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PubMed1995

Abrupt luminance change pops out; abrupt color change does not.

The present studies investigated whether an isoluminant color change pops out, indicating that it can be detected preattentively in parallel. The results of Experiment 1 show that an abrupt color change presented on an equiluminant background does not pop out. However, when the color change is accompanied by a small luminance change, it does pop out. The results of Experiment 2 show that the pop-out is fully due to the luminance change and not to the color change. The results of Experiments 3 and 4 show that the failure to find a pop-out at equiluminance cannot be attributed to the limited temporal resolution for chromatic stimuli. The results of Experiment 5 show that particular search strategies cannot be responsible for the obtained results. The results are in agreement with physiological findings regarding the parvo and magno systems.

Attention↗
PubMed1994

Attentional misguidance in visual search.

Previous research has shown that a task-irrelevant sudden onset of an object will capture an observer's visual attention or draw it to that object (e.g., Yantis & Jonides, 1984). However, further research has demonstrated the apparent inability of an object with a task-irrelevant but unique color or luminance to capture attention (Jonides & Yantis, 1988). In the experiments reported here, we reexplore the question of whether task-irrelevant properties other than sudden onset may capture attention. Our results suggest that uniquely colored or luminous objects, as well as salient though irrelevant boundaries, do not appear to capture attention. However, these irrelevant features do appear to serve as landmarks for a top-down search strategy which becomes increasingly likely with larger display set sizes. These findings are described in terms of stimulus-driven and goal-directed aspects of attentional control.

Adolescent↗
PubMed2000

[Effect of the use of echoenhancers on interobserver variability in dobutamine stress echocardiography].

INTRODUCTION: Dobutamine stress echocardiography is an accurate technique for the noninvasive diagnosis of coronary artery disease. However, interobserver variability is an important limitation of stress echocardiography. Image quality and echocardiographer experience have been described to influence interobserver agreement. AIM: The aim of this study was to determine whether use of contrast agents during dobutamine stress echocardiography improves the agreement between an experienced and a unexperienced observer, and if learning period would be influenced by the use of contrast. METHODS: Two blind observers interpreted all the studies: one experienced echocardiographer (A) and one unexperienced observer (B) in this technique. The contrast agent Levovist/Levograf 2.5 g was administered by two bolus (at rest and at peak stress). In all cases, second harmonic imaging and stress digitalisation packs were used. The kappa test was used to determine interobserver agreement. RESULTS: Fifty-two unselected consecutive studies in 51 patients were analyzed. Twenty-two studies were performed with contrast. The agreement between the experienced and the unexperienced observer was Kappa 0.58 and 0.52, with and without the use of contrast, with no statistically significant difference being archived. CONCLUSIONS: The routine use of contrast provides better although not significant, interobserver agreement. However, this improvement is not sufficient to substitute specific training.

Cardiotonic Agents↗
PubMed2002

Perception of brightness and brightness illusions in the macaque monkey.

Recent physiological studies show that neural responses correlated with the perception of brightness are found in cortical area V1 but not earlier in the visual pathway (Kayama et al., 1979; Reid and Shapley, 1989; Squatrito et al., 1990; Komatsu et al., 1996; Rossi et al., 1996; MacEvoy et al., 1998; Rossi and Paradiso, 1999; Hung et al., 2001; Kinoshita and Komatsu, 2001; MacEvoy and Paradiso, 2001). However, these studies are based on comparisons of neural responses in animals with brightness perception in humans. Very little is known about the perception of brightness in animals typically used in physiological experiments. In this study, we quantify brightness discrimination, brightness induction, and White's effect in macaque monkeys. The results show that, qualitatively and quantitatively, the perception of brightness in macaques and humans is quite similar. This similarity may be an indication of common underlying neural computations in the two species.

Animals↗
PubMed1986

The effect of periarcuate lesions in the monkey on the performance of symmetrically and asymmetrically reinforced visual and auditory go, no-go tasks.

