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Zentall, T. R., & Sherburne, L. M. (1994). Role of differential sample responding in the differential outcomes effect involving delayed matching by pigeons. J Exp Psychol Anim Behav Process, 20(4), 390–401.
Abstract: The role of differential sample responding in the differential outcomes effect was examined. In Experiment 1, we trained pigeons on a one-to-many matching task with differential sample responding required. Differential outcomes were associated with samples and comparisons, with comparisons only, or with neither samples nor comparisons. Slopes of delay functions for trials with pecked versus nonpecked samples suggested use of a single-code-default strategy in the nondifferential-outcomes group but not in the differential-outcomes groups. In Experiment 2, differential sample responding and differential outcomes were manipulated independently. Again, there were significant differences in the relative slopes of the delay functions. Results suggest that differential outcomes exert their effect independently of differential sample responding.
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Zentall, T. R., & Sherburne, L. M. (1994). Transfer of value from S+ to S- in a simultaneous discrimination. J Exp Psychol Anim Behav Process, 20(2), 176–183.
Abstract: Value transfer theory has been proposed to account for transitive inference effects (L. V. Fersen, C. D. L. Wynne, J. D. Delius, & J. E. R. Staddon, 1991), in which following training on 4 simultaneous discriminations (A+B-, B+C-, C+D-, D+E-) pigeons show a preference for B over D. According to this theory, some of the value of reinforcement acquired by each S+ transfers to the S-. In the transitive inference experiment, C (associated with both reward and nonreward) can transfer less value to D than A (associated only with reward) can transfer to B. Support for value transfer theory was demonstrated in 2 experiments in which an S- presented in the context of a stimulus to which responses were always reinforced (S+) was preferred over an S- presented in the context of a stimulus to which responses were sometimes reinforced (S +/-).
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Roper, K. L., & Zentall, T. R. (1993). Directed forgetting in animals. Psychol Bull, 113(3), 513–532.
Abstract: Directed-forgetting research with animals suggests that animals show disrupted test performance only under certain conditions. Important variables are (a) whether during training, the cue to forget (F cue) signals nonreward (i.e., that the trial is over) versus reward (i.e., that reinforcement can be obtained) and (b) given that reinforcement can be obtained on F-cue trials, whether the post-F-cue response pattern is compatible with the baseline memory task. It is proposed that some findings of directed forgetting can be attributed to trained response biases, whereas others may be attributable perhaps to frustration-produced interference. It is suggested that directed forgetting in animals should be studied using procedures similar to those used to study directed forgetting in humans. This can be accomplished by presenting, within a trial, both to-be-remembered and to-be-forgotten material.
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Zentall, T. R., Kaiser, D. H., Clement, T. S., Weaver, J. E., & Campbell, G. (2000). Presence/absence-sample matching by pigeons: divergent retention functions may result from the similarity of behavior during the absence sample and the retention interval. J Exp Psychol Anim Behav Process, 26(3), 294–304.
Abstract: Divergent choose-absence retention functions typically found in pigeons following presence/absence-sample matching have been attributed to the development of a single-code/default coding strategy. However, such effects may result from adventitious differential responding to the samples. In Experiment 1, retention functions were divergent only when differential sample responding could serve as the basis for comparison choice. In Experiment 2, when pecking did not occur during the retention interval, a choose-absence bias was found, but when pecking occurred during the retention interval, a choose-presence bias resulted. In Experiment 3, positive transfer was found when a stimulus associated with the absence of pecking replaced the absence sample but not when a stimulus associated with pecking replaced the presence sample. Thus, presence/absence-sample matching may not encourage the development of a single-code/default coding strategy in pigeons.
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Zentall, T. R. (1999). Support for a theory of memory for event duration must distinguish between test-trial ambiguity and actual memory loss. J Exp Anal Behav, 72(3), 467–472.
Abstract: Staddon and Higa's (1999) trace-strength theory of timing and memory for event duration can account for pigeons' bias to “choose short” when retention intervals are introduced and to “choose long” when, following training with a fixed retention interval, retention intervals are shortened. However, it does not account for the failure of pigeons to choose short when the intertrial interval is distinct from the retention interval. That finding suggests that stimulus generalization (or ambiguity) between the intertrial interval and the retention interval may result in an effect that has been attributed to memory loss. Such artifacts must be eliminated before a theory of memory for event duration can be adequately tested.
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Clement, T. S., Weaver, J. E., Sherburne, L. M., & Zentall, T. R. (1998). Simultaneous discrimination learning in pigeons: value of S- affects the relative value of its associated S+. Q J Exp Psychol B, 51(4), 363–378.
