Thomas Zentall | University of Kentucky (original) (raw)

Papers by Thomas Zentall

Psychological Science, 1996

Providing evidence for imitative learning in animals has been made difficult by the need to contr... more Providing evidence for imitative learning in animals has been made difficult by the need to control for a number of possible nonimitation accounts (e.g., mere presence of another animal, attention drawn to a location, attention drawn to an object being manipulated) that often have not been recognized in previous research In the present experiment we used a version of the two-action method in which a treadle could be operated by a pigeon in one of two distinctive ways with its beak by pecking or with its foot by stepping What is unique in this experiment is not only the distinct response topographies, but also that both responses have the same effect on the environment (depression of the treadle followed by food reward) When pigeons that had observed one of the two response topographies were given access to the treadle, a significant correspondence was found between the topography of the observers responses and that of their respective demonstrators' responses

The Quarterly journal of experimental psychology. B, Comparative and physiological psychology, 1998

In a simple simultaneous discrimination involving a positive stimulus (S+) and a negative stimulu... more In a simple simultaneous discrimination involving a positive stimulus (S+) and a negative stimulus (S-), it has been hypothesized that positive value can transfer from the S+ to the S- (thus increasing the relative value of the S-) and also that negative value can transfer from the S- to the S+ (thus diminishing the relative value of the S+; Fersen, Wynne, Delius, & Staddon, 1991). Evidence for positive value transfer has been reported in pigeons (e.g. Zentall & Sherburne, 1994). The purpose of the present experiments was to determine, in a simultaneous discrimination, whether the S- diminishes the value of the S+ or the S- is contrasted with the S+ (thus enhancing the value of the S+). In two experiments, we found evidence for contrast, rather than value transfer, attributable to simultaneous discrimination training. Thus, not only does the S+ appear to enhance the value of the S-, but the S- appears to enhance rather than reduce the value of the S+.

Learning and Motivation, 1993

Journal of Experimental Psychology: Animal Behavior Processes, 1994

Behavioural Processes, 1998

Psychonomic Bulletin & Review, 2005

Serial pattern learning describes behavior in which a subject anticipates not only the time and e... more Serial pattern learning describes behavior in which a subject anticipates not only the time and effort needed for the next reinforcer but also the pattern of time and effort to reinforcers after the first. Chandel et al. (2021) found that pigeons left a progressive schedule (in which each reinforcer was successively harder to obtain) earlier than would have been optimal. They argued that the pigeons anticipated the harder to obtain reinforcers beyond the next one. In the present experiments, pigeons were trained on a progressive schedule for which each reinforcer was successively easier to obtain but the initial choice was between a fixed ratio schedule (FR23) for which a reinforcer was easier to obtain than the first reinforcer on the improving progressive schedule (32 pecks). Delayed discounting suggests that the pigeons would prefer the FR23 because more immediate reinforcers should be preferred, whereas serial pattern learning suggests that the progressive schedule might be pref...

Psychological Science, 1997

Zentall Sutton and Sherburne (1996) reported that pigeons observing a conspecific demonstrator ei... more Zentall Sutton and Sherburne (1996) reported that pigeons observing a conspecific demonstrator either step on or peck at a treadle to obtain food subsequently showed a significant tendency to manipulate the treadle as had their demonstrator Zentall et al suggested this finding showed observer pigeons had learned by imitation to peck at or step on the treadle However, the same result might have been obtained if pigeons had learned to step on the treadle by trial and error, and pigeons exposed to a treadle-pecking demonstrator had come to peck at the treadle as a result of nonimitative social-learning processes such as local enhancement or contagion Here we report the results for two control groups showing that pigeons do not learn to step on or peck at a treadle for food reward unless they observe a relevant demonstrator These results considerably strengthen the original conclusion Future research using the two action method to demonstrate imitative learning should include similar co...

