Prospective timing in pigeons: Isolating temporal perception in the time-left procedure

In the time-left procedure, a task used to study prospective timing, animals choose between two stimuli that signal different delays to reinforcement. Trials begin with one stimulus signaling C seconds to reinforcement and, at different moments since its onset, another stimulus, signaling S seconds to reinforcement, with C > S, is introduced. Optimal performance consists in choosing the stimulus signaling the shorter time to reinforcement. Animals have been found to perform in this optimal way. However, this procedure is complex and variables other than time may be responsible for the results. In two experiments with pigeons we sought to improve the time-left procedure to better isolate the effect of time in the animals’ behavior. We attempted to control for two confounding variables, the asymmetry in the time markers from training to testing and the cost of switching between the two response alternatives. We conclude that in the time-left task pigeons seem indeed to regulate their behavior based on time because, with our improved procedure, they still chose the stimulus associated with the shorter time to food. However, our version of the procedure created new interpretative difficulties, strengthening the idea that the time-left procedure may be too complex to study timing.     

Matching-to-sample by pigeons: the dissociation of comparison choice frequency from the probability of reinforcement

It has been proposed that comparison choice in matching-to-sample should depend on two factors, the relative probability of reinforcement associated with each of the comparison stimuli and the conditional probability of each comparison stimulus being correct given presentation of one of the samples. DiGian and Zentall [DiGian, K.A., Zentall, T.R., 2007. Matching-to-sample in pigeons: in the absence of sample memory, sample frequency is a better predictor of comparison choice than the probability of reinforcement for comparison choice. Learn Behav. 35, 242-261] have shown that sample frequency together with the probability of choosing each of the comparison stimuli in training can influence comparison choice when delays are introduced, when the number of reinforcements associated with each of the comparison stimuli is equated. Furthermore, Zentall and Clement [Zentall, T.R., Clement, T.S., 2002. Memory mechanisms in pigeons: Evidence of base-rate neglect. J. Exp. Psych.: Anim. Behav. Proc. 28, 111-115] have found that sample frequency can affect comparison choice when delays are introduced independently of the number of choices of each of the comparison stimuli in training and the number of reinforcements associated with each of the comparison stimuli is equated. In the present experiment we found that the probability of choosing each of the comparison stimuli in training can affect comparison choice when delays are introduced, independently of sample frequency and when the number of reinforcements associated with each of the comparison stimuli is equated. Together, these experiments suggest that when the sample is not available, there is a partial dissociation between comparison choice and the probability of reinforcement associated with each of the comparison stimuli.     

A direct effect of competition on food choice by pigeons

Previous research on food choice of pigeons foraging alone and in competition showed an indirect response to the competitor, mediated by the resource depletion associated with the competitor. This experiment showed, in addition, that pigeons can adjust their food choice in direct response to the competitor itself. Pigeons foraged for large, preferred grains of maize and smaller, unpreferred grains of wheat presented in bowls covered with sawdust. In a within-subject design, pigeons were tested alone or in competition with another pigeon. In competition, a higher choice proportion of the wheat grains was observed on the first two choices out of 48 items, and this effect increased with time in the experiment. This result underscores the role of learning in group foraging behaviour. It also suggests a possible ecological implication: that individuals that learn faster may enjoy a competitive advantage in terms of reduced delay in responding to the presence of a conspecific.     

Testing meter, rhythm, and tempo discriminations in pigeons

Rhythmic grouping and discrimination is fundamental to music. When compared to the perception of pitch, rhythmic abilities in animals have received scant attention until recently. In this experiment, four pigeons were tested with three types of auditory rhythmic discriminations to investigate their processing of this aspect of sound and music. Two experiments examined a meter discrimination in which successively presented idiophonic sounds were repeated in meters of different lengths in a go/no-go discrimination task. With difficulty, the birds eventually learned to discriminate between 8/4 and 3/4 meters constructed from cymbal and tom drum sounds at 180 beats per minute. This discrimination subsequently transferred to faster tempos, but not to different drum sounds or their combination. Experiment 3 tested rhythmic and arrhythmic patterns of sounds. After 40 sessions of training, these same pigeons showed no discrimination. Experiment 4 tested repetitions of a piano sound at fast and slow tempos. This discrimination was readily learned and showed transfer to novel tempos. The pattern of results suggests that pigeons can time periodic auditory events, but their capacity to understand generalized rhythmic groupings appears limited.     

