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PubMed1978

Reading reversals and developmental dyslexia: a further study.

The pattern of errors in reading isolated words was studied in two groups of children with respect, particularly, to reversals of letter sequence and letter orientation. One group (the Institute group) consisted of children 8 to 10 years old who had been diagnosed "dyslexic" according to medical and psychoeducational criteria. The other (the School group) included all the children in a second-year elementary school class (see Liberman, Shankweiler, Orlando, Harris and Berti, 1971) who fell into the lowest third on a standard test of reading achievement. Although the Institute children were somewhat poorer in word recognition than the backward readers selected purely on psychometric grounds, the groups did not differ significantly in the incidence of reversal errors. Also, for both groups, reversals represented a small proportion of the total number of reading errors. The performance of the two groups differed in two respects: in relation to directional bias in letter reversals and in the presence or absence of a significant correlation between letter-reversing and word-reversing tendencies. It was concluded from this that directional problems do not loom large in importance in most cases of reading backwardness, but may provide an additional source of difficulty for some dyslexic children. Other aspects of the error pattern were remarkably the same for both groups. The bulk of reading errors made by both groups reflect their common difficulties in phonemic segmentation of words in the lexicon, in phonetic recoding, and in mastery of the orthography--difficulties, in short, with linguistic characteristics of words rather than with their properties as visual patterns.

Achievement↗
PubMed1978

The role of spatial redundancy in grapheme recognition: perception or inference?

The question under investigation is whether spatial redundancy operates by restricting the number of valid alternatives at each serial position or whether it serves a perceptual function by keeping visually confusable graphemes from appearing in the same array and/or maximizing the distance between such graphemes when they do occur in the same array. The first experiment used the same-different task to establish a confusion matrix for 12 non-linguistic symbols. The spatial relation between the members of two pairs of confusable symbols was manipulated in a second experiment, which had subjects look for the presence or absence of a predetermined target symbol in single six-symbol linear arrays. Facilitation was found to be dependent upon the perceptual consequences of serial position constraint rather than upon the constraint per se. The constraint was most effective when it served to prevent members of visually confusable pairs from occurring in the same array. Since spatial redundancy may operate at the feature extraction stage by minimizing competition for the same sets of feature detectors and since words are likely to be high in spatial redundancy, the possibility is raised that part of the word superiority effect may be due to visual factors rather than to linguistic context.

Form Perception↗
PubMed1986

Assessment of acuity of amblyopic subjects using face, grating, and recognition stimuli.

For amblyopic subjects, square-wave gratings, such as those used in preferential looking tests of infants' vision, yield more optimistic estimates of visual acuity than complex stimuli such as letters. A complex stimulus--a schematic face pattern--has recently been shown (Harris et al, IOVS 25:782, 1984) to permit preferential looking estimates of acuity of infants with normal eyes. In the present study, older amblyopic subjects had acuities measured with the face stimulus as well as gratings and standard recognition tests. Acuities measured with the face stimulus agreed better with the results of the standard recognition tests than did those obtained with gratings. Thus, if amblyopia of infants and young children affects spatial vision in a manner similar to that of older children and adults, one would anticipate that complex stimuli, such as the face pattern, would complement current assessments of young pediatric patients.

Adolescent↗
PubMed1992

[Evaluation algorithm for eye movement patterns during a problem solving task].

Cognitive processes are accompanied by eye movements, which are interrupted by fixations of an almost infinite number of points in the visual field. To investigate these processes, a systematic analysis of those movements is required to structure the long sequences of fixations. This task is possible if there are interrelationships between the ongoing thought processes and the fixations. Such interrelationships may manifest themselves through certain patterns of eye movements. It often happens that subsets of visual points are being looked at repeatedly. This is because a cognitive connection among the subset's elements is being discovered or created by such repetition. The method presented here attempts to achieve automatic recognition of fixation point patterns. Its usefulness is demonstrated using data from an experiment where eye movements were recorded while subjects were solving Raven Test items. The method may be characterized as a variant of time series analysis for nominal data. It is suitable for non-numerical data in general.

Algorithms↗
PubMed2005

A critical boundary to the left-hemisphere advantage in visual-word processing.

Two experiments explored boundary conditions for the ubiquitous left-hemisphere advantage in visual-word recognition. Subjects perceptually identified words presented directly to the left or right hemisphere. Strong left-hemisphere advantages were observed for UPPERCASE and lowercase words. However, only a weak effect was observed for AlTeRnAtInG-cAsE words, and a numerical reversal of the typical left-hemisphere advantage was observed for words in a visual prototype font (a very unfamiliar word format). Results support the theory that dissociable abstract and specific neural subsystems underlie visual-form recognition and fail to support the theory that a visual lexicon operates in the left hemisphere.

Attention↗
PubMed1984

Pattern visual evoked potentials and spatial vision in retrobulbar neuritis and multiple sclerosis.