Journal of Experimental Psychology: Animal Behavior Processes, 2005

(2005) proposed a hypothesis of timing in rats to account for the results of experiments that hav... more (2005) proposed a hypothesis of timing in rats to account for the results of experiments that have used the peak procedure with gaps. According to this hypothesis, the introduction of a gap causes the animal's memory for the pregap interval to passively decay (subjectively shorten) in direct proportion to the duration and salience of the gap. Thus, animals should pause with short, nonsalient gaps but should reset their clock with longer, salient gaps. The present authors suggest that the ambiguity of the gap (i.e., the similarity between the gap and the intertrial interval in both appearance and relative duration) causes the animal to actively reset the clock and prevents adequate assessments of the fate of timed intervals prior to the gap. Furthermore, when the intertrial interval is discriminable from the gap, the evidence suggests that timed intervals prior to the gap are not lost but are retained in memory.

Journal of Comparative Psychology, 2012

In delayed matching to sample, once acquired, pigeons presumably choose comparisons according to ... more In delayed matching to sample, once acquired, pigeons presumably choose comparisons according to their memory for (the strength of) the sample. When memory for the sample is sufficiently weak, comparison choice should depend on the history of reinforcement associated with each of the comparison stimuli. In the present research, pigeons acquired two matching tasks in which Sample S1 was associated with one comparison from each task, C1 and C3, whereas Sample S2 was associated with Comparison C2, and Sample S3 was associated with Comparison C4. As the retention interval increased, the pigeons showed a bias to choose the comparison (C1 or C3) associated with the more frequently occurring sample (S1). Thus, pigeons were sensitive also to the (irrelevant) likelihood that each of the samples was presented. The results suggest that pigeons may allow their reference memory for the overall sample frequency to influence comparison choice, independent of the comparison stimuli present.

Quarterly Journal of Experimental Psychology, 2011

Humans were trained on a temporal discrimination to make one response when the stimulus duration ... more Humans were trained on a temporal discrimination to make one response when the stimulus duration was short (2 s) and a different response when the stimulus duration was long (8 s). They were then tested with stimulus durations in between to determine the bisection point. In Experiment 1, we examined the effect of a secondary cognitive task (counting backwards by threes) on the bisection point when participants were trained without a cognitive load and were tested with a cognitive load or the reverse (relative to appropriate controls). When the cognitive load increased from training, the psychophysical function plotting long responses against the increase in stimulus duration shifted to the right (as if the internal clock slowed down), and when the cognitive load decreased from training the psychophysical function shifted to the left (as if the internal clock speeded up). In Experiment 2, when the secondary task consisted of exerting continuous force on a transducer (a physically eff...

Psychonomic Bulletin & Review, 2012

This study investigated whether initial selfcontrol exertion by dogs would affect behavioral appr... more This study investigated whether initial selfcontrol exertion by dogs would affect behavioral approach toward an aggressive threat. Dogs were initially required to exert self-control (sit still for 10 min) or not (caged for 10 min) before they were walked into a room in which a barking, growling dog was caged. Subject dogs spent 4 min in this room but were free to choose where in the room they spent their time. Approaching the unfamiliar conspecific was the predisposed response, but it was also the riskier choice (Lindsay, 2005). We found that following the exertion of self-control (in comparison with the control condition), dogs spent greater time in proximity to the aggressor. This pattern of behavior suggests that initial self-control exertion results in riskier and more impulsive decision making by dogs. Keywords Self-regulation. Dogs. Decision making. Risk taking. Impulsivity The potential for danger is ubiquitous. To avoid danger, people often exert self-control over their behavior (Baumeister, 1998; Baumeister, Heatherton & Tice, 1994). When people fail to exert self-control and behave more impulsively, they may unintentionally put themselves in harm's way (Freeman & Muraven, 2010). Pedestrians jaywalk across busy streets, children stick objects into electrical outlets, and teenagers join dangerous gangs. The failure to exert self-control and avoid these dangerous activities is likely affected by many individual variables (e.g., demographics, personality). However, a common mechanism that may be responsible for human and nonhuman self-control vigor may also play a role (Miller, Pattison, DeWall, Rayburn-Reeves & Zentall, 2010). The present research tested this hypothesis by examining whether dogs approach dangerous situations when their ability to exert self-control is compromised. Research with human and nonhuman animals suggests that self-control relies on a limited resource (Baumeister & Heatherton, 2004; Miller et al., 2010). Exerting self-control depletes this resource, and once depleted, subsequent efforts to control behavior become impaired. For example, when humans control their impulse to eat fresh cookies (in comparison to when they inhibit eating radishes), they then persist for a shorter time on an unsolvable puzzle task (Baumeister, Bratslavsky, Muraven & Tice, 1998). Dogs behave similarly. When dogs control their physical movement (in comparison with when self-control is not needed because they are physically constrained by a cage), they persist for a shorter duration on a subsequent unsolvable puzzle task (Miller et al., 2010). Extensive research with humans suggests that this phenomenon is domain general, suggesting that tasks that require selfcontrol negatively affect performance on a wide variety of subsequent tasks (for a review, see Baumeister, Schmeichel & Vohs, 2007). Decision making, for example, is negatively affected by initial self-control exertion. Depleted subjects, as compared with their nondepleted counterparts, take more risks and gamble more (Bruyneel, DeWitte, Franses & Dekimpe,