Transitions between cooperative and non-cooperative responding in the 'Pigeon's Dilemma'

Two pigeons played Iterated Prisoner's Dilemma (IPD) against a simulated opponent pre-programmed to play ‘Tit-For-Tat’ (TFT) and ‘Random’ (RND) strategies. Each pigeon received differential amounts of access to food following choices of either ‘cooperate’ or ‘defect’ on a trial. After 1000 trials against TFT and 500 trials against RND, results indicated that choice allocation was optimal when the birds played against RND but was sub-optimal when the birds played against TFT. In order to determine why the pigeons responded suboptimally against TFT, a trial-by-trial analysis of the data was conducted. The analysis revealed that once a pigeon had received the ‘Sucker's’ payoff (S), it was more likely to defect and receive the ‘Temptation’ payoff (T) than to cooperate and receive the ‘Reward’ (R) payoff. Local reinforcement contingencies appear to determine suboptimal responding against TFT in the iterated Pigeon's Dilemma.     

Scrounger numbers and the inhibition of social learning in pigeons

Social foraging can inhibit the learning and performance of food-finding behaviours. Confusion, overshadowing and frequency-dependent payoffs may all contribute to the inhibition, but standard experimental procedures make the separation of these effects difficult. In this study, we combine characteristics of cage and aviary experiments and present either a single naive pigeon or groups of three naive pigeons with a pre-trained producer opening an apparatus in an aviary. All naive birds scrounged on the 3456 openings they witnessed. In a post-test given in the absence of other birds, all single scroungers opened the apparatus, but only one of the group-scrounging pigeons did. Scrounger numbers appear to play an important role in the inhibition of food-finding behaviour, suggesting that confusion is a major component of learning in a social context.     

Attention to uninformative features expressed by pigeons in a duration matching-to-sample task

Pigeons were trained on a matching-to-sample task in which they had to respond to a different choice stimulus following the same durations (2 or 10 s) of two different signals. The duration signals consisted of a white light presented from the ceiling and a red light presented from the front wall. Subsequent test performance indicated that matching accuracy declined (1) when the set of choice stimuli following a duration signal differed from the set presented during training, and (2) when the color or location of the duration signal was changed from values used during training. These results are discussed in terms of attention to uninformative features of a visual stimulus.     

The matching law and effects of reinforcer rate and magnitude on choice in transition

Four pigeons responded in a concurrent-schedule procedure in which reinforcer rates and magnitudes changed unpredictably across sessions according to independent random series. Programmed relative reinforcement rates and magnitudes were always either 2:1 or 1:2. Pigeons' response allocation tended to stabilize within sessions and multiple regression analyses showed that it was determined by rates and magnitudes from the current session. Sensitivity coefficients were positive and statistically significant for current-session reinforcement and magnitude ratios. Although there were individual differences in sensitivity to rate and magnitude, their interaction was not significant across subjects. Rate and magnitude both controlled responding in single sessions and individual interreinforcer intervals. Analyses of responding within sessions showed that preference was more extreme when the richer rate and larger magnitude were associated with the same alternative than when they were associated with different alternatives. Overall, results support the concatenated generalized matching law's assumptions of additivity and independence as applied to choice in transition.     

