Showing papers in "Learning & Behavior in 2009"

The propositional approach to associative learning as an alternative for association formation models.

Abstract: Associative learning effects can be defined as changes in behavior that are due to relations between events in the world. Most often, these effects are explained in terms of the formation of unqualified associations in memory. I describe an alternative theoretical explanation, according to which associative learning effects are the result of the nonautomatic generation and evaluation of propositions about relations between events. This idea is supported by many studies showing that associative learning effects are determined not only by the direct experience of events but also by prior knowledge, instructions, intervention, and deductive reasoning. Moreover, evidence supports the assumption that associative learning effects depend on nonautomatic processes. Whereas a propositional approach thus offers many new insights, questions can be raised about what the idea of association formation adds to our understanding of associative learning.

Behavioral momentum and relapse of extinguished operant responding.

Abstract: Previous experiments on behavioral momentum have shown that relative resistance to extinction of operant behavior in the presence of a stimulus depends on the rate of reinforcement associated with that stimulus, even if some of those reinforcers occur independently of the behavior. We present three experiments examining whether the rate of reinforcement in the presence of a stimulus similarly modulates the relative relapse of operant behavior produced by reinstatement, resurgence, and renewal paradigms. During baseline conditions, pigeons responded for food reinforcement on variable-interval 120-sec schedules in alternating periods of exposure to two stimuli arranged by a multiple schedule. Additional response-independent food presentations were also delivered in the presence of one of the multiple-schedule stimuli. Consistent with previous research, baseline response rates were lower in the presence of the stimulus with the added response-independent reinforcement, and relative resistance to extinction was greater in the presence of that stimulus. In addition, following extinction, the relative relapse of responding produced by reinstatement, resurgence, and renewal paradigms was greater in the presence of the stimulus associated with the higher rate of reinforcement. We suggest that a model of extinction from behavioral momentum theory may be useful for understanding these results.

The search for symmetry: 25 years in review

Abstract: It has been 25 years since the publication of Sidman et al.’s (1982) report on the search for symmetry in nonhuman animals. They attributed their nonhuman subjects’ failure to the absence of some critical experiences (e.g., exemplar training, control of location variables, and generalized identity matching). Since then, species ranging from rats to chimpanzees have been tested on symmetry, and the results have been equivocal. Twenty-four investigations of symmetry in nonhumans are reviewed to determine whether the underlying factors first addressed by Sidman et al. (1982) have been verified and whether new factors have been identified. The emergent picture shows that the standard procedures as typically implemented on a three-key apparatus are insufficient by themselves to produce emergent symmetry in nonhumans. Recent successful demonstrations of symmetry in sea lions and pigeons have clarified certain important stimulus control variables (i.e., select and reject control) and suggest avenues for future research. Reliable symmetry may be achievable with nonhumans if training and test procedures that encourage compatible stimulus-control topographies and relations are designed.

Spacing extinction trials alleviates renewal and spontaneous recovery

Abstract: Studies of extinction in classical conditioning situations can reveal techniques that maximize the effectiveness of exposure-based behavior therapies. In three experiments, we investigated the effect of varying the intertrial interval during an extinction treatment in a fear-conditioning preparation with rats as subjects. In Experiment 1, we found less fear at test (i.e., more effective extinction) when extinction trials were widely spaced, relative to intermediate or massed extinction trials. In Experiment 2, we used an ABA renewal procedure and observed that spaced trials attenuated renewal of conditioned fear relative to massed trials. In Experiment 3, we used a similar design, but instead of changing the physical context at the time of testing, we interposed a retention interval after the extinction treatment to produce a change in the temporal context. The results showed less spontaneous recovery of fear after spaced than after massed extinction trials. These results suggest that extinction is more enduring when the extinction trials are spaced rather than massed. Although the benefits of spacing trials are small when there is no contextual change from extinction to testing, a change in either physical or temporal context following massed extinction trials leads to a recovery from extinction, which is reduced when the trials are spaced.

