically recorded, and a variety of measures of attack behavior were taken. Attacks, when they occurred, always followed grain presentation. All measures revealed higher levels of attack during the fixed-ratio component at all parameter values. All measures generally increased with increases in fixed-ratio values with both birds, and with increases in variable-ratio values with one bird. With the other bird, only the per cent of reinforcements followed by attack increased with increases in variable-ratio value; all other measures first increased and then decreased. Both increasing and bitonic functions relating induced attack to schedule parameters have been reported in experiments usually employing a single measure of attack. The measures have varied widely among these experiments. It is suggested that further studies of induced attack examine a wider range of schedule parameters and that relationships among measures be studied.     

Separating the effects of salience and disparity on the rate of observing

Pigeons producing deliveries of grain on a mixed variable-interval, extinction schedule by pecking a center key could also produce discriminative stimuli on concurrent variable-interval schedules by pecking the left or right observing key. The stimuli produced by each observing key were varied independently. In the first experiment, the negative discriminative stimulus was at the far end of the spectrum from the key illumination accompanying the mixed schedule and from the positive discriminative stimulus. When the magnitude of the difference between the latter two stimuli (salience) was varied, more pecks occurred on the observing key producing the larger of the two differences than on the key producing the smaller difference. In the second experiment, the stimulus accompanying the mixed schedule was at the far end of the spectrum, and the magnitude of the difference between the two discriminative stimuli (disparity) was varied. The proportion of pecks occurring on each observing key shifted systematically in the direction of the key producing the larger difference. The salience of the discriminative stimuli and their disparity each has an independent influence on the frequency of observing when the other is controlled, but the effect of the salience appears to be the more substantial.     

The relationship between observing behavior and food-key response rates under mixed and multiple schedules of reinforcement

Pigeons were trained under an observing response procedure in which pecks on one key (food key) were reinforced under a mixed fixed-interval 30-sec extinction schedule. A response on a second (observing) key replaced the mixed-schedule stimulus with either of two multiple-schedule stimuli (red and green keylights) for 5 sec. Observing response rates were positively correlated with food-key response rates in the presence of multiple-schedule stimuli and inversely related to food-key response rates in the presence of mixed-schedule stimuli. These results suggest that observing response output is controlled not only by the stimuli produced by observing responses but also by the stimuli in the presence of which observing responses occur. The possibility that observing responses alter the probability of reinforcement is advanced.     

Pigeons' preferences for stimulus information: effects of amount of information

A concurrent-chain procedure was used to study pigeons' preferences as a function of amount of information. Pigeons chose between two terminal links. Both terminal links ended in food reinforcement with probability (p) and in blackout with probability (1–p). One terminal link (noninformative link) was signalled by a stimulus uncorrelated with either food or blackout. The other terminal link (informative link) was signalled by stimuli correlated with these outcomes. Amount of information conveyed by these stimuli was varied across conditions by changing the probability of reinforcement (p) and blackout (1–p). The pigeons strongly preferred the informative link, and preferences were greater at p values above 0.50 than for their complements. The pigeons engaged in different behaviors during the stimulus periods, suggesting that the value of informative stimuli may be in their function as discriminative stimuli for interim activities and terminal responses.     

Sub-Optimal Choice by Pigeons: Failure to Support The Allais Paradox

Pigeons show a preference for an alternative that provides them with discriminative stimuli (sometimes a stimulus that predicts reinforcement and at other times a stimulus that predicts the absence of reinforcement) over an alternative that provides them with nondiscriminative stimuli, even if the nondiscriminative stimulus alternative is associated with 2.5 times as much reinforcement (Stagner & Zentall, 2010). In Experiment 1 we found that the delay to reinforcement associated with the nondiscriminative stimuli could be reduced by almost one half before the pigeons were indifferent between the two alternatives. In Experiment 2 we tested the hypothesis that the preference for the discriminative stimulus alternative resulted from the fact that, like humans, the pigeons were attracted by the stimulus that consistently predicted reinforcement (the Allais paradox). When the probability of reinforcement associated with the discriminative stimulus that predicted reinforcement was reduced from 100% to 80% the pigeons still showed a strong preference for the discriminative stimulus alternative. Thus, under these conditions, the Allais paradox cannot account for the sub-optimal choice behavior shown by pigeons. Instead we propose that sub-optimal choice results from positive contrast between the low expectation of reinforcement associated with the discriminative stimulus alternative and the much higher obtained reinforcement when the stimulus associated with reinforcement appears. We propose that similar processes can account for sub-optimal gambling behavior by humans.     

Reinforcement magnitude effects in first- and second-order conditioning of directed action

Three experiments investigated the effects of reinforcement magnitude on conditioned key pecking in pigeons. Experiment 1, which included between-groups and within-subject designs, yielded significant effects of unconditioned stimulus (US) magnitude on the within-conditioned stimulus (CS) distribution of key pecks and on choice behavior, but no effect on the overall rate of key pecking. Experiment 2 employed a larger US-magnitude difference in a within-subject design. This manipulation resulted in differential rates of key pecking as well as a significant choice effect and differential within-CS key-peck distributions. A second-order conditioning procedure was used in Experiment 3, in which diffuse, visual stimuli (S1's) served as Pavlovian reinforcers for two key-light S2's. The S1 previously paired with a large US was more effective in conditioning second-order key-peck behavior to an S2 than was the S1 paired with a small US. The results of these experiments demonstrate that the associative effects of US magnitude can be expressed in the strength of CS-directed motor responding. The distinctive within-CS key-peck distributions in first-order conditioning suggests an interaction between CS- and US-directed responses.     

Brief presentations are sufficient for pigeons to discriminate arrays of same and different stimuli

Four pigeons first learned to discriminate 16-item arrays of same from different pictorial stimuli. They were then tested with reduced exposure to the pictorial arrays, brought about by changes in the stimulus viewing requirement under fixed-ratio (FR) and fixed-interval (FI) schedules. Increasing the FR requirement enhanced discriminative performance up to 10 pecks; increasing the FI requirement enhanced discriminative performance up to 5 s. Exposures to the stimulus arrays averaging only 2 s supported reliable discrimination. Pigeons thus discriminate same from different stimuli with considerable speed, suggesting that same-different discrimination behavior is of substantial adaptive significance.     

A diffusion model account of response time and accuracy in a brightness discrimination task: fitting real data and failing to fit fake but plausible data

A brightness discrimination experiment was performed to examine how subjects decide whether a patch of pixels is “bright” or “dark,” and stimulus duration, brightness, and speed versus accuracy instructions were manipulated. The diffusion model (Ratcliff, 1978) was fit to the data, and it accounted for all the dependent variables: mean correct and error response times, the shapes of response time distributions for correct and error responses, and accuracy values. Speed-accuracy manipulations affected only boundary separation (response criteria settings) in the model. Drift rate (the rate of accumulation of evidence) in the diffusion model, which represents stimulus quality, increased as a function of stimulus duration and stimulus brightness but asymptoted as stimulus duration increased from 100 to 150 msec. To address the argument that the diffusion model can fit any pattern of data, simulated patterns of plausible data are presented that the model cannot fit.