Abstract: 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+.
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Zentall, T. R., Clement, T. S., Bhatt, R. S., & Allen, J. (2001). Episodic-like memory in pigeons. Psychon Bull Rev, 8(4), 685–690.
Abstract: It has been proposed that memory for personal experiences (episodic memory, rather than semantic memory) relies on the conscious review of past experience and thus is unique to humans. In an attempt to demonstrate episodic-like memory in animals, we first trained pigeons to respond to the (nonverbal) question “Did you just peck or did you just refrain from pecking?” by training them on a symbolic matching task with differential responding required to the two line-orientation samples and reinforcing the choice of a red comparison if they had pecked and the choice of a green comparison if they had not pecked. Then, in Experiment 1, after providing the conditions for (but not requiring) the pigeons to peck at one new stimulus (a yellow hue) but not at another (a blue hue), we tested them with the new hue stimuli and the red and green comparisons. In Experiment 2, we tested the pigeons with novel stimuli (a circle, which they spontaneously pecked, and a dark response key, which they did not peck) and the red and green comparisons. In both experiments, pigeons chose the comparison appropriate to the response made to the test stimulus. Thus, the pigeons demonstrated that they could remember specific details about their past experiences, a result consistent with the notion that they have the capacity for forming episodic-like memories.
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Clement, T. S., & Zentall, T. R. (2002). Second-order contrast based on the expectation of effort and reinforcement. J Exp Psychol Anim Behav Process, 28(1), 64–74.
Abstract: Pigeons prefer signals for reinforcement that require greater effort (or time) to obtain over those that require less effort to obtain (T. S. Clement, J. Feltus, D. H. Kaiser, & T. R. Zentall, 2000). Preference was attributed to contrast (or to the relatively greater improvement in conditions) produced by the appearance of the signal when it was preceded by greater effort. In Experiment 1, the authors of the present study demonstrated that the expectation of greater effort was sufficient to produce such a preference (a second-order contrast effect). In Experiments 2 and 3, low versus high probability of reinforcement was substituted for high versus low effort, respectively, with similar results. In Experiment 3, the authors found that the stimulus preference could be attributed to positive contrast (when the discriminative stimuli represented an improvement in the probability of reinforcement) and perhaps also negative contrast (when the discriminative stimuli represented reduction in the probability of reinforcement).
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Zentall, T. R., Weaver, J. E., & Clement, T. S. (2004). Pigeons group time intervals according to their relative duration. Psychon Bull Rev, 11(1), 113–117.
Abstract: In the present research, we asked whether pigeons tended to judge time intervals not only in terms of their absolute value but also relative to a duration from which they must be discriminated (i.e., longer or shorter). Pigeons were trained on two independent temporal discriminations. In one discrimination, sample durations of 2 and 8 sec were associated with, for example, red and green hue comparisons, respectively, and in the other discrimination, sample durations of 4 and 16 sec were associated with vertical and horizontal line comparisons, respectively. If pigeons are trained on a temporal discrimination and tested with intermediate durations, the subjective midpoint typically occurs close to the geometric mean of the two trained values. The 4- and 8-sec values were selected to be the geometric mean of the two values in the other discrimination. When a 4-sec test sample was presented with the comparisons from the 2- and 8-sec discrimination, the pigeons preferred the comparison associated with the shorter sample. Similarly, when an 8-sec test sample was presented with the comparisons from the 4- and 16-sec discrimination, the pigeons preferred the comparison associated with the longer sample. Thus, a relative grouping effect was found. That is, durations that should have produced indifferent choice were influenced by their relative durations (shorter than or longer than the alternative) during training.
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Zentall, T. R., Clement, T. S., & Weaver, J. E. (2003). Symmetry training in pigeons can produce functional equivalences. Psychon Bull Rev, 10(2), 387–391.
Abstract: Functional stimulus equivalence has been demonstrated using a transfer of training design with matching-to-sample training in which two sample stimuli are associated with the same comparison stimulus (A-B, C-B; many-to-one matching). Equivalence is shown by training a new association (A-D) and demonstrating the presence of an emergent relation (C-D). In the present experiment, we show that symmetry training, in which a bidirectional association is trained between two stimuli (A-B, B-A, using successive stimulus presentations followed by reinforcement), can also produce functional equivalence using a transfer of training design (i.e., train B-C, test A-C). The results suggest that training pigeons in the substitutability of two stimuli may be sufficient to produce functional stimulus equivalence between them. The results also have implications for the development of an emergent transitive relation, because training on A-B and B-C relations results in the emergence of an untrained A-C relation, if B-A training also is provided.
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