Preference for 50% reinforcement over 75% reinforcement by pigeons

Abstract: When pigeons are given a choice between an initial-link alternative that results in either a terminal-link stimulus correlated with 100% reinforcement or a stimulus correlated with 0% reinforcement (overall 50% reinforcement) and another initial-link alternative that always results in a terminal-link stimulus correlated with 100% reinforcement, some pigeons show a preference for the initial-link alternative correlated with 50% reinforcement. Using this procedure, in Experiment 1, we found a relatively modest preference for 100% over 50% reinforcement. In Experiment 2, we decreased the reinforcement density for the second initial-link alternative to 75% and found a significant preference for the 50% reinforcement initial-link alternative. It may be that this "maladaptive" behavior results from a positive contrast between the expectation of reinforcement correlated with the 50% reinforcement initial-link alternative and the terminal-link stimulus correlated with 100% reinforcement. But apparently, the complementary negative contrast does not develop between the expectation of reinforcement correlated with the 50% reinforcement initial-link alternative and the terminal-link stimulus correlated with 0% reinforcement that often follow. Such paradoxical choice may account for certain human appetitive risk-taking behavior (e.g., gambling) as well.

A learned flavor preference persists despite the extinction of conditioned hedonic reactions to the cue flavors.

Abstract: Learned flavor preferences can be strikingly persistent in the face of behavioral extinction. Harris, Shand, Carroll, and Westbrook (2004) suggested that this persistence may be due to flavor preference conditioning’s producing a long-lasting change in the hedonic response to the conditioned stimulus (CS+) flavor. In the present study, the CS+ flavor was presented in simultaneous compound with 16% sucrose, whereas the CS− flavor was presented with 2% sucrose. During subsequent two- and one-bottle tests, the CS+ and CS− flavors were presented in 2% sucrose. Hedonic reactions during training and test were assessed using an analysis of the microstructure of licking behavior. Conditioning resulted in greater consumption of the CS+ than of the CS− that did not extinguish over repeated two- and one-bottle tests. The mean lick cluster size was higher for the CS+ than for the CS− only on the first cycle of tests. Since lick cluster size can be used as an index of stimulus palatability, the present results indicate that although the hedonic reaction to the CSs did change, this was not maintained across repeated tests. Thus, changes in the hedonic response to the conditioned flavors cannot explain the resistance to the extinction of learned flavor preferences.

Varieties of perceptual learning

Abstract: Although most studies of perceptual learning in human participants have concentrated on the changes in perception assumed to be occurring, studies of nonhuman animals necessarily measure discrimination learning and generalization and remain agnostic on the question of whether changes in behavior reflect changes in perception. On the other hand, animal studies do make it easier to draw a distinction between supervised and unsupervised learning. Differential reinforcement will surely teach animals to attend to some features of a stimulus array rather than to others. But it is an open question as to whether such changes in attention underlie the enhanced discrimination seen after unreinforced exposure to such an array. I argue that most instances of unsupervised perceptual learning observed in animals (and at least some in human animals) are better explained by appeal to well-established principles and phenomena of associative learning theory: excitatory and inhibitory associations between stimulus elements, latent inhibition, and habituation.

The effects of rapid eye movement sleep deprivation and recovery on spatial reference memory of young rats.

Abstract: It is known that rapid eye movement (REM) sleep plays a crucial role in learning and memory. Previous studies have demonstrated that postlearning REM sleep deprivation (RSD) impairs memory consolidation. Most of these studies observed only the effects of RSD on learning and memory. In the present study, we not only investigated the impacts of 48-h RSD on the spatial reference memory of young rats in a Morris water maze, but also specifically examined whether an REM rebound for 24-48 h after 48-h RSD affected the maintenance of spatial reference memory. RSD was induced by the modified multiple platform method, and spatial reference memory was tested in a Morris water maze. The results demonstrated that, compared with the control groups, posttraining RSD for 48 h produced a significant impairment in the retention of acquired spatial reference memory, and the impairment continuously existed after 24 and 48 h of release from sleep deprivation, which indicates that REM sleep plays a critical role in reference memory maintenance and consolidation. Moreover, postlearning RSD may lead to a long-term impairment in the consolidation of newly acquired memories.

Roles of attention in perceptual learning from perspectives of psychophysics and animal learning

Abstract: The role of attention in perceptual learning has been a topic of controversy. Sensory psychophysicists/physiologists and animal learning psychologists have conducted numerous studies to examine this role; but because these two types of researchers use two very different lines of approach, their findings have never been effectively integrated. In the present article, we review studies from both lines and use exposure-based learning experiments to discuss the role of attention in perceptual learning. In addition, we propose a model in which exposure-based learning occurs only when a task-irrelevant feature is weak. We hope that this article will provide new insight into the role of attention in perceptual learning to the benefit of both sensory psychophysicists/physiologists and animal learning psychologists.

