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1.
Within-trial contrast has been proposed as a mechanism underlying preferences for stimuli that follow relatively more aversive
events over stimuli that follow less aversive events. In this study, we manipulated deprivation level to test within-trial
contrast predictions. In Experiment 1, pigeons encountered two discriminative stimuli, one presented when they were deprived
and the other when they were prefed. When later given a choice between the two stimuli, pigeons strongly preferred the stimulus
encountered when deprived, independently of their deprivation level at test. In Experiment 2, pigeons learned two simultaneous
discriminations, one when deprived and the other when prefed. Here, subsequent tests between the two S+ or the two S− stimuli revealed no consistent preferences. These contrasting findings suggest that differential aversiveness is necessary
but not sufficient to induce preferences via within-trial contrast. 相似文献
2.
Four experiments were performed to determine the stimulus characteristics that favor the development of conditional stimulus control in the single reversal paradigm with pigeon subjects. In Experiment 1, pigeons were trained on a successive discrimination between tone frequencies ranging from 350 to 3500 Hz in a particular houselight context condition (houselight-on or -off). The subjects then were trained on the reversal of the tone discrimination in the alternative context. Subsequent tone-frequency generalization testing in the two contexts indicated that they had failed to gain conditional control over the pigeons’ discriminative performance. Such control was obtained in Experiment 2, in which the two problems were alternated daily for 32 sessions of training. The gradients then peaked at the appropriate S+ value in each context. In Experiment 3, the key colors (blue vs. red) served as contexts while pigeons learned a successive discrimination in which the discriminative cues were houselight-on versus houselight-off conditions. This was followed by a reversal of the discrimination in the alternative key-color context condition. The key colors were effective conditional cues in this situation. In a previous experiment (Thomas, McKelvie, & Mah, 1985), key color had been ineffective as a conditional cue when the discriminative cues were lines superimposed on the colored background. In Experiment 4, key color was effective when the color and lines were presented on a single key as in the earlier experiment, but were sequenced such that the onset of the key color preceded and then overlapped the presentation of the lines. We concluded that conditional discriminations are easiest for pigeons when visual cues are used, but the conditional and discriminative cues must be presented in such a way that they do not combine to form a psychological compound. 相似文献
3.
Minimal procedures for the demonstration of transitive inference (TI) in animals have involved the training of four simultaneous discriminations: for example, A+B?, B+C?, C+D?, and D+E?, followed by the demonstration of a preference for B over D on test trials. In Experiment 1, we found that TI in pigeons can be found with successive training involving A+B?, B+C?, A+C?, C+D?, D+E?, C+E?, and A+E?. In Experiment 2, we found that demonstration of TI did not require inclusion of experience with the nonadjacent stimulus pairs (A+C?, C+E?, A+E?). Experiment 3 provided a test of value transfer theory (VTT; Fersen, Wynne, Delius, & Staddon, 1991). When pigeons were trained with stimulus pairs that did not permit the transitive ordering of stimuli, but did permit the differential transfer of value (e.g., A+B?, C?E+, C+D?, & A+E?), preference for B over D was still found. Analyses of the relation between direct experiences with reinforced and nonreinforced responding and stimulus preferences on test trials failed to support a reinforcement-history account of TI. 相似文献
4.
Zentall TR 《Learning & behavior》2008,36(1):19-22
Within-trial contrast occurs when a discriminative stimulus that is preceded by a relatively aversive event is preferred over
another that is preceded by a less aversive event. Recent failures to replicate (Arantes & Grace, 2008; Vasconcelos, Urcuioli,
á Lionello-DeNolf, 2007) may allow us to identify factors that may be responsible. In the case of Vasconcelos et al., it is
likely that insufficient training was provided (often 35–65 sessions are required). In the case of Arantes and Grace (Experiment
2), these pigeons had been involved in prior experiments involving lean schedules of reinforcement, and we find that prior
experience with lean (relatively aversive) schedules appears to reduce the presumed aversiveness of the many-peck requirement,
thus obviating the contrast effect. Finally, in the case of Vasconcelos and Urcuioli (2008), although the contrast effect
with a simultaneous discrimination was not reliable, it was not reliably smaller than with a successive discrimination that
did show a reliable effect, and the contrast effect was also similar in magnitude to a reliable effect reported by Kacelnik
and Marsh (2002). Thus, although there have been several failures to replicate the original effects reported by Clement, Feltus,
Kaiser, and Zentall (2000), insufficient training, prior history with lean schedules of reinforcement, and low statistical
power may have been responsible for those failures. 相似文献
5.
