Transfer of value from S+ to S- in simultaneous discriminations in humans

When animals learn a simultaneous discrimination, some of the value of the positive stimulus (S+) appears to transfer to the negative stimulus (S-). The present experiments demonstrate that such value transfer can also be found in humans. In Experiment 1 humans were trained on 2 simple simultaneous discriminations, the first between a highly positive stimulus, A (1,000 points); and a negative stimulus, B (0 points); and the second between a less positive stimulus, C (100 points); and a negative stimulus, D (0 points). On test trials, most participants preferred B over D. In Experiments 2 and 3 the value of the 2 original discriminations was equated in training (A[100]B[0] and C[100]D[0]). In Experiment 2 the values of the positive stimuli were then altered (A[1,000]C[0]); again, most participants preferred B over D. In Experiment 3, however, when the values of B and D were altered (B[1,000]D[0]), participants were indifferent to A and C. Thus, the mechanism that underlies value transfer in humans appears to be related to Pavlovian second-order conditioning. Similar mechanisms may be involved in assimilation processes in social contexts.     

Mediational use of internal representations of food and no-food events by pigeons

Two experiments were conducted with pigeons to determine whether internal representations of food and no-food events can act as mediators in the formation of new associations. Specifically we asked if the representation of an anticipated event can replace the event itself in an established conditional discrimination. In Phase 1 of both experiments pigeons were differentially autoshaped to peck hue stimuli, only one of which was followed by access to food. In Phase 2 they were trained on a symbolic 0-delay matching-to-sample (DMTS) task with food and no-food samples and line-orientation comparisons. In Phase 3 the birds were tested on a symbolic DMTS task in which the hue stimuli from Phase 1 were substituted for the Phase 2 food-event samples. For the Pos group, the hue followed by food in Phase 1 was substituted for the food sample and the hue associated with no-food was substituted for the no-food sample so that the resulting sample/comparison pairings were consistent with the food-event mediator. For the Neg group the pairings were reversed so that the sample/comparison pairings were inconsistent with the food-event mediators. In Experiment 1, when the no-food event was the absence of an event, acquisition of the transfer task was significantly more rapid in the Pos than in the Neg condition. In Experiment 2, when the no-food event was the presentation of an empty food hopper, the Pos group transferred at a significantly higher level than the Neg group. The two experiments provide evidence that in pigeons, representations involving event anticipations can be substituted for, and are thus similar to, the events themselves.     

Rats’ acquisition of the ephemeral reward task

The ephemeral reward task provides a subject with a choice between two alternatives A and B. If it chooses alternative A, reinforcement follows and the trial is over. If it chooses alternative B, reinforcement follows but the subject can also respond to alternative A which is followed by a second reinforcement. Thus, it would be optimal to choose alternative B. Surprisingly, Salwiczek et al. (PLoS One 7:e49068, 2012. doi: 10.1371/journal.pone.00490682012) reported that adult fish (cleaner wrasse) mastered this task within 100 trials, whereas monkeys and apes had great difficulty with it. The authors attributed the species differences to ecological differences in the species foraging experiences. However, Pepperberg and Hartsfield (J Comp Psychol 128:298–306, 2014) found that parrots too learned this task easily. We have found that with a similar task pigeons are not able to learn to choose optimally within 400 trials (Zentall et al. in J Comp Psychol 130:138–144, 2016). In Experiment 1 of the present study, we found that rats did not learn to choose optimally in 840 trials; however, in Experiment 2 we added a prior commitment to the initial choice by increasing delay to reinforcement for the choice response from a single lever press to the first lever press after 20 s (FI20 s). In a comparable amount of training to Experiment 1, the rats learned to choose optimally. Although the use of a prior commitment increases the delay to reinforcement, it appears to reduce impulsive responding which in turn leads to optimal choice.     

Imitation by animals: how do they do it?

Imitation is of psychological interest in part because it has cognitive implications for how organisms view the behavior of others, relative to their own behavior. It implies the ability to take the perspective of another. For this reason, researchers have tried to distinguish imitation from other kinds of social learning and influence. In the two-action procedure, one of two response topographies is demonstrated, and the correlation between the topography demonstrated and the topography later used by the observer is a measure of imitation. Both pigeons and Japanese quail show response matching, despite the fact that from their perspective, their own behavior appears quite different from that demonstrated. Although imitation has been demonstrated in birds and several species of primates, researchers are still not certain what mechanisms underlie this ability.     