Psychonomic Bulletin & Review, 2014

When humans are asked to judge the value of a set of objects of excellent quality, they often giv... more When humans are asked to judge the value of a set of objects of excellent quality, they often give this set higher value than those same objects with the addition of some of lesser quality. This is an example of the affect heuristic, often referred to as the less-is-more effect. Monkeys and dogs, too, have shown this suboptimal effect. But in the present experiments, normally hungry pigeons chose optimally: a preferred food plus a less-preferred food over a more-preferred food alone. In Experiment 2, however, pigeons on a less-restricted diet showed the suboptimal less-is-more effect. Choice on control trials indicated that the effect did not result from the novelty of two food items versus one. The effect in the lessfood-restricted pigeons appears to result from the devaluation of the combination of the food items by the presence of the less-preferred food item. The reversal of the effect under greater food restriction may occur because, as motivation increases, the value of the less-preferred food increases faster than the value of the more-preferred food, thus decreasing the difference in value between the two foods.

Proceedings of the National Academy of Sciences, 2014

Significance Although scientists have identified surprising cognitive flexibility in animals and ... more Significance Although scientists have identified surprising cognitive flexibility in animals and potentially unique features of human psychology, we know less about the selective forces that favor cognitive evolution, or the proximate biological mechanisms underlying this process. We tested 36 species in two problem-solving tasks measuring self-control and evaluated the leading hypotheses regarding how and why cognition evolves. Across species, differences in absolute (not relative) brain volume best predicted performance on these tasks. Within primates, dietary breadth also predicted cognitive performance, whereas social group size did not. These results suggest that increases in absolute brain size provided the biological foundation for evolutionary increases in self-control, and implicate species differences in feeding ecology as a potential selective pressure favoring these skills.

Learning & Behavior, 2012

Consistent with human gambling behavior but contrary to optimal foraging theory, pigeons show a s... more Consistent with human gambling behavior but contrary to optimal foraging theory, pigeons show a strong preference for an alternative with low probability and high payoff (a gambling-like alternative) over an alternative with a greater net payoff (Zentall & Stagner, Proceedings of the Royal Society B, 278, 1203-1208, 2011). In the present research, we asked whether humans would show suboptimal choice on a task involving choices with probabilities similar to those for pigeons. In Experiment 1, when we selected participants on the basis of their self-reported gambling activities, we found a significantly greater choice of the alternative involving low probability and high payoff (gambling-like alternative) than for a group that reported an absence of gambling activity. In Experiment 2, we found that when the inhibiting abilities of typical humans were impaired by a self-regulatory depletion manipulation, they were more likely to choose the gambling-like alternative. Taken together, the results suggest that this task is suitable for the comparative study of suboptimal decision-making behavior and the mechanisms that underlie it.

