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At least 1,423 records · Page 79Linked to original sources
PubMed1986

Separation of taste-aversion-prone and taste-aversion-resistant rats through selective breeding: implications for individual differences in conditionability and aversion-therapy alcoholism treatment.

Both rats and alcoholic humans display considerable variability in acquisition of illness-induced consummatory aversions. Differential conditionability may be a significant modulator of outcome in alcoholics who elect taste aversion (TA) approaches to abstinence facilitation. This is a report of the ongoing development of rat strains suitable for studies of biological bases of individual differences in TA conditionability. Sprague-Dawley-derived rats have been selectively bred over seven generations as strong or weak learners of a cyclophosphamide-induced saccharin aversion. Efficiency of aversion acquisition is a selectable propensity, as indicated by progressively divergent strain separation that attained significance in the second selected generation. Subjects have also been studied with respect to shock-motivated environmental avoidance (SMEA), but efficiency of SMEA performance has not been a selection factor. Results have produced an unexpected trend across generations indicative of a within-strain reversal of TA and SMEA learning efficiency. Continuation of this reversal in subsequent generations could have important implications for studies of genetic contributions to different learning capacities and for the selection of biologically appropriate noxious stimuli for aversive therapy treatments of various target problems.

Alcoholism↗
PubMed2006

Perceptual recalibration in human sound localization: learning to remediate front-back reversals.

The efficacy of a sound localization training procedure that provided listeners with auditory, visual, and proprioceptive/vestibular feedback as to the correct sound-source position was evaluated using a virtual auditory display that used nonindividualized head-related transfer functions (HRTFs). Under these degraded stimulus conditions, in which the monaural spectral cues to sound-source direction were inappropriate, localization accuracy was initially poor with frequent front-back reversals (source localized to the incorrect front-back hemifield) for five of six listeners. Short periods of training (two 30-min sessions) were found to significantly reduce the rate of front-back reversal responses for four of five listeners that showed high initial reversal rates. Reversal rates remained unchanged for all listeners in a control group that did not participate in the training procedure. Because analyses of the HRTFs used in the display demonstrated a simple and robust front-back cue related to energy in the 3-7-kHz bandwidth, it is suggested that the reductions observed in reversal rates following the training procedure resulted from improved processing of this front-back cue, which is perhaps a form of rapid perceptual recalibration. Reversal rate reductions were found to generalize to untrained source locations, and persisted at least 4 months following the training procedure.

Acoustic Stimulation↗
PubMed1989

Children's expressions of spatial knowledge.

Different expressions of spatial knowledge were examined by having groups of first-, fourth-, and sixth-grade children perform model construction, verbal description, and route reversal tasks after they learned the correct path through a pedestrian maze. Age-related improvement was found in the rate of learning the maze and in the accuracy of verbal descriptions, suggesting that maze learning may be verbally mediated. All children performed well in sequencing intersections in the model but performed poorly in choosing path options in the model. Route reversal after learning was accurate and equivalent across groups. Overall, results suggest that both general and task-specific skills are involved in different products of spatial knowledge.

Child↗
PubMed1994

Preserved recognition memory for small sets, and impaired stimulus identification for large sets, following rhinal cortex ablations in monkeys.

Seven cynomolgus monkeys (Macaca fascicularis) performed a series of tasks designed to assess their visual memory and their ability to identify visual stimuli. Preoperatively they were trained and tested in delayed and simultaneous matching-to-sample, both with a large stimulus set and with a small stimulus set; there were approximately 500 million possible stimuli in the large set, which effectively means that stimuli were trial-unique with this set, while in the small set there were only four stimuli, which appeared repeatedly in every session of training with the small set. Three of the monkeys then had the cortex within and adjacent to the rhinal sulcus removed bilaterally, while the other four served as an unoperated control group. Postoperatively, the animals with ablation of the rhinal cortex showed severe impairment in delayed matching-to-sample with the large set. With the large set they were also impaired, however, in matching-to-sample with no delay between sample and test (0 s delay) and in simultaneous matching-to-sample, in which the sample and the two choice patterns were simultaneously present for inspection. The impairment in simultaneous matching-to-sample was particularly clear when the task was made more difficult by reducing the physical discriminability of the trial-unique stimuli. With the small set of four stimuli, the animals with rhinal cortex ablation were not significantly impaired in overall performance level in delayed matching-to-sample, though their level was on average below that of the normal control animals. The stimulus set was then further restricted, so that there were now only two stimuli used throughout; in this condition, the animals with rhinal cortex ablation performed delayed matching-to-sample without any suggestion of impairment, showing indistinguishable performance levels from those of the control animals over a range of forgetting intervals. Subsequently, the animals were trained in trial-unique non-matching-to-sample with 0 s delay, which required reversal of the matching-to-sample rule they had previously learned; animals with rhinal cortex ablation showed a clear impairment in this rule-reversal learning. The final experimental task was a concurrent discrimination learning task in which 20 pairs of stimuli were presented once per session; the animals with rhinal cortex ablation learned more slowly than the control animals on average, but the difference between the groups did not attain statistical significance.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2000

The effects of long-term ovariectomy and estrogen replacement therapy on learning and memory in monkeys (Macaca fascicularis).

