Journal of Experimental Psychology-Animal Learning and Cognition最新文献

Exposure to complex checkerboards (comprising a common background, e.g., X, with unique features, e.g., A-D, that are placed in particular locations on the background) improves discrimination between them (perceptual learning). Such stimuli have been used previously to probe human perceptual learning but these studies leave open the question of whether the improvement in discrimination is based on the content or location of the unique stimuli. Experiment 1 suggests that perceptual learning produced by exposure to AX and BX transferred to stimuli that had new unique features (e.g., C, D) in the position that had been occupied by A and B during exposure. However, there was no transfer to stimuli that retained A and B as the unique features but moved them to a different location on the background. Experiment 2 replicated the key features of Experiment 1, that is, no transfer of exposure learning based on content but perfect transfer of exposure learning based on location using a design which allowed for independent tests of location- and content-based performance. In both the experiments reported here, superior discrimination between similar stimuli on the basis of exposure can be explained entirely by learning where to look, with no independent effect of learning about particular stimulus features. These results directly challenge the interpretation of practically all prior experiments using the same type of design and stimuli.

In the conditioned magazine approach paradigm, rats are exposed to a contingent relationship between a conditioned stimulus (CS) and the delivery of food (the unconditioned stimulus, US). As the rats learn the CS-US association, they make frequent anticipatory head entries into the food magazine (the conditioned response, CR) during the CS. Conventionally, this is considered to be a Pavlovian paradigm because food is contingent on the CS and not on the performance of CRs during the CS. However, because magazine entries during the CS are reliably followed by food, the increase in frequency of those responses may involve adventitious ("superstitious") instrumental conditioning. The existing evidence, from experiments using an omission schedule to eliminate the possibility of instrumental conditioning (B. J. Farwell & J. J. Ayres, 1979, Stimulus-reinforcer and response-reinforcer relations in the control of conditioned appetitive headpoking (goal tracking) in rats. Learning and Motivation, 10, 295-312; P. C. Holland, 1979, Differential effects of omission contingencies on various components of Pavlovian appetitive conditioned responding in rats. Journal of Experimental Psychology: Animal Behavior Processes, 5, 178-193), is ambiguous: rats acquire magazine CRs despite the omission schedule, demonstrating that the response does not depend on instrumental conditioning, but the response rate is greatly depressed compared with that of rats trained on a yoked schedule, consistent with a contribution from instrumental conditioning under normal (nonomission) schedules. Here we describe experiments in which rats were trained on feature-positive or feature-negative type discriminations between trials that were reinforced on an omission schedule versus trials reinforced on a yoked schedule. The experiments show that the difference in responding between omission and yoked schedules is due to suppression of responding under the omission schedule rather than an elevation of responding under the yoked schedule. We conclude that magazine responses during the CS are largely or entirely Pavlovian CRs.

Participants in 2 experiments classified face stimuli into 2 categories determined by the gender of the faces. Although the category rule was simple, the stimuli, created by morphing male and female faces, made the explicit identification of the rule difficult. Participants were classified as rule users or nonusers depending on whether they explicitly identified the gender rule on a postexperiment questionnaire. Nonusers displayed a generalization decrement to new category exemplars that were more obviously male and female but less similar to the trained exemplars. Rule users, instead, generalized their category judgments perfectly to new category members. However, when an exception to the rule was introduced, generalization decrement for stimuli related to the exception was evident in both groups. All participants displayed a near-perfect ability to reverse their category judgments, regardless of whether learning occurred in the presence or absence of the explicit gender rule. The results highlight a distinction between rule- and feature-based category learning but show that both processes are subject to cognitive control.

Previous research has demonstrated that nontool-using primates are capable of sophisticated motor planning for a single action. The present study extends this work by asking whether monkeys are capable of planning a sequence of repetitive motor actions to accommodate a task demand. We presented tamarins with a tape measure baited with a food reward at near or far distances and measured their manual intergrasp distances as they reeled in the food. In Condition 1, subjects viewed the reward as they pulled, whereas in Condition 2, they received no visual feedback during pulling. Across both experiments, we found that the intergrasp distance in Near trials was significantly smaller than in Far trials, an effect that was demonstrated even during the first two pulls of each trial. These results suggest that tamarins prospectively scale their intergrasp distances in accordance with the distance to the goal. These findings provide further support for the lengthy evolutionary history of sophisticated motor planning abilities in primates.