Perceptual learning and representational learning in humans and animals

Abstract: Traditionally, perceptual learning in humans and classical conditioning in animals have been considered as two very different research areas, with separate problems, paradigms, and explanations. However, a number of themes common to these fields of research emerge when they are approached from the more general concept of representational learning. To demonstrate this, I present results of several learning experiments with human adults and infants, exploring how internal representations of complex unknown visual patterns might emerge in the brain. I provide evidence that this learning cannot be captured fully by any simple pairwise associative learning scheme, but rather by a probabilistic inference process called Bayesian model averaging, in which the brain is assumed to formulate the most likely chunking/grouping of its previous experience into independent representational units. Such a generative model attempts to represent the entire world of stimuli with optimal ability to generalize to likely scenes in the future. I review the evidence showing that a similar philosophy and generative scheme of representation has successfully described a wide range of experimental data in the domain of classical conditioning in animals. These convergent findings suggest that statistical theories of representational learning might help to link human perceptual learning and animal classical conditioning results into a coherent framework.

A landmark blocks searching for a hidden platform in an environment with a distinctive shape after extended pretraining

Abstract: In the blocking phase of three experiments, rats had to find a submerged platform beneath a spherical landmark in one corner of a triangular pool. Prior to this treatment, they were required to find the platform relative to either a sphere above it (blocking groups) or a rod attached to it (control groups). The position of the platform changed from trial to trial for the initial training. The sphere did not restrict learning about the geometric cues provided by the triangular arena in the blocking phase when 12 sessions of initial training took place in either the triangular (Experiment 1) or a circular (Experiment 3) pool. Blocking was observed, however, after 24 sessions of initial training in either the triangular (Experiment 2) or the circular (Experiment 3) pool. Thus, blocking of geometric cues by a landmark is possible after extended initial training with the blocking cue.

Contextual control of first- and second-learned excitation and inhibition in equally ambiguous stimuli.

Abstract: In two three-phase experiments, rats received a final third excitatory (Experiment 1) or inhibitory (Experiment 2) phase of conditioning with a tone. The third phase came immediately prior to a test with the tone, either in the context where the tone was trained or in a different context. Groups differed in each experiment with respect to the first two phases. Rats in Groups EIE (Experiment 1) and EII (Experiment 2) received excitatory conditioning with the tone in Phase 1, followed by inhibitory conditioning with the tone. Rats in Groups IEE (Experiment 1) and IEI (Experiment 2) received inhibitory conditioning in Phase 1, followed by excitatory conditioning in Phase 2. Thus, the association being expressed in Phase 3 was consistent either with what was learned first about the stimuli or with what was learned second. Contrary to expectations, the association being expressed at the end of Phase 3, either excitatory or inhibitory, was affected by a context change, regardless of its consistency with what was learned first about the CS.

Reward contrast in delay and probability discounting.

Abstract: In this study, we examined whether reward contrast influences choice between delayed and probabilistic outcomes. Specifically, we predicted that the subjective value of an intermediate reward would seem relatively larger or smaller, respectively, if it followed choices involving a smaller or larger reward and would produce corresponding changes in rates of delay and probability discounting. In Experiment 1, subjects made choices about hypothetical $5,000 or $50 outcomes and then made choices about $500 outcomes. Delay-discounting rates for the $500 outcome were larger for Group $5,000 than for Group $50, whereas the opposite result was obtained for probability-discounting rates. In Experiment 2, we used a design that allowed for contrast effects to be assessed within subjects. Two groups made choices about delayed or probabilistic rewards. After completing question blocks in which the amount was $5,000 or $50, subjects responded to questions with an intermediate amount ($475/$525). For Group Delay, the present value of the intermediate reward was greater after the $50 block than after the $5,000 block, whereas the opposite was obtained for Group Probability. The results from both experiments confirmed the predictions of reward contrast and suggested that the subjective value of a monetary reward varies inversely with the prior reward amount.

Factors moderating blocking in human place learning: the role of task instructions.