This study determined the effects of estrogen loss and replacement therapy on learning and memory function in monkeys (Macaca fascicularis). The ability to learn, remember, and perform reversals of object discriminations and the accuracy on a spatial delayed response task were found to be comparable in young adult surgically menopausal monkeys receiving estrogen or placebo treatment for 5 or 16 months. Learning and memory abilities were comparable with baseline values following 2, 12, or 24 months of ovariectomy in monkeys. Pre- and postoperative injections of scopolamine in a subset of monkeys revealed only subtle increases in sensitivity on the delayed response task following ovariectomy. These observations in surgically menopausal monkeys have some parallels with those made in surgically menopausal women and suggest that, in the absence of other confounding factors, certain aspects of learning and memory may not be influenced by estrogen in primates.

Animals↗
PubMedDate not supplied

Postnatal cadmium exposure and longterm behavioral changes in the rat.

Although cadmium is a well known toxicant, its effects at subtoxic doses on behavior have rarely been investigated. The present study examined the longterm effect on levels of spontaneous locomotor activity and performance in a learning task resulting from postnatal exposure to cadmium. Sixty-four male Sprague-Dawley rat pups were divided into seven treatment and one vehicle control group. Treated animals were intubated with CdCl2 from the sixth to fifteenth day of life at doses ranging from 0.25 to 7.0 mg/kg body weight. Activity was quantified in tilt cages at forty-five days of age and performance in an appetitively motivated spatial discrimination task, with reversal, was assessed at between ninety and ninety-four days of age in a T-maze. A significant increase in spontaneous locomotor activity was observed in rats treated with 0.25 mg/kg of cadmium. In general, cadmium treated animals performed better than control subjects during learning and reversal learning trials. Possible hypotheses accounting for these results are discussed.

Animals↗
PubMed1982

Morphologic and behavioral effects of perinatal glucocorticoid administration.

Male rats were infused with one of two doses of dexamethasone or saline on day 4 of life. Body, whole brain, hippocampal, and cerebellar weights were obtained at 10, 20 and 150 days of age, and the ability of the rats to acquire and reverse a spatial discrimination task was assessed at 90 days of age. Body weights and brain weights were severely and permanently suppressed in the high dose group (100 mg/kg), resulting in a 20% decrement from saline-injected controls in adulthood. Low dose (1 mg/kg) animals were transiently slowed in body and brain growth, but differences from controls were no longer detectable at 60 days of age. Both high dose and low dose animals were significantly impaired in acquisition and reversal of a spatial learning task in an open field water maze, and exhibited deficits characteristically seen in animals with hippocampal damage. The animals' swimming performance per se was unimpaired. It appears that even transient interruption of normal interactive sequences of brain development by the alteration of post-natal neurogenesis or gliogenesis by glucocorticoids results in a permanent behavioral deficit.

Animals↗
PubMed1995

The role of instance retrieval in understanding complex concepts.

Conceptual combination studies have found that a property is often judged more salient in a complex concept than in its constituents. Medin and Shoben (1988), for example, found that metal is more typical than wooden of the simple concept SPOON, whereas wooden is more typical than metal of the complex concept LARGE SPOON. We explored the possibility that such typicality reversals reflect a process of instance retrieval; that is, subjects base their typicality judgments on previously stored instances of LARGE SPOON. This hypothesis predicts that performance in a task requiring typicality judgments and one requiring instance retrieval would be correlated. Three experiments supported this prediction. Experiment 1 provided typicality reversals for a set of concepts. Subjects in Experiments 2 and 3 described instances of the concepts. Aspects of these descriptions were used to predict the reversals. The correlation between predicted and obtained typicality reversals was substantial, and higher for concepts for which subjects retrieved many instances.

Adult↗
PubMed1987

Tactile discrimination learning deficits in Alzheimer's and Parkinson's diseases.

Neuropsychological mechanisms of dementia in Alzheimer's and Parkinson's diseases were compared using a tactile discrimination learning paradigm adopted from animal models. There were two components to the task: tactile original learning (TOL), which is sensitive to parietal lobe damage in nonhuman primates; and tactile reversal of original learning (TRL), a measure of perseveration. The patients with Alzheimer's disease were significantly impaired on TOL compared with demented patients with Parkinson's disease, even though both groups were equated for severity of dementia. On TRL, the patients with Alzheimer's disease and demented patients with Parkinson's disease were both significantly impaired, but the patients with Alzheimer's disease showed significantly more perseverative errors. The mechanisms underlying TOL and TRL deficits may serve to differentiate Alzheimer's from Parkinson's dementia, and may involve selective parietal system lesions.

