Improvement in Vernier acuity in adults with amblyopia. Practice makes better

PURPOSE: To determine the nature and limits of visual improvement through repetitive practice in human adults with naturally occurring amblyopia. METHODS: A key measure the authors used was a psychophysical estimate of Vernier acuity; persons with amblyopia have marked deficits in Vernier acuity that are highly correlated with their loss of Snellen acuity. The experiment consisted of three phases: pretraining measurements of Vernier acuity and a second task (either line-detection thresholds or Snellen acuity) in each eye with the lines at two orientations; a training phase in which observers repetitively trained on the Vernier task at a specific line orientation until each had completed 4000 to 5000 trials; and posttraining measurements (identical to those in the first phase). Two groups of amblyopic observers were tested: novice observers (n = 6), who had no experience in making psychophysical judgments with their amblyopic eyes, and experienced observers (n = 5), who had previous experience in making Vernier judgments with their amblyopic eyes (with the lines at a different orientation) using the signal-detection methodology. RESULTS: The authors found that strong and significant improvement in Vernier acuity occurs in the trained orientation in all observers. Learning was generally strongest at the trained orientation but may partially have been transferred to other orientations (n = 4). Significant learning was transferred partially to the other eye (at the trained orientation) in two observers with anisometropic amblyopia. Improvement in Vernier acuity did not transfer to an untrained detection task. In two observers, the improvement in Vernier acuity was accompanied by a commensurate improvement in Snellen acuity. CONCLUSIONS: Some adults with amblyopia retain a significant degree of neural plasticity. Although several observers (primarily novices) showed evidence of generalized learning, several amblyopic patients showed evidence for improvement that was orientation and task specific. In this latter group of observers, the improvement appeared to reflect alterations that were, at least in part, in early neural processes that were orientation specific and were localized beyond the site of convergence of the two eyes.     

Neural plasticity and exaptation.

Comments that S. J. Gould (see record 1992-11754-001) posed something of a problem for D. M. Buss et al (see record 1998-01669-001) in his argument that human psychology links not to past evolutionary adaptations but to the coopting of previously evolved functions to do new things, or exaptation. The present author states that Buss et al observed that Gould failed to document this exaptation for any of the examples he mentioned because he could not demonstrate any "special design for the hypothesized function." He suggests that neural plasticity strongly links the brain, exaptation and human psychology. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neural plasticity and emotional memory

Posttraumatic stress disorder is the pathological replay of emotional memory formed in response to painful, life-threatening, or horrifying events. In contrast, depression is often precipitated by more social context-related stressors. New data suggest that different types of life experiences can differentially impact biochemistry, physiology, anatomy, and behavior at the level of changes in gene expression. Repeated separation of neonatal rat pups from their mother results in many long-lasting alterations in biology and behavior paralleling that in depression, including hypercortisolism. The role of the amygdala in modulating emotional memory is highlighted, as well as some of its unique properties such as metaplasticity (i.e., the differential direction of long-term adaptation, either potentiation or depression) in response to the same input as a function of the prior history of stimulation. The implications of these emerging data on the physiological and molecular mechanisms underlying emotional memory emphasize the particular importance of prevention and early intervention.     

Neural plasticity and recovery of function: An introduction.

Given that functional recovery has been a dominant theme in neuroscience for nearly 200 years, it might be thought that novel approaches now will be rare. This, in turn, might suggest that a special issue of the Canadian Journal of Psychology dedicated to functional recovery would provide few surprises. The original papers in this special issue bring a number of refreshing theoretical and methodological insights that have not only enlightened the editor, but should delight the reader as well. Three of the papers deal with functional recovery in humans. Four of the papers deal with experimental procedures that are being developed to enhance recovery of function. Two papers describe neural changes that appear to be self-protective measures used by the brain to compensate injury. Two papers deal with anatomical questions associated with loss and sparing of function. A dominant idea associated with memory impairments following brain damage or geriatric disease, such as Alzheimer's disease, is that cholinergic neurons are involved. These papers do not provide an exhaustive survey of contemporary research, but each paper does provide substantive insight into an important facet of plasticity and recovery. Although these papers indicate that we are not quite at the point that recovery can be said to be a problem of engineering, they agree that enormous practical advances are now within sight. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neural and cognitive plasticity: From maps to minds.