Abstract: Cognitive map theory assumes that novel environmental information is automatically incorporated into existing cognitive maps as a function of exploration. Reports of blocking in place learning cast doubt on this claim. In these studies, subjects were first trained to find a place, using a set of landmarks (Set A). Then novel landmarks (Set B) were added for additional trials. Subsequent removal of the Set A landmarks showed that the novel landmarks alone were insufficient for successful navigation. We investigated whether instructing human subjects to explore the environment can moderate blocking. First, we demonstrated that blocking is absent in a computer implementation of the Morris water maze (MWM) in which subjects are instructed to explore. We then studied why others found blocking in a different MWM implementation, in which the task instructions did not suggest exploration. In experiments that faithfully replicated this MWM variant, we found that subjects did not acquire cognitive maps and that blocking was attenuated when instructions were provided that encouraged exploration. Together, these findings indicate that blocking in human place learning may reflect a performance deficit, not a learning deficit, and that instructions can moderate blocking. Our results thus support the automatic update assumption of cognitive map theory.

Attentional changes in blocking are not a consequence of lateral inhibition

Abstract: In three human causal learning experiments, we examined attentional modulation in the blocking task, in which participants typically learn little about a novel cue B when it is paired with a previously trained, predictive cue A. Evidence indicates that this blocking training led to a decrement in attention to the blocked cue B. The present experiments addressed whether this decrease in attention to the blocked cue could be better explained as being due to lateral inhibition from the pretrained cue A to the blocked cue B, or as a cue-specific property that is not conditional on the presence or absence of other stimuli. Strong effects of learned predictiveness were observed on participants’ causal judgments (Experiment 1) and choice behavior (Experiments 2 and 3). However, no evidence for lateral inhibitory processes emerged in any of the experiments, despite explicit attempts to maximize experimental sensitivity to this effect. The results are discussed in the context of formal models of the operation of attentional processes in human and animal learning.

Timing with opportunity cost: concurrent schedules of reinforcement improve peak timing.

Abstract: The temporal generalization gradient produced by the peak-interval (PI) procedure reflects behavior under the control of positive reinforcement for responding after the criterial time, but shows negligible discouragement for early responses. The lack of consequences for premature responding may affect estimates of timing accuracy and precision in the PI procedure. In two experiments, we sought to encourage more accurate timing in pigeons by establishing an opportunity cost for such responding. Concurrent ratio and interval schedules of reinforcement reduced the dispersion of keypecking around the target time. A sequence of three response-rate states (low-high-low) characterized performance in individual trials. Opportunity cost substantially reduced the mean and standard deviation of the duration of the middle-high state that typically enveloped the target time, indicating improved temporal acuity. We suggest a model as a first-order approximation to timing with opportunity cost.

Learning-related shifts in generalization gradients for complex sounds.

Abstract: Learning to discriminate stimuli can alter how one distinguishes related stimuli. For instance, training an individual to differentiate between two stimuli along a single dimension can alter how that individual generalizes learned responses. In this study, we examined the persistence of shifts in generalization gradients after training with sounds. University students were trained to differentiate two sounds that varied along a complex acoustic dimension. The students were subsequently tested on their ability to recognize a sound that they had experienced during training when it was presented among several novel sounds varying along this same dimension. Peak shift was observed in Experiment 1, in which generalization tests immediately followed training, and in Experiment 2, in which the tests were delayed by 24 h. These findings further support the universality of generalization processes across species, modalities, and levels of stimulus complexity. They also raise new questions about the mechanisms underlying learning-related shifts in generalization gradients. The sound stimuli from this study are available as .wav files from http://lb.psychonomic-journals.org/content/supplemental.

Extinction of conditioned inhibition: effects of different outcome continua.

Abstract: For some decades, failures to find extinction of inhibition through unpaired presentations of the inhibitor were taken as evidence against conceptualizing inhibition as the symmetrical counterpart of excitation. Recently, however, our group has demonstrated successful extinction of inhibition in human causal learning. In two experiments, we replicated and strengthened this finding by using an outcome continuum that could take on negative, neutral, or positive values. In contrast, the use of a dichotomous outcome continuum (either neutral or positive) resulted in the well-known nonoccurrence of extinction. Extinction of inhibition through the pairing of inhibitors with neutral outcomes was assessed by (1) comparing the (presumably) extinguished inhibitor with a second inhibitor that had not been presented with a neutral outcome in the extinction stage, and (2) demonstrating the course of extinction in participants’ predictions.

Individual differences: either relational learning or item-specific learning in a same/different task.

