Retroactive inhibition without intentional new learning: Some comment on the elicitation hypothesis

Two groups of subjects learned a list of paired-associates. Subsequently, an interpolated phase was introduced that did not require the acquisition of a new PA-list. The experimental group had to fulfill a number of little tasks with respect to the first terms of the previously learned list, whereas the control group did the task with words which were not on that list. In two experiments it was shown that when the retention of the learned associates was tested, the experimental group suffered more from forgetting than the control group. It is concluded that new learning is not a prerequisite in the induction of RI. The position of the elicitation hypothesis of Two Factor theory is critically discussed and the evocative disuse hypothesis is presented as an alternative conception with respect to the phenomenon of interference.     

Conceptual similarity promotes generalization of higher order fear learning

We tested the hypothesis that conceptual similarity promotes generalization of conditioned fear. Using a sensory preconditioning procedure, three groups of subjects learned an association between two cues that were conceptually similar, unrelated, or mismatched. Next, one of the cues was paired with a shock. The other cue was then reintroduced to test for fear generalization, as measured by the skin conductance response. Results showed enhanced fear generalization that correlated with trait anxiety levels in the group that learned an association between conceptually similar stimuli. These findings suggest that conceptual representations of conditional stimuli influence human fear learning processes.     

Analysis of the pavlovian properties of signals for punishment

Rats learned to suppress lever pressing in the presence of a compound stimulus that signalled either response-independent shock (conditioned suppression) or response-dependent shock (punishment). Suppression to one element of this compound was blocked if the other element had previously signalled the same contingency as that holding in the presence of the compound. Two experiments, however, failed to find significant evidence of blocking if the pretrained element had signalled conditioned suppression and the compound signalled a punishment contingency. On the other hand, if one stimulus signalled punishment of one response it was able to block the acquisition of control by the second stimulus when the compound signalled punishment of a different response. Finally, although animals showed no suppression to one element of a compound signalling conditioned suppression if the other had previously signalled punishment, this apparent blocking effect concealed that what they learned was that the added element signalled the cancellation of the instrumental contingency. These results provide little support for the view that stimuli signalling punishment contingencies suppress responding in whole or in part by virtue of their Pavlovian relation to shock.     

Visual discrimination learning and transfer in rats with hippocampal lesions

Two experiments were performed on rats with hippocampal brain damage and on a control group with neocortical lesions. In the first experiment the hippocampal group learned a difficult visual discrimination as promptly as the controls, and neither group was subsequently impaired by adding relevant or irrelevant background cues to the original stimuli. In the second experiment the animals learned a simultaneous visual discrimination in which the stimuli differed in both brightness and orientation. The hippocampal group was impaired relative to the controls on acquisition, and showed poorer transfer to stimuli differing only in brightness or orientation. The results are incompatible with the hypothesis which attempts to explain the effects of hippocampal damage by a widespread reduction in sensory gating, but they are consistent with a more restricted version of the same hypothesis.     

Selective learning enabled by intention to learn in sequence learning

This study investigated whether a target sequence that people intend to learn is learned selectively when it is interleaved with another (non-target) sequence. Three experiments used a serial reaction time task in which different spatial and color stimuli occurred alternately. Each of the two interleaved sequences had structural regularity. Participants in an intentional learning group were instructed to learn the target (spatial) sequence whereas those in an incidental learning group were not. In Experiments 1 and 2 spatial and color sequences were correlated. Results showed that the intentional group learned the spatial sequence better than the incidental group and learned it independently of the color sequence, whereas the incidental group learned the two sequences as a combined sequence. In Experiment 3 the sequences were uncorrelated. Results showed that the intentional group was no longer superior in learning the spatial sequence. Findings indicate that the intention to learn a target sequence enables selective learning of it only when it is correlated with a non-target sequence.     

Socially mediated learning in male Betta splendens

Seven experiments showed that in the absence of social stimulation male Siamese fighting fish would approach any of several visual and spatial cues that had previously been paired with the animals' mirror images. These findings demonstrate that learned modifications of swimming mediated by social stimuli are possible in Bettas. The present results also suggest that territorial defense in some teleosts may, in part, be mediated by the association of social cues with visual and spatial stimuli.     

