Sign and goal tracking during delay and trace autoshaping in pigeons

In two experiments, pigeons were exposed to an autoshaping procedure in which a keylight was followed by food under delay or trace conditions, while measures were taken of keypecking and time spent near the key. In Experiment 1, the birds in the trace group spent less time near the key than did the delay birds. Moreover, the trace birds exhibited a pattern of withdrawal from the key during the trial. In Experiment 2, visual observations of the birds’ location and latencies to eat both indicated that the trace birds’ withdrawal from the conditioned stimulus was accompanied by goal tracking. The difference in performance between the delay and trace conditions was taken as evidence that a trace stimulus may exert control over behavior as an occasion setter.     

Serial discrimination reversal learning in pigeons as a function of intertrial interval and delay of reinforcement

Pigeons learned a series of reversals of a simultaneous red-green visual discrimination. Delay of reinforcement (0 vs. 2 sec) and intertrial interval (ITI; 4 vs. 40 sec) were varied across blocks of reversals. Learning was faster with 0-sec than with 2-sec delays for both ITI values and faster with 4-sec ITIs than with 40-sec ITIs for both delays. Improvement in learning across successive reversals was evident throughout the experiment, furthermore, even after more than 120 reversals. The potent effects of small differences in reinforcement delay provide evidence for associative accounts and appear to be incompatible with accounts of choice that attempt to encompass the effects of temporal parameters in terms of animals’ timing of temporal intervals.     

Systematic errors in pigeons’ memory for event duration: Interaction between training and test delay

Pigeons trained to choose different stimuli following short- and long-duration signals make disproportionately more “short” choices (i.e., “choose-short errors”) following an increase in the retention interval and more “choose-long errors” following a decrease in this delay. The present experiment provided a systematic investigation of how these selective errors depend on the relationship between the training delay and the test delay. Pigeons were first trained with a 0-sec delay between the signal (2- or 8-sec food presentations) and the choice stimuli (red- and blue-lit keys). On subsequent test trials with 5- and 10-sec delays, choose-short errors predominated. Next, the birds were trained with a constant 10-sec delay and then tested with shorter or longer delays on some trials. The birds now responded accurately and without selective errors at the 10-sec training delay, but made choose-long errors at shorter delays and choose-short errors at longer delays. Finally, the birds were trained with a constant 20-sec delay and then tested with shorter and longer delays. Choose-long errors again appeared at shorter test delays, choose-short errors at longer test delays, and no differential errors at the 20-sec training delay. The selectivity of these errors generally increased with the absolute difference between the training and test delay. Theoretical implications of these results are discussed.     

Two-choice conditional discrimination performance of pigeons as a function of reward expectancy,prechoice delay,and domesticity

In a discrete-trial two-choice conditional discrimination task, pigeons which received food for a correct choice following the presentation of one cue and water for a correct choice following another cue performed better than pigeons which received food and water equally often in both cases when delays of several seconds intervened between the conditional cue and choice stimuli presentations. These results suggest that feedback properties of reinforcer-specific expectancies can be important in conditional discrimination learning in pigeons. An additional finding was that wild-caught pigeons regularly exhibited a higher percentage of correct choices than domestic subjects.     

Domestic pigeons (Columba livia) discriminate between photographs of male and female pigeons

We investigated whether pigeons are able to discriminate color photographs of male and female pigeons, using a categorical discrimination procedure. In Experiments 1 and 2B, 10 out of 14 pigeons learned the discrimination. Of these, 5 pigeons showed transfer to novel stimuli, demonstrating the categorical nature of the trained discrimination. Experiment 3 showed that the discriminative behavior was based primarily on the body, as opposed to the head and the neck region. In 1 out of 3 pigeons, the discriminative behavior was maintained by the black-and-white photographs. The results suggest that some pigeons have the ability to discriminate the sex of conspecifics without behavioral cues.     

