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.     

The nature of discrimination learning in pigeons

The results from five experiments are considered in relation to two of Spence's (1937, 1938) proposals concerning discrimination learning. In Experiments 1 and 2, we investigated whether his ideas about the interaction between excitatory and inhibitory generalization gradients can be used to understand how animals solve a complex patterning discrimination. The results supported a development of his proposals as put forward by Pearce (1994), provided a modification was made to Pearce's rulefor determining the shape ofthe generalization gradient. In Experiments 3, 4, and 5, we examined whether animals would pay more attention to stimuli that are relevant, rather than irrelevant, to the solution of a discrimination. The results supported this proposal for stimuli comprising visual patterns, but not for those comprising plain colors. The results also indicated that change of attention was a consequence of preliminary receptor-exposure acts, as envisaged by Spence, and not of more central changes in attention.     

Midsession reversals with pigeons: visual versus spatial discriminations and the intertrial interval

Discrimination reversal learning has been used as a measure of species flexibility in dealing with changes in reinforcement contingency. In the simultaneous-discrimination, midsession-reversal task, one stimulus (S1) is correct for the first half of the session, and the other stimulus (S2) is correct for the second half. After training, pigeons show a curious pattern of choices: They begin to respond to S2 well before the reversal point (i.e., they make anticipatory errors), and they continue to respond to S1 well after the reversal (i.e., they make perseverative errors). That is, pigeons appear to be using the passage of time or the number of trials into the session as a cue to reverse, and are less sensitive to the feedback at the point of reversal. To determine whether the nature of the discrimination or a failure of memory for the stimulus chosen on the preceding trial contributed to the pigeons’ less-than-optimal performance, we manipulated the nature of the discrimination (spatial or visual) and the duration of the intertrial interval (5.0 or 1.5 s), in order to determine the conditions under which pigeons would show efficient reversal learning. The major finding was that only when the discrimination was spatial and the intertrial interval was short did the pigeons perform optimally.     

Conditioned inhibition in feature negative discrimination learning with pigeons

Discrimination performance was investigated with pigeons using feature negative (FN) discrimination procedures which differed in the temporal arrangement of the stimuli on S? trials. In both procedures, a single common element was presented on reinforced (S+) trials. In thesimultaneous FN procedure, a distinguishing element was presented simultaneously with the common element of S? trials. In thesequential FN procedure, the distinguishing element preceded onset of the common element on S? trials. In two experiments, the sequential FN procedure yielded better discrimination performance. In Experiment 1, a summation test designed to separate learning and performance variables indicated that sequential FN subjects had learned the negative relationship between the distinguishing element and reinforcement while simultaneous FN subjects had not. In Experiment 2, summation and acquisition tests indicated that the distinguishing element developed inhibitory properties in the sequential FN procedure but not in the simultaneous FN procedure.     

Response sequence learning as a function of primary versus conditioned reinforcement

Two groups of pigeons were required to generate a fixed sequence of responses on three keys, for example, middle-left-right. One group received a small food reward (S^Food) following each correct response except the terminal one, which was followed by a large food reward. The second group received conditioned reinforcement from an overhead light (S^Light) for each correct response, with the terminal correct response followed by both S^Light and the large food reward. We manipulated length of sequence (3 or 7 responses) and duration of required interresponse interval (IRI; 1 to 9 sec). S^Light contingencies generated more accurate performances than did S^Food when sequence length was 3 responses but not when it was 7 responses. IRI duration influenced accuracy under the S^Light contingencies but not under S^Food. These results show that conditioned reinforcers sometimes generate more accurate sequence learning than do primary reinforcers, and that schedule contigencies influence which type of feedback will optimize performance. The results parallel those from the matching-to-sample and conditional discrimination literature.     

The role of intertrial interval in the learning of two simple avoidance tasks

Learning & Behavior - Rats were trained to avoid shock in either a jump-up or a one-way running situation with intertrial intervals of 20 min to 3 h for different groups. The rats with the...     