Monkeys with lesions restricted to the periarcuate region of the frontal cortex were impaired on go, no-go tasks in which, depending on the stimulus present on any given trial, they were rewarded either for pushing a manipulandum or for withholding this response for a given period of time. By contrast, these animals were able to learn at a normal rate go, no-go tasks in which they were rewarded if they responded in the presence of a "positive" stimulus, but not in the presence of a "negative" stimulus. In the latter situation, responding in the presence of the "negative" stimulus was extinguished through non-reward, whereas the tasks on which impairments were demonstrated required solution on the basis of a conditional rule: If stimulus A, respond, and if stimulus B, withhold responding, to receive reward. Because the 2 experimental situations were identical in every respect except for the one critical difference in the testing procedure, the present set of experiments provides a powerful demonstration of the involvement of the periarcuate cortex in conditional learning with exteroceptive stimuli.

Animals↗
PubMed1984

An early and a late developing system for learning and retention in infant monkeys.

On the evidence that memory formation and habit formation represent two qualitatively different learning processes based on separate neural mechanisms, the functional development of these two processes was followed ontogenetically. Separate groups of rhesus monkeys of different ages were tested in delayed nonmatching-to-sample and 24-hr concurrent discrimination learning, considered to be measures of recognition memory and discrimination habit formation, respectively. The youngest group of infant monkeys failed to learn the nonmatching task until they were approximately 4 months old. With further maturation, learning ability on this task gradually improved, yet it did not reach adult levels of proficiency even at 1 year of age. Postlearning evaluation with long delays and lists confirmed this slow ontogenetic development of recognition memory to adult levels of function. By contrast, infant monkeys 3-4 months old learned to discriminate long lists of object-pairs about as quickly as adult monkeys despite the use of 24-hr intertrial intervals. This striking dissociation in the ability of infants on the two tasks closely resembles the dissociation first found in adult monkeys rendered amnesic by limbic lesions. The results suggest that whereas the nonlimbic habit system matures early in infancy, the limbic-dependent memory system develops only slowly.

Age Factors↗
PubMed1998

[Memory and learning abilities in everyday life of the elderly].

Self-evaluations by adults (varying in age from 45-92 years) of their memory and learning abilities were investigated and related to performance on laboratory and ecological memory tasks. Hardly any association was found between subjective and objective measures. Self-evaluations were strongly influenced by (systematically varied) frames of reference: optimistic in comparisons with other people, pessimistic in comparisons with their own previous level of functioning. The most frequent problems were 'learning something new' and 'remembering names'. In contrast to external memory aids, cognitive strategies were rarely used spontaneously. Strategy training led to significant improvement of performance, that remained stable at follow-up. A further opportunity for improving performance was realized by ergonomic adaptations of computerized systems (teleshopping). Problems in learning to use such systems were strongly reduced by decreasing the load on working memory and by adapting the system to existing knowledge and skills of the users. A general observation in the different projects was that age-differences could explain only a small percentage of the variance in subjective and objective memory measures.

Adaptation, Psychological↗
PubMed2003

Human theta oscillations related to sensorimotor integration and spatial learning.

oscillations in the rat hippocampus have been implicated in sensorimotor integration (Bland, 1986), especially during exploratory and wayfinding behavior. We propose that human cortical activity coordinates sensory information with a motor plan to guide wayfinding behavior to known goal locations. To test this hypothesis, we analyzed invasive recordings from epileptic patients while they performed a spatially immersive, virtual taxi driver task. Consistent with this hypothesis, we found oscillations during both exploratory search and goal-seeking behavior and, in particular, during virtual movement, when sensory information and motor planning were both in flux, compared with periods of self-initiated stillness. oscillations had different topographic and spectral characteristics during searching than during goal-seeking, suggesting that different cortical networks exhibit depending on which cognitive functions are driving behavior (spatial learning during exploration vs orienting to a learned representation during goal-seeking). In contrast, oscillations in the beta band appeared to be related to simple motor planning, likely a variant of the Rolandic mu rhythm. These findings suggest that human cortical oscillations act to coordinate sensory and motor brain activity in various brain regions to facilitate exploratory learning and navigational planning.

Adolescent↗
PubMed2004

Dorsal striatum and stimulus-response learning: lesions of the dorsolateral, but not dorsomedial, striatum impair acquisition of a stimulus-response-based instrumental discrimination task, while sparing conditioned place preference learning.