Influence of the correlation modeling period on the prediction accuracy of infrared marker-based dynamic tumor tracking using a gimbaled X-ray head

PurposeTo assess the utility of 10 s and 20 s modeling periods, rather than the 40 s currently used, in the clinical construction of practical correlation models (CMs) in dynamic tumor tracking irradiation using the Vero4DRT.MethodsThe CMs with five independent parameters (CM parameters) were analyzed retrospectively for 10 consecutive lung cancer patients. CM remodeling was performed two or three times per treatment session. Three different CMs trained over modeling periods of 10, 20, and 40 s were built from a single, original CM log file. The predicted target positions were calculated from the CM parameters and the vertical displacement of infrared markers on the abdomen (P_IR) during the modeling. We assessed how the CM parameters obtained over modeling periods of T s (T = 10, 20, and 40 s) were robust to changes in respiratory patterns after several minutes. The mimic-predicted target positions after several minutes were computed based on the previous CM parameters and P_IR during the next modeling. The 95th percentiles of the differences between mimic-predicted and detected target positions over 40 s (E95_robust,T: T = 10, 20, and 40 s) were then calculated.ResultsStrong correlations greater than 0.92 were observed between the E95_robust,20 and E95_robust,40 values. Meanwhile, irregular respiratory patterns with inconsistent amplitudes of motion created differences between the E95_robust,10 and E95_robust,40 values of ≥10 mm.ConclusionsThe accuracies of CMs derived using 20 s were almost identical to those obtained over 40 s, and superior to those obtained over 10 s.     

Toward a framework for the evaluation of feature binding in pigeons

Pigeons were trained in a new procedure to test for visual binding errors between the dimensions of color and shape. In Experiment 1, pigeons learned to discriminate a target compound from 15 non-target compounds (constructed from four colors and shapes) by choosing one of two hoppers in a two-hopper choice task. The similarity of the target to non-target stimuli influenced choice responding. In Experiment 2, pigeons learned to detect a target compound when presented with a non-target compound within the same trial under conditions of simultaneity and sequentiality. Non-target trials were arranged to allow for the testing of binding errors (i.e., false identifications of the target on certain non-target trials). Transient evidence for binding errors in two of the birds occurred at the start of two-item training, but decreased with training. The experiments represent an important step toward developing a framework for the evaluation of visual feature binding in nonhumans.     

Reward magnitude and timing in pigeons

We investigated the interaction of motivation and timing by manipulating the expected reward magnitude during a peak procedure. Four pigeons were tested with three different reward magnitudes, operationalized as duration of food access. Each stimulus predicted a different reward magnitude on a 5 s fixed-interval schedule. Trials with different reward magnitudes were randomly intermingled in a session. Most pigeons responded less often and started responding later on peak trials when a smaller reward was expected, but showed no differences in response termination or peak times. Reward magnitude was independently corroborated through unreinforced choice trials, when pigeons chose between the three stimuli presented simultaneously. These results contribute to a growing body of evidence that the expected reward magnitude influences the decision to start anticipatory responding in tasks where the reward becomes available after a fixed interval, but does not alter peak times, nor the decision to stop responding on peak trials.     

Training delays reduce the choose-short effect with keylight, but not with food, duration samples in pigeons

Pigeons were trained to match 2- and 8-s food samples. The delay on training trials was either 0s (group 0sF), 5s (group 5sF), or varied between 2 and 8s (M=5s, group 5sV). Testing at a delay that exceeded the training delay by 15s in each group revealed a robust choose-short effect in each group. The same pigeons then reacquired a previously trained matching task involving 2- and 8-s keylight samples. Different comparison stimuli were used on food-sample and keylight-sample trials. The delay on training trials was the same on both food- and keylight-sample trials. Extended-delay testing revealed a robust choose-short effect in all three groups when the durations were conveyed by food presentations, but only group 0sF revealed a choose-short effect when the durations were conveyed by keylight presentations. Hence, training with a nonzero delay, whether fixed or variable, reduces the choose-short effect with keylight durations but not with food durations. It was concluded that at least some of the psychological processes mediating performance differ as a function of the event that conveys the duration.     