In an attempt to resolve some of the reported disagreements between visual evoked potential (VEP) recordings and Snellen visual acuity in patients with multiple sclerosis, we compared these test results with sine-wave grating-contrast sensitivity curves. Disease that depressed visual sensitivity for high spatial frequencies, sparing low spatial frequencies, was associated with depressed visual acuity and attenuated small-check VEPs in the affected eye, while large-check VEPs were not attenuated. When visual sensitivity to all spatial frequencies was depressed, both large-check and small-check VEPs were attenuated, and Snellen acuity was reduced. In general, abnormalities in the contrast sensitivity curve predicted abnormalities in VEP amplitude, but VEP delay was less accurately predicted.

Adult↗
PubMed1992

Intra-arterial cisplatin--associated optic and otic toxicity.

Over a 22-month period, we investigated optic and otic toxicity accompanying intra-arterial cisplatin therapy. Baseline and serial neurologic and ophthalmologic examinations, visual evoked potentials, and brain-stem auditory evoked potentials were performed in six patients, aged 37 to 53 years. Patients received infraophthalmic intra-arterial cisplatin (60 mg/m2) every month for three to 10 treatments (mean, six treatments). Five of the six patients had progressive optic toxicity. In two patients, the visual evoked potential prolongation preceded acuity loss by at least 4 months. Two patients had evidence of otic toxicity by either brain-stem auditory evoked potential or click threshold and brain-stem auditory evoked potential. Intra-arterial cisplatin neurotoxicity may be significant in patients with already limited survival. Visual evoked potential and brain-stem auditory evoked potential should be used to monitor patients receiving potentially neurotoxic therapy.

Adult↗
PubMed1982

Voluntary alteration of visual evoked potentials.

Fifteen normal adults had pattern-shift visual evoked potentials (PSVEPs) using monocular checkerboard pattern reversal. Subjects were instructed to concentrate on the pattern in the first set of trials and then to avoid perceiving it in the second set. Direct, continuous visual observation ensured that the eye remained open and fixed on the pattern. Nonetheless, a third of the subjects could spontaneously alter or obliterate the PSVEP using several maneuvers, including meditation, daydreaming, and convergence. Several could produce shifts in apparent PSVEP latency. With explicit instruction, most subjects could learn to alter their PSVEP by maneuvers that are inapparent even to an observent technician.

Adult↗
PubMed1998

Do visual-evoked potentials and spatiotemporal contrast sensitivity help to distinguish idiopathic Parkinson's disease and multiple system atrophy?

A large number of patients with Parkinson's disease were reported to have abnormal visual-evoked potentials (VEPs) and spatiotemporal contrast sensitivity (STCS) suggesting dopaminergic deficiency in the visual pathway, probably the retina. Until now, VEPs and STCS have not been studied in multiple system atrophy (MSA). We investigated 12 patients with idiopathic Parkinson's disease (IPD) and 12 patients with MSA. The age medians were 64.5 years for IPD and 63.5 years for MSA. None of the patients showed any ocular disease that could interfere with the results. Checkboard VEPs and STCS measurements to horizontal sinusoidal gratings were evaluated. Statistical analysis was performed, including Student's t test and two- or three-way analysis of variance. A significant interocular difference in spatial contrast sensitivity was observed in IPD, which was not present in MSA. VEPs were not delayed in MSA, whereas latency of the major component and the second negative deflection were increased in IPD. VEPs and STCS measurements might provide useful help for distinguishing IPD from MSA.

Aged↗
PubMed2001

fMRI activation in a visual-perception task: network of areas detected using the general linear model and independent components analysis.

The Motor-Free Visual Perception Test, revised (MVPT-R), provides a measure of visual perceptual processing. It involves different cognitive elements including visual discrimination, spatial relationships, and mental rotation. We adapted the MVPT-R to an event-related functional MRI (fMRI) environment to investigate the brain regions involved in the interrelation of these cognitive elements. Two complementary analysis methods were employed to characterize the fMRI data: (a) a general linear model SPM approach based upon a model of the time course and a hemodynamic response estimate and (b) independent component analysis (ICA), which does not constrain the specific shape of the time course per se, although we did require it to be at least transiently task-related. Additionally, we implemented ICA in a novel way to create a group average that was compared with the SPM group results. Both methods yielded similar, but not identical, results and detected a network of robustly activated visual, inferior parietal, and frontal eye-field areas as well as thalamus and cerebellum. SPM appeared to be the more sensitive method and has a well-developed theoretical approach to thresholding. The ICA method segregated functional elements into separate maps and identified additional regions with extended activation in response to presented events. The results demonstrate the utility of complementary analyses for fMRI data and suggest that the cerebellum may play a significant role in visual perceptual processing. Additionally, results illustrate functional connectivity between frontal eye fields and prefrontal and parietal regions.

Attention↗
PubMed1990

The human motion onset VEP as a function of stimulation area for foveal and peripheral vision.