Latent discrimination learning under a regular schedule of partial reinforcement

In this investigation, which employed rats in a runway, discriminative responding consisted of faster running on the reinforced than on the nonreinforced trials of either the 4NR or R4N schedule, both schedules containing fixed, repeated sequences of nonreinforced and reinforced trials. Under the 4NR schedule, four nonreinforced trials preceded a reinforced trial each day, and under the R4N schedule, a reinforced trial was followed by four nonreinforced trials each day. The major finding obtained was that under the 4NR schedule, discriminative responding was improved very substantially by a shift to extinction. Rats maintained on the 4NR schedule did not show improved discriminative responding, nor did discriminative responding improve in extinction following training under either the R4N schedule or a schedule of consistent reinforcement. Latent discrimination learning was defined as discriminative responding which fails to reflect adequately the amount of discrimination learning accomplished. The present findings demonstrate latent discrimination learning for regular schedules of partial reinforcement, something already demonstrated for brightness differential conditioning and possibly DRL schedules, as well.     

Asymmetry in the discrimination of quantity by rats: The role of the intertrial interval

In three experiments, rats were trained to discriminate between 20 and five (Exps. 1 and 2), or between 40 and five (Exp. 3), black squares. The squares were randomly distributed in the center of a white background and displayed on a computer screen. For one group, the patterns containing the higher quantity of squares signaled the delivery of sucrose (+), whilst patterns with the lower quantity of squares did not (–). For the second group, sucrose was signaled by the lower, but not by the higher, quantity of squares. In Experiment 1, the intertrial interval (ITI) was a white screen, and the 20+/5– discrimination was acquired more readily than the 5+/20– discrimination. For Experiment 2, the ITI was made up of 80 black squares on a white background. In this instance, the 5+/20– discrimination was acquired more successfully than the 20+/5– discrimination. In Experiment 3, two groups were trained with a 40+/5– discrimination, and two with a 5+/40– discrimination. For one group from each of these pairs, the training trials were separated by a white ITI, and the 40+/5– discrimination was acquired more readily than the 5+/40– discrimination. For the remaining two groups, the training trials were not separated by an ITI, and the two groups acquired the task at approximately the same rate. The results indicate that the cues present during the ITI play a role in the asymmetrical acquisition of magnitude discriminations based on quantity.     

Two independent effects of variation in intertrial interval upon leverpress avoidance learning by rats

Variation in the intertrial interval (ITI) preceding a given trial is shown to have an independent and opposite effect upon leverpress avoidance performance to that caused by variation in ITI after a trial. This finding accounts for the opposite effect of overall ITI upon leverpress avoidance to its effect upon one-way avoidance without recourse to an associative explanation. The implications of this finding for recent discussions of response constraints upon avoidance learning is discussed.     

Enhancement of pigeons’ conditional discrimination performance by expectancies of reinforcement and nonreinforcement

Prior work has shown that when the separate correct responses of a conditional discrimination are followed by different reinforcing outcomes, performance is enhanced relative to that obtained under the conventional, single-reinforcer procedure. Four experiments with pigeons yielded the analogous finding when the different outcomes were reinforcement and explicit nonreinforcement. Controls indicated that the results could not be attributed to the effects of intermittent reinforcement, to possible differences in cue duration, or to a variety of potential sources of conditioned reinforcement. An interpretation in terms of expectancy learning is proposed.     

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.     

Effect of age on discrimination learning,reversal learning,and cognitive bias in family dogs

Several studies on age-related cognitive decline in dogs involve laboratory dogs and prolonged training. We developed two spatial tasks that required a single 1-h session. We tested 107 medium-large sized dogs: “young” (N=41, aged 2.5–6.5 years) and “old” (N=66, aged 8–14.5 years). Our results indicated that, in a discrimination learning task and in a reversal learning task, young dogs learned significantly faster than the old dogs, indicating that these two tasks could successfully be used to investigate differences in spatial learning between young and old dogs. We also provide two novel findings. First, in the reversal learning, the dogs trained based on the location of stimuli learned faster than the dogs trained based on stimulus characteristics. Most old dogs did not learn the task within our cut-off of 50 trials. Training based on an object’s location is therefore more appropriate for reversal learning tasks. Second, the contrast between the response to the positive and negative stimuli was narrower in old dogs, compared to young dogs, during the reversal learning task, as well as the cognitive bias test. This measure favors comparability between tasks and between studies. Following the cognitive bias test, we could not find any indication of differences in the positive and negative expectations between young and old dogs. Taken together, these findings do not support the hypothesis that old dogs have more negative expectations than young dogs and the use of the cognitive bias test in older dogs requires further investigation.     

