Papers by Victor M Navarro
sleep supports the consolidation of memory, and it has been proposed that this enhancing effect o... more sleep supports the consolidation of memory, and it has been proposed that this enhancing effect of sleep pertains in particular to memories which are encoded under control of prefrontal–hippocampal circuitry into an episodic memory system. Furthermore, repeated reactiva- tion and transformation of such memories during sleep are thought to promote the de-contextualization of these mem- ories. here, we aimed to establish a behavioral model for the study of such sleep-dependent system consolidation in rats, using a go/nogo conditional discrimination learning task known to essentially depend on prefrontal–hippocam- pal function. Different groups of rats were trained to crite- rion on this task and, then, subjected to 80-min retention intervals filled with spontaneous morning sleep, sleep dep- rivation, or spontaneous evening wakefulness. In a subse- quent test phase, the speed of relearning of the discrimina- tion task was examined as indicator of memory, whereby rats were either tested in the same context as during train- ing or in a different context. sleep promoted relearning of the conditional discrimination task, and this effect was similar for testing memory in the same or different context (p < 0.001). Independent of sleep and wakefulness during the retention interval, animals showed faster relearning when tested in the same context as during learning, com- pared with testing in a different context (p < 0.001). the benefitting effect of sleep on discrimination learning was primarily due to an enhancing effect on response suppres- sion during the nogo stimulus. We infer from these results that sleep enhances memory for inhibitory behavioral control in a generalized context-independent manner and thereby might eventually also contribute to the abstraction of schema-like representations.
Concept Learning Without Differential Reinforcement in Pigeons by Means of Contextual Cueing
How supervision is arranged can affect the way that humans learn concepts. Yet very little is kno... more How supervision is arranged can affect the way that humans learn concepts. Yet very little is known about the role that supervision plays in nonhuman concept learning. Prior research in pigeon concept learning has commonly used differential response–reinforcer procedures (involving high-level supervision) to support reliable discrimination and generalization involving from 4 to 16 concurrently presented photographic categories. In the present project, we used contextual cueing, a nondifferential reinforcement procedure (involving low-level supervision), to investigate concept learning in pigeons. We found that pigeons were faster to peck a target stimulus when 8 members from each of 4 categories of black-and-white photographs— dogs, trees, shoes, and keys— correctly cued its location than when they did not. This faster detection of the target also generalized to 4 untrained members from each of the 4 photographic categories. Our results thus pass the prime behavioral tests of conceptualization and suggest that high-level supervision is unnecessary to support concept learning in pigeons.
We trained six pigeons in a stagewise Multiple Necessary Cues (MNC) go/no-go task to document the... more We trained six pigeons in a stagewise Multiple Necessary Cues (MNC) go/no-go task to document the dynamics of discrimination learning involving increasingly complex visual stimuli. The compound stimuli were composed from four dimensions, each of which could assume either of two extreme values or their intermediate value: Shape, Size, Line Orientation, and Brightness. Starting with a stimulus composed entirely from intermediate values, we replaced those values with each of the two extreme dimensional values in four successive stages, thereby increasing the stimulus set from 2 in Stage 1 to 16 in Stage 4. In each stage, only one combination of values signaled food (S +), whereas the remaining combinations did not (S − s). We calculated the rate of pecking during the first 15 s of each stimulus presentation and, in any given stage, training continued until the rate of responding to all of the S − s was less than 20% of the rate of responding to the S +. All pigeons successfully acquired the final discrimination, suggesting that they attended to all of the dimensions relevant for the discrimination. We also repli-cated the key results of prior MNC studies: (1) the number of extreme dimensional values in each stage was positively related to the amount of training required for pigeons to acquire the discrimination; (2) attentional tradeoffs were most often observed when three or four dimensions were being trained; and (3) throughout training, the number of dimensional values in the S − s that differed from the S + was positively related to their discriminability from S + .
There is substantial evidence that drug-paired cues become associated with drug effects. From a P... more There is substantial evidence that drug-paired cues become associated with drug effects. From a Pavlo- vian perspective, these cues act as conditioned stimuli and elicit conditioned compensatory responses that contribute to drug tolerance. Here we report two experiments with rats in which we studied the extinction of the associative tolerance to the ataxic effect of ethanol. Experiment 1 evaluated whether changes in the temporal and physical contexts after extinction training provoke recovery of the extin- guished tolerance. The results showed successful extinction, spontaneous recovery and renewal of the extinguished tolerance, but no summation of renewal and spontaneous recovery. Experiment 2 evalu- ated whether using massive extinction trials and delivering extinction in multiple contexts attenuates the renewal effect. The results showed that both manipulations reduced renewal of the extinguished tol- erance to the ataxic effect of ethanol; however, these manipulations used in combination did not appear to be more effective in reducing recovery than each by itself. The present results may help guide further research that evaluates behavioral ploys to prevent the recovery of extinguished responses.
Stepwise Conceptualization in Pigeons
We explored the relation between concept learning and the number of training exemplars, programme... more We explored the relation between concept learning and the number of training exemplars, programmed in a stepwise fashion. Eight pigeons (Columba livia) were trained via differential food reinforcement to peck 1 of 2 simultaneously displayed color images: benign or malignant human breast tissue samples. In each session, only 1 exemplar from each category was trained. If the learning criterion was achieved in 1 session, then those 2 exemplars were discarded and 2 new exemplars were trained in the next session. For the consistent group the reinforced category (benign or malignant stimuli for different birds) was maintained throughout all 24 training pairs, but for the inconsistent group the reinforced category was pseudorandomly changed from pair to pair. Pigeons in the consistent group evidenced striking gains in accuracy during the 1st few trials of training on new pairs (exceeding 90% correct over Pairs 10–12), whereas pigeons in the inconsistent group evidenced reliably weaker gains in initial categorization accuracy (rising above only 70% correct after comparable training). Stepwise training involving as few as a dozen exemplars per category was thus sufficient to support robust concept learning in pigeons.
Pathologists and radiologists spend years acquiring and refining their medically essential visual... more Pathologists and radiologists spend years acquiring and refining their medically essential visual skills, so it is of considerable interest to understand how this process actually unfolds and what image features and properties are critical for accurate diagnostic performance. Key insights into human behavioral tasks can often be obtained by using appropriate animal models. We report here that pigeons (Columba livia)—which share many visual system properties with humans—can serve as promising surrogate observers of medical images, a capability not previously documented. The birds proved to have a remarkable ability to distinguish benign from malignant human breast histopathology after training with differential food reinforcement; even more importantly, the pigeons were able to generalize what they had learned when confronted with novel image sets. The birds’ histological accuracy, like that of humans, was modestly affected by the presence or absence of color as well as by degrees of image compression, but these impacts could be ameliorated with further training. Turning to radiology, the birds proved to be similarly capable of detecting cancer-relevant microcalcifications on mammogram images. However, when given a different (and for humans quite difficult) task—namely, classification of suspicious mammographic densities (masses)—the pigeons proved to be capable only of image memorization and were unable to successfully generalize when shown novel examples. The birds’ successes and difficulties suggest that pigeons are well-suited to help us better understand human medical image perception, and may also prove useful in performance assessment and development of medical imaging hardware, image processing, and image analysis tools.
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Papers by Victor M Navarro