Partial reinforcement and breadth of learning

Two experiments on partial reinforcement were undertaken to test predictions made by a two process model of discrimination learning. In the first experiment rats were trained on a discrimination involving two relevant cues: one group (C) was trained on a 100: o schedule, the other (P) on a 50:0 schedule. Both groups were then given transfer tests with the two cues presented individually; finally all animals were extinguished on the original training stimuli and on the single cue stimuli. During extinction there was a negative correlation between the number of correct responses made by individual subjects of Group C to each single cue; whereas the correlation was positive for subjects of Group P. The second experiment employed basically the same design, but subjects were trained with seven relevant cues. The results of transfer tests showed that subjects of Group P learned to attach the correct response to many more cues than subjects of Group C. This suggests that the breadth of learning is greater under partial than under consistent reinforcement. The results were predicted by the model of discrimination learning under test.     

Contextual dependencies in predictive learning

Two experiments assessed contextual dependencies in a predictive-learning task. Subjects learned to associate each of four pictorial stimuli with the occurrence or non-occurrence of a specific outcome. Each of these stimuli, the intentional stimuli, was presented against one of two different visual (Experiment 1) or auditory (Experiment 2) context stimuli. These context stimuli were incidental: subjects were not explicitly instructed to pay any attention to them and each of them in isolation was not predictive of the outcome. During acquisition and testing, subjects expressed the expected relationship between intentional stimulus and outcome by an appropriate key press. At test, intentional stimuli were presented either with the same contextual stimulus as also present during acquisition (same trials), or with the other one (switched trials). The response latency was slower on switched trials than on same trials in each experiment, a result extending previous findings on the effect of environmental contextual stimuli on task performance. Results are discussed in the framework of contextual occasion setting and habituation to contextual stimuli.     

Generalizing prosodic patterns by a non-vocal learning mammal

Prosody, a salient aspect of speech that includes rhythm and intonation, has been shown to help infants acquire some aspects of syntax. Recent studies have shown that birds of two vocal learning species are able to categorize human speech stimuli based on prosody. In the current study, we found that the non-vocal learning rat could also discriminate human speech stimuli based on prosody. Not only that, but rats were able to generalize to novel stimuli they had not been trained with, which suggests that they had not simply memorized the properties of individual stimuli, but learned a prosodic rule. When tested with stimuli with either one or three out of the four prosodic cues removed, the rats did poorly, suggesting that all cues were necessary for the rats to solve the task. This result is in contrast to results with humans and budgerigars, both of which had previously been studied using the same paradigm. Humans and budgerigars both learned the task and generalized to novel items, but were also able to solve the task with some of the cues removed. In conclusion, rats appear to have some of the perceptual abilities necessary to generalize prosodic patterns, in a similar though not identical way to the vocal learning species that have been studied.     

Contextual dependencies in predictive learning

Two experiments assessed contextual dependencies in a predictive-learning task. Subjects learned to associate each of four pictorial stimuli with the occurrence or non-occurrence of a specific outcome. Each of these stimuli, the intentional stimuli, was presented against one of two different visual (Experiment 1) or auditory (Experiment 2) context stimuli. These context stimuli were incidental: subjects were not explicitly instructed to pay any attention to them and each of them in isolation was not predictive of the outcome. During acquisition and testing, subjects expressed the expected relationship between intentional stimulus and outcome by an appropriate key press. At test, intentional stimuli were presented either with the same contextual stimulus as also present during acquisition (same trials), or with the other one (switched trials). The response latency was slower on switched trials than on same trials in each experiment, a result extending previous findings on the effect of environmental contextual stimuli on task performance. Results are discussed in the framework of contextual occasion setting and habituation to contextual stimuli.     