Some species and individuals are able to learn cognitive skills more flexibly than others. Learning experiences and cortical function are known to contribute to such differences, but the specific factors that determine an organism's intellectual capacities remain unclear. Here, an integrative framework is presented suggesting that variability in cognitive plasticity reflects neural constraints on the precision and extent of an organism's stimulus representations. Specifically, it is hypothesized that cognitive plasticity depends on the number and diversity of cortical modules that an organism has available as well as the brain's capacity to flexibly reconfigure and customize networks of these modules. The author relates this framework to past proposals on the neural mechanisms of intelligence, including (a) the relationship between brain size and intellectual capacity; (b) the role of prefrontal cortex in cognitive control and the maintenance of stimulus representations; and (c) the impact of neural plasticity and efficiency on the acquisition and performance of cognitive skills. The proposed framework provides a unified account of variability in cognitive plasticity as a function of species, age, and individual, and it makes specific predictions about how manipulations of cortical structure and function will impact intellectual capacity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neural basis for recognition confidence in younger and older adults.

Although several studies have examined the neural basis for age-related changes in objective memory performance, less is known about how the process of memory monitoring changes with aging. The authors used functional magnetic resonance imaging to examine retrospective confidence in memory performance in aging. During low confidence, both younger and older adults showed behavioral evidence that they were guessing during recognition and that they were aware they were guessing when making confidence judgments. Similarly, both younger and older adults showed increased neural activity during low- compared to high-confidence responses in the lateral prefrontal cortex, anterior cingulate cortex, and left intraparietal sulcus. In contrast, older adults showed more high-confidence errors than younger adults. Younger adults showed greater activity for high compared to low confidence in medial temporal lobe structures, but older adults did not show this pattern. Taken together, these findings may suggest that impairments in the confidence–accuracy relationship for memory in older adults, which are often driven by high-confidence errors, may be primarily related to altered neural signals associated with greater activity for high-confidence responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Language processing in aphasia: changes in lateralization patterns during recovery reflect cerebral plasticity in adults

During single word processing the negative cortical DC-potential reveals a left frontal preponderance in normal right-handers as well as in patients with a history of transient aphasia. Lateralization of DC-negativity therefore provides a reliable and robust method for the assessment of language dominance. In 11 stroke patients with permanent aphasia this physiological pattern changed to bilateral activation reflecting an additional right-hemispheric involvement in compensatory mechanisms in aphasia. Along with complete clinical recovery the classical aphasic syndromes revealed specific differences in changes of their lateralization patterns. In Broca's aphasia the initial right-hemispheric preponderance changed to a left frontal lateralization while in Wernicke's aphasia a presumably permanent shift towards the right hemisphere occurred. Differences in lateralization patterns might reflect different mechanisms of recovery such as the initial disinhibition of homologous areas contralaterally and subsequent collateral sprouting and synaptic modulation. The assessment of changes in lateralization of the cortical DC-potential during language tasks in a non-invasive, safe method with excellent time resolution that might provide further insights in the neural basis of recovery from aphasia.     

Metacontrast masking in amblyopia.

Measured the time course of visual signals arising from each eye of 4 strabismic and/or anisometropic amblyopes and 2 visually normal Ss using monoptic metacontrast masking. The amblyope Ss had 1 nonamblyopic eye, clear ocular media, and normal fundi. The method involved the brightness estimation of a high-contrast disk target whose visibility varied as a function of the stimulus onset asynchrony (SOA) of a subsequent annular mask. Results indicate that the SOA of optimal masking was delayed in the amblyopic eye compared to that of the fellow nonamblyopic eye or with normal eyes. The smaller the target, the greater was this SOA difference and the broader was the amblyopic U-shaped masking function. This finding is discussed in terms of the current model of metacontrast and represents the differential effect of the amblyopic process on human sustained and transient neurons. (French abstract) (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Photoreceptor function in unilateral amblyopia

We investigated whether photoreceptor function in amblyopic eyes differed from that in non-amblyopic eyes. Photoreceptor function was assessed with the optical Stiles-Crawford effect (SCE), psychophysical SCE, and foveal visual pigment density in both eyes of ten unilateral amblyopic subjects. Optical SCE and density measurements were carried out with a custom-built scanning laser ophthalmoscope (SLO). Amblyopic and normal eyes did not differ in Stiles-Crawford effect, nor in foveal visual pigment density. Contrary to suggestions in the literature, we found no indication of retinal dysfunction at the level of the cone photoreceptors in amblyopic eyes.     