Animal Learning & Behavior, 1999

L’Année psychologique, 2009

Distribution électronique Cairn.info pour NecPlus. Distribution électronique Cairn.info pour NecP... more Distribution électronique Cairn.info pour NecPlus. Distribution électronique Cairn.info pour NecPlus. La reproduction ou représentation de cet article, notamment par photocopie, n'est autorisée que dans les limites des conditions générales d'utilisation du site ou, le cas échéant, des conditions générales de la licence souscrite par votre établissement. Toute autre reproduction ou représentation, en tout ou partie, sous quelque forme et de quelque manière que ce soit, est interdite sauf accord préalable et écrit de l'éditeur, en dehors des cas prévus par la législation en vigueur en France. Il est précisé que son stockage dans une base de données est également interdit. Article disponible en ligne à l'adresse Article disponible en ligne à l'adresse https://www.cairn.info/revue-l-annee-psychologique1-2009-2-page-333.htm Découvrir le sommaire de ce numéro, suivre la revue par email, s'abonner... Flashez ce QR Code pour accéder à la page de ce numéro sur Cairn.info.

Journal of Comparative Psychology, 2001

Although the study of imitation in animals can be traced at least as far back as Thorndike (1898)... more Although the study of imitation in animals can be traced at least as far back as Thorndike (1898), research on imitative learning in animals has seen renewed interest in recent years (Galef, 1998; Heyes & Galef, 1996; Zentall & Galef, 1988). This resurgence of research interest can be attributed to the development of procedures that distinguish imitative learning from other socially mediated and attentional behavior (e.g., contagion, social facilitation, local and stimulus enhancement, and object movement reenactment). Stimulus enhancement is one of the most persistent alternative accounts of what has been presumed to be imitative learning. Stimulus enhancement may be present when the facilitation of acquisition by the observer can be attributed to the increased attention to a stimulus or manipulandum resulting from the behavior of a demonstrator (see Denny, Clos, & Bell, 1988; Galef, 1988; Zentall & Levine, 1972). An appropriate means of controlling for such enhancement was originally reported by Dawson and Foss (1965; see also Galef, Manzig, & Field, 1986). In this design, known as the two-action method, one of two different means of achieving the same outcome is demonstrated to an observer by a member of the same species (a conspecific). The two-action method does not require the inclusion of a social facilitation control group to determine the effect of the mere presence of another animal on the acquisition of the target behavior, because all the groups observe a demonstrator. In addition, the two-action method controls for possible stimulus enhancement effects, because all the observers are exposed to demonstrators that interact with the same manipulandum (i.e., increased attention to the manipulandum should affect all animals equally). Recently, the two-action method has been used to demonstrate imitative learning in Japanese quail (Coturnix japonica; Akins & Zentall, 1996, 1998; Dorrance & Zentall, 2001), as well as in pigeons (Zentall, Sutton, & Sherburne, 1996). In these studies, birds that had observed demonstrators pecking at a treadle (a small platform near floor level) for food reward mostly pecked the treadle when given access to it, whereas birds that had observed demonstrators stepping on the treadle mostly stepped on the treadle. The two-action method has been criticized, however, on the grounds that birds may naturally step on the treadle in this apparatus, just as they might scratch the ground while foraging for food. Thus, the stepping response may not be acquired through imitation but could occur naturally through trial and error learning. Furthermore, the birds that 275

Current Directions in Psychological Science, 2013

Human gambling generally involves suboptimal choice because the expected return is usually less t... more Human gambling generally involves suboptimal choice because the expected return is usually less than the investment. We have found that animals, too, choose suboptimally under similar choice conditions. Pigeons, like human gamblers, show an impaired ability to objectively assess overall probabilities and amounts of reinforcement when a rare, high-value outcome (analogous to a jackpot in human gambling) is presented in the context of more frequently occurring losses. More specifically, pigeons prefer a low-probability, high-reward outcome over a guaranteed low-reward outcome with a higher overall value. Furthermore, manipulations assumed to increase impulsivity (pigeons maintained at higher levels of motivation for food and pigeons housed in individual cages) result in increased suboptimal choice. They do so presumably because they function to increase attraction to the signal for the low-probability, high-reward outcomes rather than consider the more global probability of reinforcem...