Charlotte Bonardi 《Learning & behavior》1996,24(3):277-289
In Experiment 1, pigeons were trained on two feature-positive discriminations. A transfer test examined whether the feature from one discrimination enhanced responding to the target from the other. Transfer was obtained, but it was incomplete; the feature produced less responding to the transfer target than to its own. Experiments 2 and 3 examined whether this attenuation of responding was the product of generalization decrement induced by the novel combination of feature and target on transfer trials. Birds were trained on a pair of pseudo-occasion-setting discriminations in which each target was reinforced whether or not it was preceded by its feature. In a subsequent test, there was no loss of responding when novel combinations of features and targets were introduced; on the contrary, responding was, if anything, enhanced in this condition. This suggests that imperfect transfer is not due to generalization decrement but to the fact that an occasion setter is specific to its target stimulus. 相似文献
6.
During simultaneous discrimination training, there is evidence that some of the value of the S+ transfers to the S?. When the value of the S+ is altered outside the context of the simultaneous discrimination, two very different predictions are made concerning its effect on its S?, depending on whether one views the S+ as an occasion setter or as a stimulus capable of transferring value. In four experiments, pigeons were trained with two similar simultaneous discriminations, A+B? and C+D?, and two single-stimulus trial types, A and C, (in which A always had greater nominal value than C). According to value transfer theory, on test trials, B should always be preferred over D, because B and D should be affected by the net values of A and C, respectively. According to an occasion setting account, however, D should be preferred over B because the presence of D signals a higher probability of reinforcement for responding to C than when C is alone, and/or the presence of B signals a lower probability of reinforcement for responding to A than when A is alone. In all four experiments, the pigeons preferred B over D, a result consistent with value transfer theory. Thus, an S? can acquire value from an S+ even when that value is conditioned in a “context” different from that of the simultaneous discrimination. 相似文献
7.
In Experiment 1, four groups of rats were initially trained on a discrimination which established a stimulus as a signal for reinforcement. That signal was then presented during subsequent partial reinforcement training in a way that could potentially interfere with retrieval of the memory of nonreinforcement (SN) on the preceding trial either because (1) thestorage and retrieval contexts for SN were different (retrieval failure hypothesis), or (2) the memory of reinforcement produced by the signal acted as a competing memory (competing memory hypothesis). Experiment 1 supported the competing memory hypothesis. In Experiment 2, we investigated the effect of stimulus change on the capacity of the context to retrieve a competing memory of a temporally remote reinforcement event with which the context was strongly associated. Retrieval of a competing memory was impaired by differences between the storage and retrieval contexts in a manner analogous to the effect of context on retrieval of a reinforcement event memory from an immediately preceding trial. 相似文献
8.
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. 相似文献
9.
Zentall (2008) challenges Arantes and Grace’s (2008) failure to replicate Clement, Feltus, Kaiser, and Zentall (2000) by suggesting
that our results may have been due to insufficient training or to subjects’ experimental histories, and that our results are
actually consistent with those of Clement et al. when examined closely. On the contrary, our pigeons received more training
than Clement et al.’s did, and when an overall measure of preference on test trials was calculated, independent of the effect
of initiating event that we reported, there was no evidence of preference for the stimulus preceded by the greater response
requirement in our data. Although there have now been two unsuccessful attempts to replicate Clement et al.’s work ethic effect,
there is evidence that in some situations, the value of a stimulus, as assessed by transfer tests, varies inversely with the
context of reinforcement. It is important to look for convergent results using other procedures and transfer tests, such as
resistance to change, to identify the principles that determine when contrast manipulations affect value and when they do
not. 相似文献
10.
Delayed simple discriminations are typically retained more accurately over longer delays by pigeons than are delayed conditional discriminations (e.g., Honig & Wasserman, 1981). In two experiments, we investigated the extent to which trial outcomes contribute to this difference by comparing performances when all trials ended with food reinforcement versus when only half of the trials did. Experiment 1 showed that when food was presented on all trials, contingent upon either pecking or not pecking the test stimulus, levels of retention and rates of forgetting were comparable for these two tasks. By contrast, Experiment 2 showed better retention of delayed simple than delayed conditional discriminations when half of the trials ended with food and the other half in extinction. Furthermore, delayed simple discriminations were retained more accurately with food versus no-food outcomes than with food at the end of every trial, whereas the reverse was true for delayed conditional discriminations. These findings indicate that retention differences between these tasks are another instance of the differential outcomes effect. 相似文献
11.