Posterior polymorphous dystrophy associated with astigmatism and amblyopia in children

BACKGROUND: Posterior polymorphous dystrophy has been described in the scientific literature as having more than a casual association with keratoconus in adults. We studied four consecutive children with posterior polymorphous dystrophy who had coexisting astigmatism. In our patients, the posterior changes appeared to be associated with the corneal astigmatism, as evidenced by videokeratography. METHODS: Four consecutive cases of posterior polymorphous dystrophy in children were found over a 3-year period by one of the authors (PD). They presented with varying degrees of amblyopia in the eyes with the greater amount of posterior polymorphous dystrophy. Cycloplegic refractions and keratometry readings were performed. The more affected eyes had greater degrees of astigmatism, presumably causing the amblyopia. Whenever possible, the results were supplemented by confirmation by a corneal specialist, specular microscopy, slit-lamp photographs and videokeratography. RESULTS: Greater asymmetry of posterior polymorphous dystrophy was associated with greater astigmatism in the more affected eye. When more astigmatic anisometropia was present there was a greater amblyopia. Videokeratography of one of the patients showed that an area of confluent blebs forming a crescent shape compared exactly with a steep cylinder along the same axis. With-the-rule astigmatism was associated with a more diffuse pattern of blebs. CONCLUSION: Decreases in visual acuity in children with posterior polymorphous dystrophy may sometimes be due to an amblyopia caused by the astigmatism of asymmetric disease.     

Eradicating amblyopia before surgery

Nitric oxide (NO) is improbable as a conventional neurotransmitter. It is not an amine, amino acid, or peptide; it is not stored in synaptic vesicles or released by exocytosis; and it does not interact with specific receptor subtypes in neuronal membranes. However, NO is synthesized upon demand in the brain, diffuses to receptor sites within the enzyme guanylyl cyclase, and has neurotransmitter-like functions.     

Neural plasticity, neuropeptides and anxiety in animals--implications for understanding and treating affective disorder following traumatic stress in humans

Phenolic composition, toxicity and biodegradability of three different phenolic leachates/samples was studied. Samples A and C were the leachates from the oil-shale industry spent shale dumps at Kohtla-J?rve, Estonia. Sample B was a laboratory-prepared synthetic mixture of 7 phenolic compounds mimmicking the phenolic composition of the leachate A. Toxicity of these 3 samples was analyzed using two photobacterial test (BioTox and Microtox), Daphnia test (DAPHTOXKIT F pulex) and rotifiers' test (ROTOXKIT F). All the LC50 values were in the range of 1-10%, leachate A being the most toxic. The growth and detoxifying potential (toxicity of the growth medium was measured using photobacterial tests) of 3 different phenol-utilizing bacteria and acclimated activated sludges was studied in shake-flask cultures. 30% leachate A (altogether 0.6 mM total phenolic compounds) was too toxic to rhodococci and they did not grow. Cell number of Kurthia sp. and Pseudomonas sp. in 30% leachate A increased by 2 orders of magnitude but despite of the growth of bacteria the toxicity of the leachate did not decrease even by 7 weeks of cultivation. However, if the activated sludge was used instead of pure bacterial cultures the toxicity of the 30% leachate A was eliminated already after 3 days of incubation. 30% samples B and C were detoxified by activated sludge even more rapidly, within 2 days. As the biodegradable part of samples A and B should be identical, the detoxification of leachate A compared to that of sample B was most probably inhibited by inorganic (e.g. sulphuric) compounds present in the leachate A. Also, the presence of toxic recalcitrant organic compounds in the leachate A (missed by chemical analysis) that were not readily biodegradable even by activated sludge consortium should not be excluded.     

Occlusion therapy of Japanese children with anisometropic amblyopia without strabismus

We examined 38 children (20 boys and 18 girls) with anisometropic amblyopia without strabismus who had been treated with occlusion therapy. At the initial visit, their ages ranged from five to ten years. Their visual acuity scores improved after therapy, and this was unrelated to patient age. The amount of anisometropia, visual acuity at the initial visit, and compliance were related to improved visual acuity in the amblyopic eye. The visual acuity improved for six months after therapy. No further gains were detected thereafter.     

Intraindividual variability in cognitive performance in older adults: Comparison of adults with mild dementia, adults with arthritis, and healthy adults.

Intraindividual variability in latency and accuracy of cognitive performance across both trials and occasions was examined in 3 groups of older adults: healthy adults, adults with arthritis, and adults diagnosed with mild dementia. Participants completed 2 reaction-time and 2 episodic-memory tasks on 4 occasions. Results indicated that intraindividual variability in latency was greater in individuals diagnosed with mild dementia than in adults who were neurologically intact, regardless of their health status. Individual differences in variability were stable over time and across cognitive domains. Intraindividual variability was also related to level of performance and was uniquely predictive of neurological status, independent of level of performance. Results suggest that intraindividual variability may be a behavioral indicator of compromised neurological mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual evoked potentials in patients with refraction amblyopia in the presence of high myopia