Domestic pigeons (Columba livia) discriminate between photographs of individual pigeons

In two experiments, we examined the discrimination of photographs of individual pigeons by pigeons, using go/no-go discrimination procedures. In Experiments 1A and 1B, the pigeons were trained to discriminate 4 photographs of one pigeon from those of a number of pigeons. The subjects learned the discrimination, but their discriminative behavior did not transfer to new photographs taken from novel perspectives. When the pigeons were trained to discriminate between 20 photographs of five pigeons taken from four perspectives as the S+ and 20 photographs of five different pigeons as the S-, the subjects learned the discrimination, and this discriminative behavior partially transferred to new photographs taken from novel perspectives (Experiments 2A-2C). The results suggest that pigeons are able to discriminate among conspecific individuals, using stationary visual cues. This strengthens the assumption in evolutionary theory that animals can discriminate among individuals and encourages further investigation as to how this ability is used in various behaviors of animals.     

Choice and percentage reinforcement in pigeons

Pigeons responded on a two-key concurrent chains choice procedure with the same level of percentage reinforcement on each key. During the initial links, a choice response on either key occasionally produced a conditioned reinforcer—which on one key was associated with a 15-sec, and on the other key with a 30-sec, interreinforcement interval—or an extinction stimulus. In Part 1, the initial links were equal. With successive decreases in the probability of a reinforcer, choice shifted from preference for the 15-sec terminal link toward indifference. In Part 2, the initial links were unequal and were arranged so that the shorter initial link preceded the 30-sec terminal link. At a high probability of a reinforcer, the pigeons again preferred the 15-sec terminal link. However, at a low probability, the pigeons reversed and preferred the alternate key. It was concluded that the conditioned reinforcers tended to become functionally equivalent at a low probability of a reinforcer, despite the nominally different interreinforcement intervals, with the result that choice was then modulated by the relative size of the initial links. The data are inconsistent with the view that choice and the strength of conditioned reinforcers are isomorphic with the reduction in delay to reward correlated with terminal link stimuli.     

Form perception and attention in pigeons

This report selectively reviews the authors’ research on stimulus control by visual forms. Most studies employed visual search of computer-generated displays, and the main behavioral measure was search reaction time. Pigeons classify simple line forms much as do humans, and there was some evidence for feature extraction, though a search asymmetry probe failed to identify several putative features. Dimensional analysis revealed a new quantitative relation between similarity and the probability of detecting a target. It also identified candidates for integral and separable stimulus dimensions. Similarity and set-size variables influenced the extent to which attention was engaged. Further studies addressed the manner in which attention is focused, revealing relationships between priming and search images. In these cases, attention to a selected form is probably driven by a top-down assessment of predictability.     

Prospective and retrospective timing by pigeons

Pigeons discriminated between two pairs of durations: a short set (2.5 and 5 sec) and a long set (5 and 10 sec). The pairs were intermixed within sessions and identified by the colors on the signal and choice keys. Once the task was learned, the pigeons experienced the following three conditions seriatim: (1) The signal key was made ambiguous about the test change, but the choice keys were informative (retrospective); (2) the signal key identified the test range, but the choice keys did not (prospective); (3) probe trials were introduced in which the color of the center key signaled one test range, but the color of the choice keys signaled the other test range (inconsistent). Accuracy of choice decreased in the retrospective condition and, returned to baseline levels, was higher under the prospective condition than under the retrospective condition. In a final condition, referred to as conflict trials, the center-key color signified one test range and the choice-key colors the other range. The results from these conflict-inconsistent tests indicate that choice behavior was largely controlled by the signal-key color and not by the choice-key color. We relate these findings to different approaches to timing in animals.     

Transverse patterning in pigeons

Pigeons were trained to choose between colored lights (A, B, C, and D), first in a two-pair ambiguouscue problem (A+B?, B+C?), and then, with all colors nondifferentially reinforced, in a three-pair loop problem (A+B?, B+C?, C+A?) followed by a four-pair loop problem (A+B?, B+D?, D+C?, C+A?). Systematic efforts were made to simulate the data with a variety of models incorporating one or another of three conceptions of stimulus compounding prominent in the literature on compound conditioning. One conception is that the components of a compound stimulus are altered by interaction; the second is that they are not altered, but only supplemented with a new (compound-unique) component generated in the interaction; and the third is that the components entirely disappear in a configurational transformation. The ambiguous-cue data could be simulated accurately with each of the models, but the loop data with none of them. A convincing explanation of performance in loop problems remains to be found.     