Aged↗
PubMed1980

Reversible morphological alterations of cortical neurons in juvenile and adult hypothyroidism in the rat.

We have studied: (i) whether or not hypothyroidism induced experimentally in the adult rat affects the number and distribution of spines along the apical shaft of pyramidal cells from the visual cortex; and (ii) whether treatment with thyroid hormone would reverse such changes. Two experiments were performed. Experiment A involved the study of rats which were thyroidectomized (T) at 40 or at 120 days of age, killed at 120 and 220 days of age, respectively, data being compared to those of adequate sex and age-paired controls. Experiment B involved rats which were T at 40 days of age; they were subdivided into two groups, one of which was left untreated and the other received 0.2 microgram of thyroxine/100 g body weight/day for 25 days. Both groups were killed at 90 days of age. We found that: (i) T at 40 and at 120 days of age resulted in a decrease of the number of spines and a derangement of their distribution along the shaft, the observed changes being qualitatively comparable to those previously described for rats T at 10 days of age; and (ii) preliminary results from experiment B indicate that the observed changes in neuronal morphology might be reversible. It is suggested that age-independent and reversible alterations of learning capacity and electrocortical activity of hypothyroid rats might have age-independent and reversible morphological correlates at the level of the cortex.

Age Factors↗
PubMed1997

Task difficulty and the specificity of perceptual learning.

Practising simple visual tasks leads to a dramatic improvement in performing them. This learning is specific to the stimuli used for training. We show here that the degree of specificity depends on the difficulty of the training conditions. We find that the pattern of specificities maps onto the pattern of receptive field selectivities along the visual pathway. With easy conditions, learning generalizes across orientation and retinal position, matching the spatial generalization of higher visual areas. As task difficulty increases, learning becomes more specific with respect to both orientation and position, matching the fine spatial retinotopy exhibited by lower areas. Consequently, we enjoy the benefits of learning generalization when possible, and of fine grain but specific training when necessary. The dynamics of learning show a corresponding feature. Improvement begins with easy cases (when the subject is allowed long processing times) and only subsequently proceeds to harder cases. This learning cascade implies that easy conditions guide the learning of hard ones. Taken together, the specificity and dynamics suggest that learning proceeds as a countercurrent along the cortical hierarchy. Improvement begins at higher generalizing levels, which, in turn, direct harder-condition learning to the subdomain of their lower-level inputs. As predicted by this reverse hierarchy model, learning can be effective using only difficult trials, but on condition that learning onset has previously been enabled. A single prolonged presentation suffices to initiate learning. We call this single-encounter enabling effect 'eureka'.

Humans↗
PubMed2001

Effects of a flavor-placement reversal test after different modalities of taste aversion learning.

Taste aversion learning is induced through two different behavioral procedures: a short-term or concurrent (two-daily flavors) and a long-term or sequential (one-daily flavor) procedure. For the concurrent group of animals, two gustatory/olfactory stimuli are presented separately but at the same time on a daily basis. One is paired with simultaneous intragastric administration of hypertonic NaCl and the other with physiological saline. For the sequential group, the two stimuli are presented on alternate days, one of them followed by intragastric injection of the aversive stimulus and the other by saline, both after a delay of 15 min. The two groups learned the task, but when they were subjected to a flavor-placement reversal test only the sequential group was successful in achieving it. In a second experiment, three groups of animals had to learn concurrent or sequential discrimination tasks (with either simultaneous or delayed administration of the visceral stimulus) using only spatial/proprioceptive cues. The data show that none of the groups learned them under these conditions. The results are discussed in terms of the different modalities of learning. Short-term and long-term taste aversion learning are different in the anatomical structures involved, the number of trials required for acquisition and, as shown in this paper, flexibility.

Animals↗
PubMed2004

Successive reversal of concurrent discriminations by macaques (Macaca mulatta): proactive interference effects.

Rhesus monkeys received concurrent within-session training on eight, two-choice object pairs and then underwent successive reversals of these problems. Initially, reversals required about six times more training than acquisition with no improvement over seven successive reversals. Surprisingly, performance on these eight problems was unimpaired if they were embedded in different eight-problem tasks, thereby indicating a release from proactive interference. When the original eight problems again underwent successive reversal, no improvement was seen over seven reversals, although there was significantly less error-per-reversal than in the initial test. Subsequently, monkeys appeared to be developing a learning set for successive reversal because performance on successive reversal of eight novel problems was not different from that seen with the old familiar task. Set acquisition was confirmed when proficient reversal was eventually achieved on both old and new concurrent tasks. Thus, "concurrent reversal set" did develop, but it required arduous training to overcome proactive interference effects on memory. The ubiquitous influence of measurement context on organization of monkey memory was noted.

Animals↗