Implicit learning of new verbal associations

Implicit learning of a series of new verbal associations was studied in four experiments. The first two experiments demonstrated that learning of a repeating sequence of verbal stimuli may occur without awareness, but only when the stimulus-response mapping requires an attention-demanding activity: Subjects who were unaware of the sequence learned when instructed to categorize the stimuli, but not when instructed simply to read them. However, in both situations, unaware subjects performed no better than untrained control subjects in expressing their knowledge of the sequence explicitly. In Experiments 3 and 4, subjects showed implicit learning when the task involved either motor responses to verbal stimuli or verbal responses to spatially arranged stimuli. These findings are discussed in terms of the conditions under which implicit learning can be obtained. First, they demonstrate implicit learning of a set of new associations in the verbal domain. Second, the data suggest that attention is important in implicit learning. Finally, the degree of interitem organization that is familiar preexperimentally seems to partially determine the amount of implicit learning.     

The impact of motor responses on serial-pattern learning

Subjects are able to learn even very complex serial patterns in serial-reaction-time tasks. The investigation of the learning processes behind this phenomenon has yielded contradictory results. Some studies have come to the conclusion the subjects had learned the sequence of stimuli. Other studies have assumed that the sequence of responses had been learned or a combination of both stimuli and responses. The present experiments stress the impact of motor responses on serial-pattern learning. The subjects had to respond to serial targets that were presented within a matrix of distractors. The position of each target could be predicted from the identity and position of the previous target. If the subjects were to learn this pattern, they would be able to speed up the search for the target and give faster responses. The results indicated that the relation between the target identity and the position of the next target was acquired much better by those subjects who had to respond to each target with a special motor response. If the same response was required for the relevant targets, knowledge of the rule was somewhat fragmentary. To explain these results, mechanisms of motor learning and motor planning are discussed. It is assumed that learning of the rules occurs if the position changes appear to be effects of different motor responses.     

The generality of learned helplessness in the rat

Two experiments were simultaneously conducted in which two different groups of 40 rats each were exposed to one of two different stressors. In both experiments half the subjects were pretreated with shock, half with underwater exposure. For each pretreatment stressor, half the subjects were allowed to escape, the other half were not. The experiments differed in the test task used. Approximately 24 hr after pretreatment, one-half the subjects from each pretreatment group received 20 water-escape trials in an underwater maze, the other half received 20 shock-escape trials in a two-way shuttle box. The subjects in each of the inescapable pretreatment conditions were slower to escape in the subsequent shock-escape and water-escape tasks when compared with subjects in the corresponding escapable pretreatment condition. The “learned helplessness” effect appeared to be no smaller when aversive stimuli were changed between pretreatment and test than when they remained the same.     

Test-potentiated learning of motor sequences

We investigated effects of retrieving body movements from memory on subsequent re-encoding of these movements (i.e., test-potentiated learning). In Experiment 1, participants first learned to perform 12 sequential finger movements as responses to letter stimuli. Eight of these movements then had to be recalled in response to their stimuli (initial test). Subsequently, learning trials were repeated for four of the previously to-be-retrieved movements as well as the previously not-to-be-retrieved movements. Restudy benefited from prior retrieval. In a final test, again requiring motoric recall in response to letter stimuli, performance was better for restudied items that were previously cued for retrieval as compared to items that had been restudied without prior retrieval. However, no such indirect testing benefit occurred when initial and final testing formats were incongruent, that is, when participants had to recall the stimuli in response to movements as cues at the final test. In Experiment 2, we replicated the finding of test-potentiated learning with a different design, manipulating initial-testing status between participants.     

Socially mediated learning in male Betta splendens. III: Rapid acquisitions

In four experiments with male Siamese fighting fish, the classical conditioning of visual/spatial cues with elicitors of aggression was demonstrated. These studies show that this type of socially mediated learning is more rapidly conditioned than was previously known. One 15-min training session is adequate to condition a preference for those cues that had recently been paired with conspecific images. Finally, behavior occurring during acquisition, in the presence of aggression-eliciting cues, was uncorrelated with the magnitude of the learned preferences that were assayed during extinction tests and in the absence of social stimuli.     

Augmentation of eating following a signal for feeding in rats

Previous studies have shown that a CS for feeding produces increases in some measures of excitation, but effects on other behaviors have not been examined. Two experiments examined effects on eating. In each experiment, one group of rats was presented with a CS preceding feeding, while control groups had no anticipatory signal. Ss with signaled feeding learned to eat more than control Ss, and their body weights were relatively higher. These results indicate that conditioned incentive stimuli may have broader effects than have classically been attributed to them. It is also suggested that learned factors may mediate the effects of deprivation operations on eating and play a significant part in the regulation of feeding.     