In Experiment 1, six groups of pigeons (n=8) were tested for wavelength generalization either immediately or 24 h after learning a successive discrimination, with 550 nm reinforced and a black vertical line extinguished. The groups differed in the stimulus present during single stimulus pretraining, which was 550 nm (pretrain S+), the vertical Une (pretrain S?), or a neutral dim white light (pretrain Sn), respectively. The three immediate generalization gradients were steep and indistinguishable, reflecting only the immediately preceding discrimination training condition. The three delay gradients were flatter, with the flattening particularly marked in the pretrain S? group. This was interpreted as proactive interference (PI) resulting from the memory that both the 550-nm and the line stimuli had previously been reinforced. In Experiment 2, two (TD) groups of pigeons (n=16) were given single stimulus training with a 555-nm keylight followed by eight sessions of discrimination training with two line angles, then one session of non-differential (ND) training with the same two lines, and then a wavelength generalization test either immediately or after a 24-h delay. Two other (hold) groups (n=16) received similar training, except for the TD Une angle training sessions, in these hold groups, the wavelength gradient was flatter in a delayed test; in the TD groups it was steeper, indicating PI from the prior TD training. These two experiments suggest that the “attentional sets,” which purportedly result from TD and ND training, may fruitfully be viewed as target memories subject to the principles of interference theory. 相似文献
12.
The effects of identical context on pattern recognition by pigeons for outline drawings of faces were investigated by training
pigeons to identify (Experiment 1) and categorize (Experiment 2) these stimuli according to the orientation of the mouth—an
upright U shape representing a smiling mouth or an inverted U shape representing a sad mouth. These target stimuli were presented
alone (Pair 1), with three dots in a triangular orientation to represent a nose and eyes (Pair 2), and with the face pattern
surrounded by an oval (Pair 3). In Experiment 1, the pigeons trained with Pair 1 were most accurate, those trained with Pair
2 were less so, and those trained with Pair 3 failed to acquire the discrimination within eighty 100-trial sessions. The same
ordering was found in Experiment 2 for pigeons trained on the three pairs simultaneously. The authors suggest that a contrasting
finding in humans, the face superiority effect, might be due to a gain in discriminability resulting from recognition of the
pattern as a face. An exemplar model of information processing that excludes linguistic coding accounts for the present results. 相似文献
13.
Two experiments assessed the degree to which Pavlovian facilitators were interchangeable with instrumental discriminative stimuli (Sds). In Experiment 1, rats were trained in a Pavlovian paradigm in which one stimulus (i.e., a facilitator) signaled the reinforcement of another stimulus (i.e., a target). Next, the rats were given instrumental discrimination training in which an Sd signaled the reinforcement of barpressing. A transfer test then assessed the capacity of the Pavlovian facilitator to promote barpressing. The results showed that the facilitator promoted significant barpressing, both when it was presented alone and when it was presented in compound with the Sd. Reliable transfer was not obtained with a “pseudofacilitator” control stimulus that, during training, was uninformative about the reinforcement of its target. Experiment 2 showed that a stimulus trained as an instrumental Sd reliably augmented responding to a stimulus previously trained as a target in a Pavlovian facilitation paradigm. A “pseudo-Sd” that, during training, was uninformative about the reinforcement of barpressing failed to promote such transfer. These results show that Pavlovian facilitators and instrumental Sds are interchangeable to a significant degree, and suggest that facilitators and Sds may act via similar mechanisms. 相似文献
14.
Jacky Emmerton 《Learning & behavior》1998,26(3):243-256
Two experiments are described in which pigeons were trained in a simultaneous conditioning procedure to discriminate small arrays of dots that differed in numerosity. The birds successfully learned to choose the array of each pair that contained fewer dots when these choices were reinforced and choices of the array with more dots led to timeout. For the majority of numerosity values tested, discrimination performance for a fixed S+ value was better when the numerical difference between S+ and S-values was larger rather than smaller. This effect was seen in the first experiment when the numerical difference value was shifted between training trials and novel test trials. In the second experiment, too, performance level depended on the size of the numerosity difference when the birds were concurrently trained with two difference values that varied across trials within sessions. However, discrimination accuracy was influenced secondarily by variations in the density, or interdot spacing, of the stimulus arrays. In order to explain the latter finding, it is suggested that a tendency to “scan” a lowdensity array incompletely might alter the probability of accepting it as the smaller numerosity (S+) stimulus. This would increase error rates with S? arrays in which the dots are more widely spaced. 相似文献
15.
An attempt was madeto manipulate the strength of internal stimulus representations by exposing pigeons to brief delays between sample offset and comparison onset in a delayed conditional discrimination. In Experiment 1, pigeons were first trained on delayed conditional discrimination with either short (0.5-sec) delays or no delays. When delays were increased by 2.0 sec, birds trained with a delay performed at a higher level than did birds trained with no delays. In Experiment 2, subjects were first trained on a delayed simple discrimination. Following a circle stimulus, responses to a white key were reinforced; however, following a dot stimulus, responses to the white key were not reinforced. The pigeons were then trained on a delayed conditional discrimination involving hue samples and line-orientation comparisons with differential outcomes. Choice of vertical following red yielded food; choice of horizontal following green yielded no food. Mixed delays were then introduced to birds in Group Delay, whereas birds in the control group received overtraining. When tested on a delayed simple discrimination with hue stimuli (red and green initial stimuli followed by white response stimulus), pigeons in Group Delay tended to perform at a higher level than did birds in the control group (i.e., although the birds in both groups responded more following red than following green, birds in Group Delay did this to a greater extent than did birds in the control group). Thus, experience with delays appears to strengthen stimulus representations established during training. 相似文献
16.
