Simultaneous discrimination reversal learning in pigeons and humans: anticipatory and perseverative errors

Pigeons were trained on a two-choice simultaneous discrimination (red vs. green) that reversed midway through each session. After considerable training, they consistently made both anticipatory errors prior to the reversal and perseverative errors after the reversal, suggesting that time (or number of trials) into the session served as a cue for reversal. In Experiment 2, to discourage the use of time as a cue, we varied the location of the reversal point within the session such that it occurred semirandomly after Trial 10, 25, 40, 55, or 70. Pigeons still tended both to anticipate and to perseverate. In Experiment 3, we required 20 pecks to a stimulus on each trial to facilitate memory for the preceding response and sensitivity to local reinforcement contingencies, but the results were similar to those of Experiment 2. We then tested humans on a similar task with a constant (Experiment 4) or variable (Experiment 5) reversal location. When the reversal occurred consistently at the midpoint of the session, humans, like pigeons, showed a tendency to anticipate the reversal; however, they did not show perseverative errors. When the reversal location varied between sessions, unlike pigeons, humans adopted a win–stay/lose–shift strategy, making only a single error on the first trial of the reversal.     

Influence of intertrial interval duration on the intertrial agreement effect in delayed matching-to-sample with pigeons

Accuracy on even-numbered trials was assessed as a function of (1) the relation between the sample on the immediately preceding trial and that on the current trial and (2) the length of the intertrial interval (ITI) that intervened between odd- and even-numbered trials. A relatively long interval intervened between pairs of trials in the clustered-dyads procedure, whereas this interval was equal to the ITI in the massed-trials procedure. Both procedures revealed an intertrial agreement effect in that accuracy was higher when the sample on the immediately preceding trial was identical rather than opposite. A decrease in the magnitude of this effect at longer ITIs was apparent only in the clustered-dyads procedure. The insensitivity of the intertrial agreement effect to variations in ITI in the massed-trials procedure may reflect floor effects and the carryover of memory from multiple prior trials that mask the true magnitude of the intertrial agreement effect at short ITIs.     

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.     

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...     

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.     

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.     

Pretraining and discrimination reversal learning by rhesus monkeys

Groups of five to seven macaques were trained on repeated reversals of a visual (or spatial) discrimination habit after no pretraining, extended discrimination training, or repeated reversal training on spatial (or visual) cues. Neither sort of pretraining had a significant effect on reversal learning on the second cue. These results indicate that monkeys’ capacity to develop generalized “win-stay, lose-shift” hypotheses may have been exaggerated in previous experiments.     

The effects of intertrial and feature-target intervals on operant serial feature-positive discrimination learning

The effects of intertrial interval (ITI) and feature-target interval (FTI) on the nature of learning in discrete-trial operant serial feature-positive (feature → target+ / target?) discrimination training were examined in two experiments with rats. Discrimination performance was acquired more rapidly with longer ITIs and shorter FTIs. In contrast, transfer to a separately trained target was greater with shorter ITIs regardless of FTI. Persistence of discrimination performance after feature extinction was greater with longer ITIs. Only the last of these performance measures showed evidence for invariance with constant ITI/FTI ratios. The results are discussed in the context of theories of occasion setting.     

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.     

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.     

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.     

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.     

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.