Controlled processing in pigeons

This paper investigates whether rehearsal, or posttrial processing, of information about an event can be modulated by instructions in infrahuman organisms. Using pigeons, a procedure was developed for establishing a stimulus as a cue to disengage rehearsal, or posttrial processing, of a food reinforcer. Specifically, the stimulus instructed the animals to behave on a subsequent choice test as if food had not, in fact, been presented. Results are reported that suggest that this training was successful in establishing the stimulus as a cue to forget the occurrence of the food. These findings are interpreted as providing tentative support for the view that the cognitive repertoire of infrahuman organisms does include controlled processing strategies.     

Attempts to demonstrate magnetic discrimination by homing pigeons in flight

Eight homing pigeons, trained to fly between two elevated feeders within a flight tunnel, were tested for their ability to discriminate between two magnetic field stimuli and two acoustic stimuli, using a unitary discrete-trials procedure with successive presentation of stimuli. Magnetic stimuli consisted of the ambient magnetic field and a reduced magnetic field in which the vertical component of the field was reduced to 50% of its ambient value. Acoustic stimuli consisted of an ambient white noise and the white noise plus a tone. Stimuli were paired with food reward and either a time penalty (Experiment 1) or electric shock (Experiment 2). Although subjects could discriminate sounds with our procedures, none of the subjects demonstrated discrimination of magnetic fields. The failure of pigeons to discriminate magnetic stimuli is discussed as a consequence of either the failure to provide conditions sufficient for such discrimination or the absence of a magnetic sense in these animals.     

Children's Sensitivity to Lack of Understanding

Successful tutoring depends in part on child tutors’ ability to recognise and interpret accurately signals of misunderstanding by their tutees. Age- and gender-related differences were investigated in a study which exposed 80 children to a video-recorded episode involving a target child receiving ambiguous instructions in her attempts to move a model car along a designated route on a playmat roadway from one destination to another. The results showed that explicit, general and facial modes of displaying puzzlement by the target child were judged as equally powerful expressions of degree of puzzlement, but 8-10 year olds judged the target child as significantly more puzzled than did 7 year olds. Older children were also more likely to attribute the puzzlement of the target child to the ambiguous instructions than to her verbal or facial expression of puzzlement. Girls were generally more accurate than boys in judging facial expressions and less likely than boys to give wrong or alternatively ambiguous responses when given the opportunity to correct the video-recorded ambiguous instructions. The results throw some light on the developing sensitivities of boys and girls in recognising and attributing failures of understanding by other children.     

Categorical discrimination of objects and pictures by pigeons

With a three-choice instrumental discrimination procedure, pigeons were taught to distinguish small spherical objects from nonspherical objects. Spherical objects were defined as positive, nonspherical objects as negative. A device allowing an automatic presentation of the stimuli was employed. The subjects actually pecked the objects, and grain rewards were presented directly beside the correct objects. Acquisition was rapid, with the birds reaching a criterion of 80% correct choices within less than 150 trials. There was evidence that more than 200 objects were remembered individually over 3 months. Pigeons transferred the discrimination of spherical/nonspherical objects to novel objects. The criteria by which the birds judged the sphericity of objects seemed to be similar to those applied by humans. They could apply the categorization in a relational manner and generalize it to apply to photographs and drawings of objects. The categorization competence was retained for at least 3 months.     

Attempts to condition homing pigeons to magnetic cues in an outdoor flight cage

An attempt was made to train 9 homing pigeons to respond to the presence or absence of bar magnets by turning either left or right after flying the length of a 20-ft outdoor flight cage. During initial training, color cues were placed in front of feeding stations on the left and right sides of the cage. The color cues were paired with magnetic cues by attaching either bar magnets or brass bars to the backs of the birds. The color cues were then deleted, leaving only the magnetic cues. Each pigeon received about 300 trials of color training followed by about 200 trials of magnet testing. When only magnetic cues remained, none of the pigeons were able to choose the correct feeder at greater than chance levels of probability.     