While some evidence suggests that the dorsal striatum is important for stimulus-response learning, disagreement exists about the relative contribution of the dorsolateral and dorsomedial striatum to this form of learning. In the present experiment, the effects of lesions of the dorsolateral and dorsomedial striatum were investigated on two tasks that differentially require the development of stimulus-response learning. The first task utilized an operant conditional discrimination task, which is likely to rely heavily upon stimulus-response learning. The second task looked conditioned place preference learning, a task that is unlikely to require the development of stimulus-response associations. Animals with lesions of the dorsolateral striatum were impaired on the operant conditional discrimination task, but retained the ability to learn the conditioned place preference task. In contrast, animals with lesions of the dorsomedial striatum were not found to be impaired on either task used in the present experiment. These results suggest that the dorsolateral striatum is necessary for the successful acquisition of tasks that place a demand upon stimulus-response learning, while the dorsomedial striatum is not involved in this type of learning.

Amygdala↗
PubMed1989

Medial versus lateral hyperstriatal lesions in pigeons: effects on autoshaping, non-matching-to-sample and spatial discrimination learning at short and long intertrial intervals.

Three experiments contrasted the effects of medial and lateral hyperstriatal lesions in pigeons. Expt. 1 found that both types of lesion obtained slower acquisition of autoshaping, compared to unoperated controls. No group differences in maintained rate of autoshaped responding were found. Expt. 2 found that lateral but not medial lesions disrupted choice performance in a non-matching-to-sample (NMTS) task, in which initial preference was for the correct stimulus; birds with lateral lesions responded more slowly to the sample stimulus than did birds with medial lesions. Expt. 3 found that medial but not lateral lesions disrupted both acquisition and reversal of a spatial discrimination at a long, but not at a short intertrial interval (ITI). Medial lesions damage primarily the hyperstriatum accessorium and lateral lesions, the hyperstriatum ventrale; but no significant correlations between the extent of damage to either of these structures and severity of behavioural disruption were obtained. Implications of these findings for theoretical accounts of hyperstriatal involvement in learning processes are discussed.

Animals↗
PubMed2005

The role of dopamine in cognitive sequence learning: evidence from Parkinson's disease.

Electrophysiological and computational studies suggest that nigro-striatal dopamine may play an important role in learning about sequences of environmentally important stimuli, particularly when this learning is based upon step-by-step associations between stimuli, such as in second-order conditioning. If so, one would predict that disruption of the midbrain dopamine system--such as occurs in Parkinson's disease--may lead to deficits on tasks that rely upon such learning processes. This hypothesis was tested using a "chaining" task, in which each additional link in a sequence of stimuli leading to reward is trained step-by-step, until a full sequence is learned. We further examined how medication (L-dopa) affects this type of learning. As predicted, we found that Parkinson's patients tested 'off' L-dopa performed as well as controls during the first phase of this task, when required to learn a simple stimulus-response association, but were impaired at learning the full sequence of stimuli. In contrast, we found that Parkinson's patients tested 'on' L-dopa performed better than those tested 'off', and no worse than controls, on all phases of the task. These findings suggest that the loss of dopamine that occurs in Parkinson's disease can lead to specific learning impairments that are predicted by electrophysiological and computational studies, and that enhancing dopamine levels with L-dopa alleviates this deficit. This last result raises questions regarding the mechanisms by which midbrain dopamine modulates learning in Parkinson's disease, and how L-dopa affects these processes.

Aged↗
PubMed2005

A refined model of sleep and the time course of memory formation.

Research in the neurosciences continues to provide evidence that sleep plays a role in the processes of learning and memory. There is less of a consensus, however, regarding the precise stages of memory development during which sleep is considered a requirement, simply favorable, or not important. This article begins with an overview of recent studies regarding sleep and learning, predominantly in the procedural memory domain, and is measured against our current understanding of the mechanisms that govern memory formation. Based on these considerations, I offer a new neurocognitive framework of procedural learning, consisting first of acquisition, followed by two specific stages of consolidation, one involving a process of stabilization, the other involving enhancement, whereby delayed learning occurs. Psychophysiological evidence indicates that initial acquisition does not rely fundamentally on sleep. This also appears to be true for the stabilization phase of consolidation, with durable representations, resistant to interference, clearly developing in a successful manner during time awake (or just time, per se). In contrast, the consolidation stage, resulting in additional/enhanced learning in the absence of further rehearsal, does appear to rely on the process of sleep, with evidence for specific sleep-stage dependencies across the procedural domain. Evaluations at a molecular, cellular, and systems level currently offer several sleep specific candidates that could play a role in sleep-dependent learning. These include the upregulation of select plasticity-associated genes, increased protein synthesis, changes in neurotransmitter concentration, and specific electrical events in neuronal networks that modulate synaptic potentiation.