We studied amplitude of the wave N200 of the motion-onset VEP by varying the side length of a square stimulation field between 0.5 and 7 degrees. A significant increase in amplitude was obtained between 0.5 and 1 degree of side length in central stimulation and between 0.5 and 5 degrees in 10-degree peripheral stimulation. Variations of spatial frequency between 0.34 and 6.8c/deg did not modify the amplitude size, ie, no tuning effect could be found. The results of simultaneous and separate stimulation of foveal and parafoveal regions support the observation that the stimulation field size is a minor influence. Features of motion-sensitive cortical neurons, such as those found in monkeys, could account for this behavior.

Adult↗
PubMed1989

Influence of crystalline lens on VEP latency in elderly patients.

The study was performed to compare visual evoked potentials of old aphakic and pseudophakic patients (61 to 80 years) with age-matched controls. No differences were found between latencies of the two groups. Thus it seems that increased lens density of old subjects does not influence the processing of the visual stimulus.

Aged↗
PubMed1992

Electrophysiologic evaluation of the visual pathway in children. Case reports.

Clinical findings and results of electrophysiologic evaluation of the visual pathway were studied in seven children ranging in age from 10 months to 13 years. Using skin electrodes for electroretinographic and visual evoked potential testing, we obtained reliable results without sedation or pupil dilation. The half-field stimulation was indispensable for localizing lesions along the visual pathway and thus for specific diagnosis.

Adolescent↗
PubMed1987

Contrast sensitivity and pattern visual evoked potential in patients with glaucoma.

Contrast sensitivity and pattern visual evoked potential (VEP) were measured in cases of ocular hypertension and primary open-angle glaucoma at various stages. The visual field of each eye was examined quantitatively and the retinal nerve fiber layer and optic disc were precisely assessed with magnified stereoscope fundus photography. This study revealed that contrast sensitivity of the eyes with glaucoma was within the normal range in the very early stage of the disease. As optic nerve damage advanced, high- or low-frequency loss developed. Further optic nerve damage produced a level type of loss. Pattern VEPs also showed increasing abnormalities as glaucomatous optic nerve damage progressed. Measurements of contrast sensitivity and pattern VEP were found not to be as sensitive as quantified precise visual field measurement or color stereoscopic fundus photography for detection of minor optic nerve damage in cases of early glaucoma. These methods may be useful, however, as an objective and subjective monitor of progression of optic nerve damage in glaucoma.

Adolescent↗
PubMed1977

Spatial properties of binocular neurones in the human visual system.

The spatial properties of human binocular mechanisms were investigated using the technique of subthreshold summation. Isolation of binocular mechanisms was achieved by means of interocular stimulus presentation. The contrast detection threshold for a sinusoidal test grating viewed by one eye was found to be reduced by a subthreshold grating of the same spatial frequency and orientation seen by the other eye. The interaction between the gratings was approximately linear. Threshold increased as the spatial frequencies or orientations of test and subthreshold gratings were made increasingly different. Spatial stimulus specificities measured in this way were as great for interocular presentation as for simultaneous monocular presentation. The results suggest that human contrast sensitivity for gratings may depend upon binocularly-activated neurones similar to those found in cat and monkey visual cortex.

Humans↗
PubMed1982

Responses to coloured patterns in the macaque lateral geniculate nucleus: pattern processing in single neurones.

Cell responses to complex visual patterns such as compositions of broad-band (non-monochromatic) colour areas are presented. Patterns were scanned over the receptive field, and cell response at each point was recorded. "Response patterns" were constructed which display the cell transform of the stimulus pattern. Parvocellular layer (PCL) cells in the lateral geniculate nucleus, in a very sustained fashion, signal the spectral composition of areas in the pattern, cells of different classes showing different spectral responsiveness. Little or no edge enhancement was present. Magnocellular layer (MCL) cells mark luminance steps in a pattern; they are not colour-specific. Responses to monochromatic stimuli provided a reliable guide to cell responsiveness with mixed colours. However, integration by spectrally opponent mechanisms is present with broad-band colour stimulation and partly accounts for a high variability of response patterns within the same cell class. With some cells, stimulus patterns were either shown through narrow-band colour filters, or a monochromatic background was added. Response patterns to isolated wavelength components compared with those to full colour patterns revealed an almost linear additivity of individual spectral components. Adaptation to a chromatic background, on the other hand, strongly modified the effectiveness of excitatory and suppressive components in the stimulus pattern and markedly changed the structure of a response pattern compared with the non-adapted situation.

Animals↗
PubMed1992

Long-term test-retest reliability of event-related potentials in normals and alcoholics.

The long-term test-retest reliability of event-related potentials (ERP) measures was examined in a group of 44 controls and 71 chronic alcoholics, retested after an average of 14 months. Correlational analyses revealed moderately significant test-retest correlations for visual and auditory target N1, N2, and P3 amplitudes, with significant correlations for N1, N2 and P3 latencies. Controls and alcoholics produced similar test-retest correlations for visual and auditory ERP measures. Men and women produced equally stable ERP measures over time. Overall N1 and P3 amplitudes were most reliable in both groups followed by N2 amplitude, N1 and N2 latency, and P3 latency. The stability of ERP measures found in this study over a 14-month period in both normals and chronic alcoholics supports the use of ERPs in the study of normal and disordered cognitive functioning.

Adult↗