Toddlers' Sensitivity to Standard Violations

Young children's emerging sensitivity to standard violations has been postulated, but not systematically examined, as an important aspect of early morality. In this study, we observed 100 26–41-month-old toddlers in contexts that involved standard violations. In one context, children were shown flawed and whole objects. In the other context, they were led to believe they had damaged the examiners' valued possessions ("mishaps"). When presented with the flawed and whole objects, toddlers expressed preference for the latter, but showed more interest in the former, thus indicating that the whole-flawed quality was salient. Verbal and nonverbal reactions reflecting sensitivity to the whole-flawed aspects were interrelated. Moreover, manifestations of sensitivity to flawed objects were associated with several behavioral and affective responses during the contrived mishaps (acceptance of responsibility, apologies, focus on reparations, and distress). Thus, sensitivity to standard violations in toddlerhood appeared to be a general phenomenon underlying different aspects of early morality.     

Dynamic object recognition in pigeons and humans

We investigated the role of dynamic information in human and pigeon object recognition. Both species were trained to discriminate between two objects that each had a characteristic motion, so that either cue could be used to perform the task successfully. The objects were either easy or difficult to decompose into parts. At test, the learned objects could appear in their learned motions, the reverse of the learned motions, or an entirely new motion, or a new object could appear in one of the learned motions. For humans, any change in the learned motion produced a decrement in performance for both the decomposable and the nondecomposable objects, but participants did not respond differentially to new objects that appeared in the learned motions. Pigeons showed the same pattern of responding as did humans for the decomposable objects, except that pigeons responded differentially to new objects in the learned motions. For the nondecomposable objects, pigeons used motion cues exclusively. We suggest that for some types of objects, dynamic information may be weighted differently by pigeons and humans.     

Contextual stimuli and memory retrieval in pigeons

Pigeons were given free-operant successive discrimination training in which, on alternate days, two different interdimensional problems were employed (color positive and line angle negative; a different color negative and a different line angle positive). Between days, these problems could be construed as intradimensional ones. For one group, training was conducted on each problem in the presence of the same ambient (contextual) stimuli, while for a second group each problem was trained in a different context. For a third group, these two contexts were randomly related to the problems. Postdiscrimination stimulus generalization gradients showed that peak shifts were obtained in both the same context and the random context groups, but no peak shifts were found for the group which learned each problem in a different context. Results were consistent with Spear’s (1973) treatment of animal memory which attributes retention test performance to the operation of a “context-elicited” retrieval process. An alternative uniprocess conditioning account of these and similar data was also discussed.     

Blocking of first- and second-order autoshaping in pigeons

In Experiment 1, the development of autoshaped pecking to a keylight signaling food was blocked if the keylight was presented only in conjunction with another stimulus already established as a signal for food, even though the blocking stimulus (either an overhead light or a train of clicks) never elicited pecking itself. In Experiment 2, pigeons came to peck a white keylight which signaled the presentation of a red keylight which had earlier been established as a first-order signal for food, but this second-order autoshaping was blocked if the white keylight was presented only in conjunction with the houselight or clicker which had previously signaled the presentation of the first-order stimulus. Second-order autoshaping was thus blocked in the same way as was first-order autoshaping.     

The role of test stimuli in matching to compound samples by pigeons

Two pigeons matched to sample in a three-key operant conditioning chamber. In Experiment I, two different kinds of samples were presented on the center key.Element samples were members of one of two sample sets — colors (a red or blue disk) or lines (a vertical or horizontal orientation of a set of white lines). These samples were followed by their respective sample sets on the side keys as comparison stimuli.Compound samples consisted of a set of lines superimposed on a colored disk. Following these samples, either sample set could appear as comparison stimuli. Matching to compound samples was less accurate than matching to element samples. One interpretation is that sharing of attention among elements of a compound sample weakened stimulus control by each element. A different interpretation is that an element sample controlled matching better because it was physically identical to a comparison stimulus whereas a compound sample was not. Experiments II–IV evaluated this “generalization decrement” alternative by testing element- vs. compound sample control with both element and compound comparison stimuli. Irrelevant elements were added to form compound comparison stimuli, some of which were physically identical to a preceding compound sample, but never identical to an element sample. In all experiments, the addition of irrelevant elements of comparison stimuli reduced sample control. However, the generalization decrement hypothesis failed to predict how differences in performance maintained by element and compound samples were affected by different tests of sample control. Matching accuracy appeared to be independently determined by the number of elements in a sample and whether irrelevant elements were present during tests of sample control.