In three experiments, pigeons were trained to discriminate between uniform arrays of two elements that differed in color, form, or size. They were then tested with arrays that contained different proportions of the two elements on these dimensions. In all cases, orderly discrimination gradients reflected these proportions. The discrimination readily transferred to new arrays with similar stimuli, but with different total numbers of elements. In Experiment 4, the pigeons were taught to discriminate between two groups of categorical stimuli: pictures of birds and pictures of flowers. A test with different proportions of each again produced a gradient based on relative numerosity. Experiment 5 demonstrated transfer of stimulus control on the numerosity dimension when pigeons were trained with one set of instances from two categories, and then were tested with new instances from the same categories. 相似文献
17.
In four experiments, rats were trained on different patterning discriminations before being tested with compounds composed of novel combinations of the trained stimuli. In Experiment 1, rats were trained on a negative-patterning schedule (A+ B+ AB-) intermixed with reinforced presentations of a second compound (CD+). On a subsequent test, the rats responded more to two novel compounds, AC and BD, than to A and B, but less than to CD. In Experiment 2, rats were trained on two concurrent negative-patterning discriminations (A+ B+ AB-, C+ D+ CD-). On test, they responded more to AC and BD than to AB and CD, but less than to the single stimuli. In Experiment 3, rats were trained on two concurrent positive-patterning discriminations (A-B- AB+, C- D- CD+). On test, their response rates to AC and BD were not different from the response rates to the trained compounds (AB and CD). Finally, in Experiment 4, rats were trained on a positive- and negative-patterning discrimination concurrently. Once again, on test, response rates to AC and BD were not different from responding on reinforced trials of the trained discriminations (A+, B+, and CD+). We discuss the implications of these findings for elemental and configural models of stimulus representation. 相似文献
18.
Two groups of pigeons were trained with a go/no-go procedure to discriminate video images of conspecifics based on the individuals or else on their actions. Both groups showed rapid acquisition, and the discrimination transferred to new scenes in Experiment 1 and to static scenes in Experiment 2. In Experiment 3, experimentally naive pigeons were trained to discriminate video images of particular birds showing different actions. Transfer to novel scenes, including a new bird and a new motion, revealed the dominance of motion as a cue to discriminate video images. In Experiment 4, the pigeons trained to discriminate video scenes of 2 pigeons showing a variety of activities successfully recognized these stimuli regardless of whether the video was played forward or backward, and transferred the discrimination to still scenes. The findings suggest that pigeons’ discrimination of video images is primarily based on information that is invariant across static and dynamic conditions. 相似文献
19.
Pigeons trained on a conditional event-duration discrimination typically “choose short” when retention intervals are inserted between samples and comparisons. In two experiments, we tested the hypothesis that this effect results from ambiguity produced by the similarity of the novel retention intervals and the familiar intertrial interval by training pigeons with retention intervals from the outset and, for one group, in addition, making retention intervals distinctive from the intertrial intervals. In Experiment 1, when the retention intervals (0–4 sec) were not distinctive from the intertrial intervals, the pigeons did not show a clear choose-short effect even when extended retention intervals (8 sec) were introduced. When the retention intervals were distinctive, the pigeons showed a choose-long effect (they appeared to time through the retention interval), but it was relatively weak until the retention intervals were extended to 8 sec. In Experiment 2, when pigeons were discouraged from timing through the retention intervals by making the intertrial intervals and retention intervals salient distinct events and using long (up to 16-sec) retention intervals in training, parallel retention functions were found. It appears that when ambiguity is removed, forgetting by pigeons does not occur by the process of subjective shortening. These experiments suggest that the accurate interpretation of results of animal memory research using differential-duration samples must consider the novelty of the retention intervals on test trials as well as their similarity to other trial events. 相似文献
20.
Pigeons were trained with one eye covered on each of two types of visual discriminations. They then were tested for interocular transfer with the previously covered eye. Transfer was shown by every pigeon trained on a simultaneous discrimination, while lack of transfer was shown by thesesame pigeons when trained on a spatial conditional (successive) discrimination. As opposed to the pigeon, animals with a larger proportion of ipsilateral (uncrossed) retinal fibers (e.g., cats) do show transfer of both discrimination problems. This difference in the decussation of the optic pathways may be a critical variable in interocular transfer in vertebrates. Furthermore, these studies demonstrate that interocular transfer in the pigeon depends upon the experimental paradigm. 相似文献