Strong interest exists in developing a rodent model of visual cognition to conduct research into the neural mechanisms of visual categorization. Yet, doubt remains as to whether rats perform visual categorization tasks as do humans and nonhuman primates. Here, we trained eight rats on two visual categorization tasks using photographs of eight objects from each of four basic-level categories: chairs, flowers, cars, and humans. In Experiment 1, rats learned to categorize chairs versus flowers; in Experiment 2, rats learned to categorize cars versus humans. After rats learned each discrimination, we tested them with eight novel pictures from each of the categories. The rats performed at reliably above-chance levels during these generalization tests. To determine which dimension(s) of the stimuli controlled the rats' behavior, we conducted regression analyses using several image dimensions. The chair versus flower discrimination was mainly controlled by the convexity of the stimuli, whereas the car versus human discrimination was mainly controlled by the aspect ratio of the stimuli. These results demonstrate that rats can categorize complex visual objects using shape-based properties of photographs.

In two experiments rats were trained to find one of two submerged platforms that were located in diagonally opposite corners-the correct corners-of a rectangular pool. Additional training was given to endow two different landmarks with excitatory and inhibitory properties, by using them to indicate where a platform was or was not located in either a rectangular (Experiment 1) or a square pool (Experiment 2). Subsequent test trials, with the platforms removed from the pool, revealed that placing the excitatory landmark in each of the four corners of the rectangle resulted in more time being spent in the correct corners than when the four corners contained inhibitory landmarks. This result is contrary to predictions derived from a choice rule for spatial behavior proposed by Miller and Shettleworth (2007).

In two experiments we investigated the role of hierarchical S-(R-O) associations, as opposed to associative alternatives, in solving biconditional discrimination problems in rats. Using lesions of posterior dorsomedial striatum known to attenuate R-O associative learning, and lesions of the dorsolateral striatum that attenuate S-R learning, we found that whereas the lesions affecting R-O learning abolished biconditional discrimination, lesions of dorsolateral striatum did not (Experiment 1). Furthermore, in Experiment 2, we found, using a more challenging discrimination protocol, that dorsolateral striatal lesions actually enhanced biconditional discrimination learning. These results provide evidence that hierarchical S-(R-O) associations influence instrumental discrimination learning and compete with S-R associations for control of performance.

This study examined the effects of previous outcomes on subsequent choices in a probabilistic-choice task. Twenty-four rats were trained to choose between a certain outcome (1 or 3 pellets) versus an uncertain outcome (3 or 9 pellets), delivered with a probability of .1, .33, .67, and .9 in different phases. Uncertain outcome choices increased with the probability of uncertain food. Additionally, uncertain choices increased with the probability of uncertain food following both certain-choice outcomes and unrewarded uncertain choices. However, following uncertain-choice food outcomes, there was a tendency to choose the uncertain outcome in all cases, indicating that the rats continued to "gamble" after successful uncertain choices, regardless of the overall probability or magnitude of food. A subsequent manipulation, in which the probability of uncertain food varied within each session as a function of the previous uncertain outcome, examined how the previous outcome and probability of uncertain food affected choice in a dynamic environment. Uncertain-choice behavior increased with the probability of uncertain food. The rats exhibited increased sensitivity to probability changes and a greater degree of win-stay/lose-shift behavior than in the static phase. Simulations of two sequential choice models were performed to explore the possible mechanisms of reward value computations. The simulation results supported an exponentially decaying value function that updated as a function of trial (rather than time). These results emphasize the importance of analyzing global and local factors in choice behavior and suggest avenues for the future development of sequential-choice models.

In 3 human predictive learning experiments, we investigated whether the allocation of attention can come under the control of contextual stimuli. In each experiment, participants initially received a conditional discrimination for which one set of cues was trained as relevant in Context 1 and irrelevant in Context 2, and another set was relevant in Context 2 and irrelevant in Context 1. For Experiments 1 and 2, we observed that a second discrimination based on cues that had previously been trained as relevant in Context 1 during the conditional discrimination was acquired more rapidly in Context 1 than in Context 2. Experiment 3 revealed a similar outcome when new stimuli from the original dimensions were used in the test stage. Our results support the view that the associability of a stimulus can be controlled by the stimuli that accompany it.