Absolute pitch: frequency-range discriminations in pigeons (Columba livia): comparisons with zebra finches (Taeniopygia guttata) and humans (Homo sapiens)

Absolute pitch (AP) is the ability to classify individual pitches without an external referent. The authors compared results from pigeons (Columba livia, a nonsongbird species) with results (R. Weisman, M. Njegovan, C. Sturdy, L. Phillmore, J. Coyle, & D. Mewhort, 1998) from zebra finches (Taeniopygia guttata, a songbird species) and humans (Homo sapiens) in AP tests that required classification of contiguous tones into 3 or 8 frequency ranges on the basis of correlations between the tones in each frequency range and reward. Pigeons' 3-range discriminations were similar in accuracy to those of zebra finches and humans. In the more challenging 8-range task, pigeons, like zebra finches, discriminated shifts from reward to nonreward from range to range across all 8 ranges, whereas humans discriminated only the 1st and last ranges. Taken together with previous research, the present experiments suggest that birds may have more accurate AP than mammals.     

Repeated cocaine experience facilitates sucrose-reinforced operant responding in enriched and isolated rats

The purpose of the present experiment was to determine whether repeated cocaine exposure differentially affects sucrose-reinforced operant responding in rats raised in an enriched condition (EC) or an isolated condition (IC). Specifically, the performance of EC and IC rats pressing a lever for sucrose under a high fixed-ratio schedule (FR 30) prior to and after 10 days of exposure to cocaine (15 mg/kg, i.p.) or saline was compared. Regardless of rearing condition, rats repeatedly exposed to cocaine had shorter reacquisition latencies to complete a sucrose-reinforced FR 30 task than saline controls. The results suggest that cocaine exposure may have cross-sensitized both EC and IC rats to the reinforcing effects of sucrose or sucrose-associated cues, thus facilitating reacquisition of operant responding.     

Evidence for detection of one duration sample and default responding to other duration samples by pigeons may result from an artifact of retention-test ambiguity

S. C. Gaitan and J. T. Wixted (2000) proposed that when pigeons are trained on a conditional discrimination to associate 1 duration sample with 1 comparison and 2 other duration samples with a 2nd comparison, they detect only the single duration, and on trials involving either of the 2 other duration samples, they respond to the other comparison by default. In 2 experiments, the authors show instead that pigeons lend to treat the retention intervals (such as those used by Gaitan and Wixted) as intertrial intervals, and thus, they tend to treat all trials with a delay as 0-s sample trials. The authors tested this hypothesis by showing that divergent retention functions do not appear when the retention interval is discriminably different from the intertrial interval.     

Imitation and affordance learning by pigeons (Columba livia)

The bidirectional control procedure was used to determine whether pigeons (Columba livia) would imitate a demonstrator that pushed a sliding screen for food. One group of observers saw a trained demonstrator push a sliding screen door with its beak (imitation group), whereas 2 other groups watched the screen move independently (possibly learning how the environment works) with a conspecific either present (affordance learning with social facilitation) or absent (affordance learning alone). A 4th group could not see the screen being pushed (sound and odor control). Imitation was evidenced by the finding that pigeons that saw a demonstrator push the screen made a higher proportion of matching screen pushes than observers in 2 appropriate control conditions. Further, observers that watched a screen move without a demonstrator present made a significantly higher proportion of matching screen pushes than would be expected by chance. Thus, these pigeons were capable of affordance learning.     

Required pecking alters judgments of the passage of time by pigeons

There is evidence that how humans perceive time is affected by the activity in which they are engaged when they are judging time. In humans, typically, the more demanding the task, the faster time seems to pass. We asked whether a similar effect could be found in pigeons. Pigeons were trained to discriminate between a short-(2-sec) and a long-(10-sec) duration stimulus. Depending on the color of the stimulus (white or blue), the pigeons were required to peck (at least once per second or the trial was aborted) or to refrain from pecking (pecks aborted the trial). Once these tasks had been acquired to a high degree, probe trials involving white and blue stimuli were presented at durations between 2 and 10 sec. On trials in which the pigeons were required to peck, the point of subjective equality (i.e., the point at which pigeons are equally likely to choose the stimulus associated with long stimuli as the stimulus associated with short stimuli) was almost 1 sec longer than on trials in which the pigeons were required to refrain from pecking. In other words, on trials that required pecking, more time passed before the pigeons indicated that the probe duration was at the subjective midpoint between 2 and 10 sec than on trials that did not require pecking. This result suggests that like humans, the pigeons underestimated the passage of time when they were active or when attention to time-related cues had to be shared with attention to satisfying the response rate requirement.     

Timing in pigeons: effects of the similarity between intertrial interval and gap in a timing signal

Previous research suggests that when a fixed interval is interrupted (known as the gap procedure), pigeons tend to reset memory and start timing from 0 after the gap. However, because the ambient conditions of the gap typically have been the same as during the intertrial interval (ITI), ambiguity may have resulted. In the present experiment, the authors found that when ambient conditions during the gap were similar to the ITI, pigeons tended to reset memory, but when ambient conditions during the gap were different from the ITI, pigeons tended to stop timing, retain the duration of the stimulus in memory, and add to that time when the stimulus reappeared. Thus, when the gap was unambiguous, pigeons timed accurately.