Reinstatement of postresponse stimuli prior to reward in delayed-reward discrimination learning by pigeons

Delayed-reward learning in pigeons was examined using a simultaneous red-green visual discrimination task in which the conditions during the delay interval were varied between groups. The nondifferential group received training in which the stimulus present during the 1-min delay was the same following a peck on the correct and incorrect colors. The other three groups received 1-min delay training in which different stimuli occurred in the delay interval following correct and incorrect choices. The differential group received continuous, differential stimuli during the delay. The reinstatement group received the differential stimuli in the 10 sec immediately following the choice and during the last 10 sec of the delay. The reversedcue group was treated in the same way, except that the 10-sec delay stimulus immediately following an incorrect response was also presented for 10 sec prior to reward on correct choices, and the stimulus following a correct response also occurred 10 sec before nonreward on incorrect choices. Nondifferential birds failed to learn the discrimination, while differential and reinstatement birds learned it readily. The reversed-cue birds learned to choose the incorrect stimulus. Differential and reinstatement birds showed no decrement in performance when the delay was increased to 2 min. These findings suggest that similarity of prereward and postresponse delay stimuli controls choice responding in long-delay learning, a finding compatible with both memorial and conditioned reinforcement interpretations.     

Effects of intertrial reward and/or nonreward placements during a 20-second intertrial interval on single-alternation training in rats

Seventy male hooded rats received single-alternation runway training in which goalbox placements were interpolated during the 20-sec intertrial interval. Placements provided alternating reward/ nonreward, random reward/nonreward, continuous reward, or continuous nonreward. Relative to nonplaced controls, alternation performance was reliably facilitated only by intertrial alternation placements which re-presented the goal event of each immediately preceding instrumental trial. All other intertrial procedures reliably impaired alternation performance. Degree of impairment was graded from least to most as follows: intertrial alternation placements with the goal event opposite to that of each immediately preceding instrumental trial, intertrial placements with continuous non-reward, intertrial placements with continuous reward, and intertrial placements with random reward/nonreward.     

Expectancies as mediators in the differential-reward conditional discrimination performance of pigeons

In a series of within-subject experiments employing a two-choice delayed conditional discrimination task, pigeons chose correctly more often when kind of correct choice and kind of reinforcer were perfectly correlated than when uncorrelated. Correct choice behavior fell to chance levels when the correlation was reversed or when it was removed by using only one kind of reinforcer. Implications for mediation theories are discussed, with the conclusion being that, although the possibility that instrumental mediators are present in this situation cannot be dismissed, the overall pattern of results indicates that classical mediators are of principal importance in this type of task.     

Conditioning of the nictitating membrane response of the rabbit (Oryctolagus cuniculus) as a function of length and degree of variation of intertrial interval

The study involved three experiments. The first, a parametric investigation of nictitating membrane conditioning with eight constant intertrial intervals (ITIs) between 5 and 120 sec, orthogonal to interstimulus intervals (ISIs) of 250 and 750 msec plus three temporal conditioning control groups, revealed that performance improved rapidly with increasing ITI but stabilized at relatively low ITI values. At 750-msec ISI, a decrement in performance was found at 60-sec ITI. Experiment II, using constant ITIs of 45–75 sec in 5-sec steps, at 750-msec ISI confirmed the trend toward a performance decrement around 60 sec, although the trend was weak and highly variable. Experiment III evaluated the differences in performance between constant and variable ITI, using three ITI values and three conditions of variation at each value. Findings were discussed in terms of differences in conditioning resulting from both length and degree of variation of ITI and some subtle effects which may emerge only when constant ITIs are used.     

Effects of preexposure and retention interval placement on latent inhibition and perceptual learning in a choice-maze discrimination task

In two experiments, we examined how preexposure to discriminative stimuli and introduction of a 21-day retention interval affected the latent inhibition (LI) and perceptual learning (PL) of rats in a choice-maze discrimination task. Experimental groups were preexposed to three wall patterns, one in each of three arms of a maze. Control groups were preexposed only to white arms. PL groups were trained to discriminate A versus B, and LI groups, to discriminate A or B versus C. The A and B patterns shared many elements not shared with the C pattern. In Experiment 1, both at the end of training and after the subsequent retention interval, the PL groups performed better than controls, whereas the LI groups performed worse. In Experiment 2, inserting the 21-day retention interval between preexposure and discrimination training disrupted final measures of LI but not PL performance. Implications for current concepts of PL and LI are discussed.     

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.     

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.