Spatial associative memory: a possible species difference in rats and pigeons

Previous research has shown that pigeons can remember which of four spatially distinct responses was last reinforced, for at least 72 h. The present study sought to replicate this finding using rats. Rats were tested in an operant chamber containing four spatially distinct levers. In each session one lever was randomly selected to provide reinforcement for 15 min. This reinforced period was preceded by a non-reinforced period that was 30 s long, on average. During the non-reinforced period the amount the rat pressed on the previously reinforced lever was compared to responding on the other three levers, and was taken as a measure of memory. Sessions were separated either by 17 min, 24 or 72 h. Unlike pigeons, rats responded at chance levels following each of these retention intervals. This finding adds to previous research suggesting differences in cognitive processes in rats and pigeons.     

Transitive inference in pigeons: measuring the associative values of Stimuli B and D

Several reinforcement-based models have been proposed to explain transitive-like behavior in nonverbal transitive inference tasks. These models assume that the initial training required for memorizing the premises produces an ordered series of associative values (A>B>C>D>E); these values can then be used to select the "transitively correct" stimulus in a novel pair (e.g., BD). Our study experimentally tested this assumption by using resistance-to-extinction and resistance-to-reinforcement techniques to obtain empirical measures of associative strength for Stimuli B and D. We first measured the associative strengths of these stimuli after completion of initial training with overlapping pairs of colored squares (A+B-, B+C-, C+D-, and D+E-) using resistance-to-extinction and resistance-to-reinforcement procedures. Next, we used massed presentations of Pair D+E- (termed bias reversal) that ought to increase the associative value of Stimulus D, and again measured the associative strengths of the stimuli. None of our experimental measures of associative strength correlated with pigeons' behavior in the BD test or with BD performance predicted by associative models either before or after bias reversal (Wynne, 1995; Siemann and Delius, 1998). These results question validity of reinforcement-based models for explaining animals' behavior in nonverbal TI tasks.     

Discounting the freedom to choose: implications for the paradox of choice

Organisms prefer to make their own choices. However, emerging research from behavioral decision making sciences has demonstrated that there are boundaries to the preference for choice. Specifically, many decision makers find an extensive array of choice options to be aversive, often leading to negative emotional states and poor behavioral outcomes. This study examined the degree to which human participants discounted hypothetical rewards that were (a) delayed, (b) probabilistic, and (c) chosen from a large array of options. The present results suggest that the "paradox of choice" effect may be explained within a discounting model for individual patterns of decision making.     

Reward context determines risky choice in pigeons and humans

Whereas humans are risk averse for monetary gains, other animals can be risk seeking for food rewards, especially when faced with variable delays or under significant deprivation. A key difference between these findings is that humans are often explicitly told about the risky options, whereas non-human animals must learn about them from their own experience. We tested pigeons (Columba livia) and humans in formally identical choice tasks where all outcomes were learned from experience. Both species were more risk seeking for larger rewards than for smaller ones. The data suggest that the largest and smallest rewards experienced are overweighted in risky choice. This observed bias towards extreme outcomes represents a key step towards a consilience of these two disparate literatures, identifying common features that drive risky choice across phyla.     

Consistency, transitivity and inter-relationships between measures of choice in environmental preference tests with chickens

Choice experiments are a widespread method of assessing the welfare requirements of domestic animals but prior predictions about what animals should choose to maximise their welfare are not possible. It is therefore important to analyse the data from sets of choice tests to establish whether intra-set and inter-set consistency in choice occurs. Strong inter-set consistency (transitivity) would provide support for the assumption that animals are maximising a complex utility (welfare) that may map onto their subjective state. We housed 56 hens Gallus gallus sequentially in three environments, experienced as three sets (A vs B; B vs C; A vs C), over a 40-week period. At the end of each set, each chicken made six choices between the items in that set, using T-maze testing procedures. The chickens showed significantly greater within-set consistency than expected by chance (p < 0.001 for all sets). Although different chickens exhibited different environmental preferences, we also found that a high within-set consistency was associated with faster decision-making (p < 0.001). When the three sets of choice trials for each hen were compared there was some evidence that the birds made more transitive choices (indicating consistent choices between sets) than expected by chance.     