Abstract: Three pigeons were trained in a three-item simultaneous same/different task. Three of six stimulus combinations were not trained (untrained set) and were tested later. Following acquisition, the subjects were tested with novel stimuli, the untrained set, training-stimulus inversions, and object shape and color manipulations. There was no novel-stimulus transfer--that is, no abstract-concept learning. Two pigeons showed partial transfer to untrained pairs and good transfer to stimulus inversions, suggesting that they had learned the relationship between the stimuli. Lack of transfer by the third pigeon suggests item-specific learning. The somewhat surprising finding of relational learning by 2 pigeons with only six training pairs suggests restricted-domain relational learning that was controlled more by color than by shape features. Individual differences of item-specific learning by 1 pigeon and relational learning by 2 others demonstrate that this task can be learned in different ways and that relational learning can occur in the absence of novel-stimulus transfer.

Overshadowing and CS duration: counteraction and a reexamination of the role of within-compound associations in cue competition.

Abstract: In the present experiments, we examined the role of within-compound associations in the interaction of the overshadowing procedure with conditioned stimulus (CS) duration, using a conditioned suppression procedure with rats. In Experiment 1, we found that, with elemental reinforced training, conditioned suppression to the target stimulus decreased as CS duration increased (i.e., the CS duration effect), whereas, with compound reinforced training (i.e., the overshadowing procedure), conditioned suppression to the target stimulus increased as CS duration increased. In subsequent experiments, we replicated these findings with sensory preconditioning and demonstrated that extinction of the overshadowing stimulus results in retrospective revaluation with short CSs and in mediated extinction with long CSs. These results highlight the role of the duration of the stimulus in behavioral control. Moreover, these results illuminate one cause (the CS duration) of whether retrospective revaluation or mediated extinction will be observed.

Representations of single and compound stimuli in negative and positive patterning

Abstract: 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.

Symmetrical generalization decrements: configural stimulus processing in human contingency learning.

Abstract: Models of associative learning differ in their predictions concerning the symmetry of generalization decrements. Whereas Pearce’s (1994) configural model predicts the same response decrement after adding elements to and after removing elements from a previously trained stimulus, elemental models, such as the replaced elements model and Harris’s (2006) model, anticipate more of a decrement for removing than for adding elements. In three contingency learning experiments, we manipulated the motion and the spatial arrangement of colored dots in order to induce configural or elemental processing by perceptual grouping. The results reliably showed symmetrical decrements for the added and removed groups. The manipulations of the stimuli had no effect on stimulus processing. This is in line with Pearce’s configural model, but it is at variance with the elemental models and previous studies.

A differential-outcomes effect using hedonically nondifferential outcomes with delayed matching to sample by pigeons.

Abstract: When differential outcomes follow correct responses to each of two comparison stimuli in matching to sample, relative to the appropriate control condition, higher matching accuracy is typically found, especially when there is a delay between the sample and the comparison stimuli. In two experiments, we examined whether this differential-outcomes effect depends on using outcomes that differ in hedonic value (e.g., food vs. water). In Experiment 1, we found facilitated retention when a blue houselight followed correct responses to one comparison stimulus and a white houselight followed correct responses to the other, prior to nondifferential presentations of food. In Experiment 2, we found facilitated retention again when a blue houselight followed correct responses to one comparison stimulus and a tone followed correct responses to the other, prior to nondifferential presentations of food. The results of both experiments indicate that the differential-outcomes effect does not depend on a difference in hedonic value of the differential outcomes, and they suggest that outcome anticipations consisting of relatively arbitrary but differential stimulus representations can serve as cues for comparison choice.

Perceptual learning in human and nonhuman animals: a search for common ground.

Abstract: Perceptual learning has been extensively studied in both human and nonhuman animals, but the two lines of research have, for the most part, developed independently, addressing seemingly rather different issues by rather different methods It has been argued, however, that analysis of the disparate phenomena studied in experiments on perceptual learning reveals that in all the studies, the essential feature is that appropriate training allows behavior to come to be controlled by the unique features, rather than by the common features, of similar stimuli It has further been argued that experiments with nonhuman animals have established the existence of a range of learning processes that allow this to occur, and that these processes have general relevance, applying to humans as well as to animals

Generalization of causal efficacy judgments after evaluative learning.

Abstract: In three experiments, we examined the effect of response-outcome relations on human ratings of causal efficacy and demonstrated that such efficacy ratings transfer to novel situations through derived stimulus relations. Causal efficacy ratings were higher, and probability of an outcome given a response was lower, for a differential reinforcement of high rate schedule than for either a differential reinforcement of low rate schedule (Experiment 1) or a variable interval schedule (Experiment 2). In Experiment 3, we employed schedules that were equated for outcome probability and noted that ratings of causal efficacy and the rate of response were higher on a variable ratio than on a variable interval schedule. For participants in all three experiments, causal efficacy ratings transferred to the stimulus present during each schedule and generalized to novel stimuli through derived relations. The results corroborate the view that schedules are a determinant of both response rates and causal efficacy ratings. In addition, the novel demonstration of a mechanism of generalization of these ratings via derived relations has clinical implications.