Luminous targets: Visibility fluctuations modified by similar verbal responses

Ss reported visibility fluctuations in a luminous target consisting of small, medium, and large circles. Each S had previously learned a response to each of the three circles. The experimental group learned two words which were free associates of each other and a third unrelated word. The control group learned three unrelated words. Concurrent visibility for the pair of circles associated with related words was greater than for the pairs associated with unrelated words. Thus word associations influence perception of stimuli for which the words are responses.     

Active avoidance behavior following archistriatal lesions in pigeons.

Experiment 1 examined the performance of 10 pigeons, 5 with bilateral medial archistriatal lesions and 5 sham-operated controls, in the acquisition and maintnenance of a discrete-press avoidance response. The archistriatal subjects had longer response latencies and never attained the level of performance achieved by the controls. In Experiment 2 eight pigeons learned a treadle-press response to avoid or escape shock on a signaled free-operant schedule. After 17 daily sessions four subjects received bilateral lesions in the medial archistriatum, and four received control lesions in the neostriatum. After recovery from surgery, all subjects were returned to the experimental procedure. Avoidance of those subjects with archistriatal lesions was impaired relative to the postoperative level while that of the control group was unchanged. These results are interpreted in the light of earlier experiments showing reduced escape and avoidance behavior both in order avian species and in mammals with lesions in the amygdala, to which the archistriatum is considered homologous.     

Right or wrong, familiar or novel in pictorial list discrimination learning

The interaction between nonassociative learning (presentation frequencies) and associative learning (reinforcement rates) in stimulus discrimination performance was investigated. Subjects were taught to discriminate lists of visual pattern pairs. When they chose the stimulus designated as right they were symbolically rewarded and when they chose the stimulus designated as wrong they were symbolically penalised. Subjects first learned one list and then another list. For a "right" group the pairs of the second list consisted of right stimuli from the first list and of novel wrong stimuli. For a "wrong" group it was the other way round. The right group transferred some discriminatory performance from the first to the second list while the control and wrong groups initially only performed near chance with the second list. When the first list involved wrong stimuli presented twice as frequently as right stimuli, the wrong group exhibited a better transfer than the right group. In a final experiment subjects learned lists which consisted of frequent right stimuli paired with scarce wrong stimuli and frequent wrong stimuli paired with scarce right stimuli. In later test trials these stimuli were shown in new combinations and additionally combined with novel stimuli. Subjects preferred to choose the most rewarded stimuli and to avoid the most penalised stimuli when the test pairs included at least one frequent stimulus. With scarce/scarce or scarce/novel stimulus combinations they performed less well or even chose randomly. A simple mathematical model that ascribes stimulus choices to a Cartesian combination of stimulus frequency and stimulus value succeeds in matching all these results with satisfactory precision.     

Inhibitory stimulus control following errorless discrimination learning

Three generalization procedures were used to investigate inhibitory stimulus control following discrimination learning with few errors. Three groups of pigeons acquired a discrimination between a green stimulus (the positive stimulus) and a vertical or horizontal line (the negative stimulus) through differential autoshaping followed by multiple schedule presentation of the two stimuli with gradually increasing stimulus durations. Genereralization testing was along a line-tilt continuum. For one group, the test involved a resistance-to-reinforcement procedure in which responses to all line tilts were reinforced on a variable-interval schedule. For a second group, also tested with the resistance-to-reinforcement procedure, the lines were superimposed on the green field that formerly served as the positive stimulus. A third group was tested in extinction with the combined stimuli. Control groups had no discrimination training but responding to green was nondifferentially reinforced. The control subjects responded more to all line tilts during testing than did the comparable experimental subjects, indicating that the negative stimulus had become an inhibitory stimulus. Both resistance-to-reinforcement groups revealed inhibitory gradients around the negative stimulus, but the gradient for the extinction group was relatively flat. These data are consistent with others that modify Terrace's early conclusion concerning the failure of inhibition to develop during errorless training.