Adaptation, Physiological↗
PubMed1995

Rotorod sensorimotor learning in cerebellar mutant mice.

Lurcher mutant mice, characterized by degeneration of cerebellar granule and Purkinje cells, were compared to normal littermate controls in a rotorod test, consisting of a wheel turning at constant speed which required on the part of the animal postural adjustments in order to maintain equilibrium. Identical baseline rates for the two groups were assured by changing the speed and size of the rotating rod. Although both groups were able to learn the task, the fall latencies of normal mice exceeded those of lurchers. These results indicate that cerebellar cortical atrophy does not abolish this form of sensorimotor learning. However, brain-damaged animals are unable to reach the same level of performance as normal animals. In contrast to the results in lurcher mutants, no sensorimotor learning was displayed by hot-foot mutants and staggerer mutants.

Animals↗
PubMed1982

Learning disabilities theory and Soviet psychology: a comparison of basic assumptions.

Critics both within and outside the Learning Disabilities (LD) field have pointed to the weaknesses of LD theory. Beginning with the premise that a significant problem of LD theory has been its failure to explore fully its fundamental assumptions, this paper examines a number of these assumptions about individual and social development, cognition, and learning. These assumptions are compared with a contrasting body of premises found in Soviet psychology, particularly in the works of Vygotsky, Leontiev, and Luria. An examination of the basic assumptions of LD theory and Soviet psychology shows that a major difference lies in their respective nondialectical and dialectical interpretation of the relationship of social factors and cognition, learning, and neurological development.

Child↗
PubMed2006

Executive control and learning pattern on the CVLT.

We evaluated a 23 year-old man after recovery from encephalitis. In contrast to the expected pattern of increasingly better acquisition across the 5 learning trials of the California Verbal Learning Test (CVLT-2), he produced a "J-shaped" curve (Trials 1-5: 8,6,6,9,11). Because he also demonstrated excessive levels of proactive interference as well as poor divided attention, we hypothesized that his atypical learning pattern was due to a build-up of proactive interference secondary to executive dyscontrol. Using a large sample of 4462 healthy adult men, we identified four groups exhibiting various learning patterns. We found that a learning pattern similar to this patient (i.e., a drop after trial 1 followed by recovery) was rare (1.1% of the sample). Individuals with this learning pattern demonstrated increased perseverative responses, as well as greater difficulty maintaining cognitive set on the Wisconsin Card Sorting Test, decreased attentional control on the Paced Auditory Serial Addition Test, and greater levels of proactive interference on the CVLT. Taken together, the results of the study suggest that an early drop, followed by a recovery in learning trial performance, is associated with executive dyscontrol.

Adult↗
PubMed1995

Sibling interaction of children with learning disabilities: a comparison of autism and Down's syndrome.

Two potentially contrasting hypotheses can be generated about sibling interactions involving a child with Down's syndrome or autism. Research on siblings would predict that learning disabled children adopt responsive roles. Studies of children with autism would predict impoverished interactions. Home observations were conducted on 30 sibling pairs involving children with autism or Down's syndrome. Both hypotheses were partially supported. All learning disabled children engaged in frequent bouts of interaction, usually directed by their sibling. While children with autism engaged in fewer bouts and imitated less, they did reciprocate their siblings' initiations. Sibling encounters provide a unique opportunity for such children to learn about social relationships.

Autistic Disorder↗
PubMed2001

Implicit versus explicit memory function in children with Down and Williams syndrome.

The present study was aimed at evaluating implicit memory processes in participants with Williams syndrome and comparing them to children with Down syndrome and to mental-age matched typically developing children. For this purpose, tests of verbal and visuo-perceptual explicit memory, verbal and visual repetition priming as well as procedural learning tasks were administered to 12 participants with Williams syndrome, 14 with Down syndrome and 32 typically developing children. Participants with Williams syndrome showed a level of repetition priming similar to that of mental-age typically developing controls. In contrast, children with Williams syndrome showed a reduced learning rate in the two procedural tasks. As regards children with Down syndrome, we document comparable implicit memory abilities. In contrast, regarding explicit memory, typically developing children performed better than individuals with Down syndrome. This finding is relevant for our knowledge about the qualitative aspects of the anomalous cognitive development in individuals with intellectual disabilities and the neurobiological substrate underlying this development.

Child↗