What are association formation models

Abstract: In his presentation of the propositional account of associative learning, De Houwer (2009) argues that association formation models (AFMs) assume excitatory link representations and automatic learning processes. However, the application of AFMs to human causal and contingency learning has assumed propositional forms of representation, although excitatory link representations are also required to explain certain nonrational consequences of associative learning. Moreover, at least two of the AFMs that have been applied to human associative learning invoke processing with nonautomatic characteristics. In conclusion, the distinction between the propositional account and AFMs of associative learning lies not in the form of representations but in the specific details of the learning processes generating the associative representations.

Social effects on spatial choice in the radial arm maze

Abstract: Social memory was investigated in the context of a spatial working memory task. Pairs of rats were tested in an eight-arm radial maze. Under most conditions, there was a tendency to choose maze locations that had been visited earlier by the other rat. The possibility that this tendency is produced by common preferences for particular maze locations was ruled out. An opposite tendency to avoid visits to locations that had been visited earlier during the trial by another rat was found only when the maze location contained two pellets (rather than an undepletable supply), the rats' ability to see each other in the maze was restricted to the central arena, and the maze location had been previously visited by the focal rat. The amount of food available in maze locations did not otherwise modulate social influences on spatial choice. The results indicate that memory for a rat's own previous choices is combined with memory for the choices made by another rat.

Comparison of auditory and visual conditioning stimuli in delay eyeblink conditioning in healthy young adults.

Abstract: Classical eyeblink conditioning (EBC) has been widely used to probe cerebellar function in humans and nonhuman mammals. Although the neural pathways governing behavior in this task are well understood and fairly discrete, it remains unclear in the human literature how conditioned stimuli (CSs) of different modalities (e.g., visual and auditory) influence the exhibition of conditioned responses (CRs). In the present study, therefore, CRs to a visual CS and an auditory CS were examined with the single-cue delay EBC procedure. An initial experiment (N=61) was conducted to identify visual and auditory stimuli that had equal perceived intensities. Using these perceptually equivalent stimuli, a second group of 25 subjects completed auditory and visual EBC procedures in two testing sessions 5–8 days apart. Whereas the acquisition of CRs was similar between the CS modality conditions, the timing of the CRs differed such that earlier CR onset and peak latencies were associated with the visual CS. In addition, CR timing improved across testing sessions, as indicated by the later CR peak latencies exhibited during the second testing session, as compared with the first.

Counting absolute numbers of items, from 1 to 8, in pigeons

Abstract: Pigeons were trained in a forced choice task with four alternatives to categorize arrays consisting of 1, 3, 5, or 8 dots. Before the pigeons chose a comparison stimulus, they were required to peck each dot sequentially. A single peck to a dot, which was defined as an indicating response, changed the color of the dot so that it was differentiated from those that remained to be counted. The pigeons successfully learned to categorize the numerical arrays and then displayed transfer to novel arrays consisting of two, four, six, or seven dots, in a manner according to the order of 1 < 2 < 3 < 4 < 5 < 6 < 7 < 8. Subsequent tests revealed that the pigeons discriminated the stimuli by relying on the number of indicating responses. They also utilized multiple information (surface area, time, and other confounded events), but this was of minor significance, and after training, the pigeons were able to disregard these cues.

Effects of pretraining on acquisition of novel configural discriminations in human predictive learning.

Abstract: In two experiments, participants acquired one of two target configural discriminations (a biconditional or negative patterning discrimination) in a predictive learning task. In Experiment 1, participants were pretrained with either a configural or an elemental discrimination; in Experiment 2, they were pretrained with a configural discrimination, an elemental discrimination, or a control discrimination that was not expected to bias them toward elemental or configural processing. In both experiments, acquisition of the target configural discriminations was faster after configural pretraining than after elemental pretraining. In addition, the negative patterning discrimination was acquired faster than the biconditional discrimination. Finally, the results of Experiment 2 were more consistent with the notion that elemental pretraining hindered acquisition of the target discriminations than with the notion that configural pretraining enhanced their acquisition. Implications of these findings are discussed.