Scaling relative incentive value: different adjustments to incentive downshift in pigeons and rats

Previous research suggests that pigeons and rats show differences in their behavioral adjustments in spaced-trial, incentive-downshift situations. Also, Papini and Pellegrini [Papini, M.R., Pellegrini, S., 2006. Scaling relative incentive value in consummatory behavior. Learn. Motiv. 37, 357-378] and Pellegrini and Papini [Pellegrini, S., Papini, M.R., 2007. Scaling relative incentive value in anticipatory behavior. Learn. Motiv. 38, 128-154] showed that changes in the rat's lever-pressing performance, runway running, and consumption of sucrose solutions after downshifts in incentive magnitude were a function of the ratio of postshift/preshift incentive magnitudes. Here, two experiments using a Pavlovian autoshaping procedure studied the adjustment of pigeons and rats to changes in incentive magnitude. In Experiment 1, pigeons received light-food pairings, whereas in Experiment 2, rats received lever-sucrose pairings. As a result, key-pecking and lever-pressing developed in each experiment, respectively. Preshift incentive magnitudes were downshifted so as to obtain postshift/preshift ratios of 0.125 and 0.25. Pigeons responded during the postshift phase according to the preshift incentive value and independently of the ratio value. However, rats showed ratio constancy, responding during the postshift in accordance with the postshift/preshift ratio, rather than with the absolute magnitudes of either the preshift or postshift incentives. These results support the comparative hypothesis that the mechanisms underlying ratio constancy during incentive downshifts are unique to mammals.     

Effects of thyrotropin-releasing hormone (TRH) and MK-771 on schedule-controlled behavior of squirrel monkeys, rabbits and pigeons

The effects of TRH (0.001-10.0 mg/kg) and a more potent TRH analog, MK-771 (0.001-5.6 mg/kg), were studied on comparable schedule-controlled performances of squirrel monkeys, rabbits and pigeons. Responding was maintained in the presence of different stimuli by a multiple fixed-ratio (FR), fixed-interval (FI) schedule of food presentation (monkeys and pigeons) or 0.25% saccharin solution (rabbits). Generally, TRH and MK-771 produced decreases in responding under both schedules and in all three species. TRH and MK-771 were roughly equipotent in the squirrel monkey, whereas in the pigeon and rabbit MK-771 was approximately 20 times more potent than TRH in decreasing responding to 50 percent of control levels. The duration of action of doses of TRH and MK-771 that reduced responding to 50 percent of control was approximately 3 hr in the squirrel monkey; recovery of performance occurred twice as fast under the FR schedules. With the pigeon, TRH effects that produced 50 percent decreases in responding lasted over 6 hours, whereas behaviorally comparable doses of MK-771 lasted about 4 hours. With few exceptions, TRH and MK-771 appear to produce similar effects of schedule-controlled behavioral performances of the squirrel monkey, rabbit and pigeon. Compared to the effects of other behaviorally-active substances under these procedures, TRH and MK-771 exert a distinctive array of effects.     

Effects of unpredictable changes in initial-link duration on choice and timing

Four pigeons responded in a concurrent-chains procedure in which terminal-link schedules were fixed-interval (FI) 10 s and FI 20 s. Across sessions, the location of the shorter terminal-link changed according to a pseudorandom binary sequence. Each session, the variable-interval initial-link schedule value was sampled from a uniform distribution that ranged from 0.01 to 30 s. On some terminal links, food was withheld to obtain measures of temporal control. Terminal-link delays determined choice (log initial-link response ratios) and timing (start and stop times on no-food trials) measures, which stabilized within the 1st half of each session. Preference for the shorter terminal-link delay was a monotonically decreasing function of initial-link duration. There was no evidence of control by initial-link durations from previous sessions.