The informative value of a method for assessing the degree of amblyopia, developed by the author, was assessed in examinations of 16 children (29 eyes) with ametropic amblyopia caused by high myopia and 41 healthy controls. The method consists in recording the pattern-reversal visual evoked potentials (VEP) evoked by 4 patterns of different checksize and contrast. A relationship has been revealed between the VEP types detected by the proposed method and the degree of amblyopia (degree of vision acuity loss). The author came to a conclusion that in ametropic amblyopia, similarly as in stimulus deprivation amblyopia, changes of VEP develop that reflect the deterioration of contrast sensitivity function in low spatial frequencies. The developed VEP method with the modifications described in this paper may be useful in the diagnosis and objective evaluation of the degree of amblyopia.     

Naso-temporal asymmetry of spatial interactions in strabismic amblyopia

PURPOSE: Naso-temporal asymmetries of visual acuity and contrast sensitivity have been reported in strabismic amblyopia and attributed to asymmetries of interocular suppression. In this study, we investigated the naso-temporal asymmetry of cortical spatial interactions in two strabismic amblyopes (one esotrope and one exotrope). METHODS: Length and width Westheimer functions were measured on both amblyopes at the 10 deg retinal eccentricity of both nasal and temporal visual fields. RESULTS: Spatial interactions in the two amblyopic eyes were more degraded in the temporal visual fields than in the nasal visual fields. A comparison with results from the preferred eyes suggested that this asymmetry was caused mainly by a loss of spatial interactions in the temporal visual fields of amblyopic eyes, with those in the nasal visual fields being normal. CONCLUSION: Our results suggest that intracortical connections underlying cortical spatial interactions might have been degraded by amblyopia. This degradation exists not only in the areas of the strabismic visual cortex responding to foveal stimuli but also in those responding to stimuli presented in the temporal visual fields.     

Active vision therapy for pseudophakic amblyopia

PURPOSE: To study the benefit of active vision therapy using various pleoptic methods in pseudophakic amblyopic children and young adults. SETTING: Daljit Singh Eye Hospital, Amritsar, India. METHODS: This study comprised 160 consecutive pseudophakic amblyopic patients who had had iris-claw lens implantation for congenital or traumatic cataract. Their ages ranged from 3.5 to 25.0 years. Before active vision treatment, visual acuity was worse than 20/200 in 63 patients (39.3%), 20/200 in 77 (48.1%), 20/120 to 20/80 in 14 (8.7%), and 20/60 in 6 (3.7%). The methods included Haidinger brushes on the synoptophore, after images, CAM stimulator, drawings on the cheiroscope, Pigeon-Cantonnet stereoscope, video games with the amblyopic eye, and exercises for promoting eye-hand coordination. Mean duration of therapy was 6 months. RESULTS: After therapy, visual acuity was worse than 20/200 in 31 patients (19.4%), 20/200 in 38 (23.7%), 20/120 to 20/80 in 41 (25.6%), 20/60 to 20/40 in 36 (22.5%), and 20/20 in 14 (8.7%). In 20 patients (12.5%), all younger than 15 years, visual acuity decreased within 1 month after treatment stopped. However, vision was rapidly restored after another session of active vision therapy. CONCLUSIONS: Active vision therapy helped improve visual acuity in the majority of young pseudophakic amblyopes.     

The role of plasticity in bimaterial fracture with ductile interlayers

Evaluation of the plasticity effects in fracture along ductile/brittle interfaces requires appropriate models for plastic dissipation in a ductile component. For thin ductile films, constitutive properties appropriate to the small volumes involved are essential for adequate modeling. Here, yield stress is of primary importance. With nanoindentation, one can obtain both a large strain flow stress as well as the far field yield stress representing the small strain elastic-plastic boundary. Using these to estimate an appropriate plastic strain energy density, the crack tip plastic energy dissipation rates associated with the interfacial crack extension can be estimated for a ductile film. With the preceding analysis, plasticity effects on the interfacial toughness have been evaluated for external measures of strain energy release rates as obtained from indentation tests using the axisymmetric bilayer theory. Comparison involved RF sputtered 200- to 2000-nm-thick Cu interlayers between oxidized silicon and sputtered tungsten. Experimental values for the Cu/SiO₂ interface increased with Cu film thickness from 1 to 15 J/m². This was in qualitative agreement with the theoretical predictions for plastic energy dissipation rates. In contrast, first-order estimates suggest that the observed interfacial toughness increases cannot be attributed to either mode mixity effects or increased intrinsic interfacial fracture energies. As such, crack tip plasticity is identified as the dominant mechanism for increasing interfacial toughness. This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October 11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite Materials Committee.