SEARCH · Search PubMed

Results for “Visual Pathways”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,315 records · Page 73Linked to original sources

PubMed1980

Device for measuring the precision of eye-hand coordination while tracking changing size.

Psychophysical evidence supports the idea that the human visual pathway computes an object's rate of change of angular size rather independently of the object's trajectory and rather independently of other visual parameters, including contrast and intensity. This independence could provide a basis for accurately judging the component of an object's velocity along a line through the eye in the working visual environment where many visual parameters vary simultaneously. We describe a procedure for quantifying a subject's ability to track changing size, and illustrate the procedure with preliminary experimental data. The subject's R.M.S. tracking errors are displayed in three frequency bands. Our device also measures the perturbing effect of sideways motion upon the subject's ability to track changing size. Such data may go some way to predict a subject's performance in tasks of eye-limb coordination, especially where visual information is largely restricted to the changing-size channel.

Aerospace Medicine↗

PubMed1975

Subclinical optic neuropathy in multiple sclerosis. How early VER components reflect axon loss and conduction defects in optic pathways.

The pathological effect of multiple sclerosis in the visual pathways consists of axonal demyelination and axonal loss. These two consequences of the disease, even in its subclinical stages, are reflected in changes in the initial component of the visual evoked response (VER) affecting its latency, configuration, or both. These abnormal early components of the VER were recorded in 25 patients with multiple sclerosis, only 10 of whom had any indication of visual involvement that could be documented historically or by conventional ophthalmic investigation.

Evoked Potentials↗

PubMed1993

Clinical implications of the fibre order in the optic pathway of primates.

Traditional neuro-ophthalmologic accounts of the optic pathway in primates stipulate that two half-retinal maps, one from each optic nerve, are combined within the chiasmatic region to yield a single, unified representation of the contralateral visual hemi-field in each optic tract. Yet visual disturbances produced by compromise to the visual pathways in the region of the describes recent neuroanatomical studies in monkeys that contradict those classical accounts but are consistent with the incongruous field defects and the functionally selective visual impairments documented in the clinical literature.

Animals↗

PubMed1989

Electrophysiologic testing techniques for children.

This practical article for clinical electrophysiologists discusses the evaluation of infant and child patients' visual systems using electroretinographic (ERG), electrooculographic (EOG), and visually evoked potential (VEP) techniques. These techniques not only help to secure specific diagnoses, but by systematic assessment of function along the visual pathways can also localize dysfunction underlying visual deficits of pediatric patients. Among children, development as well as disease can affect electrophysiological parameters. Therefore diagnosis of normal or abnormal depends critically on an adequate description of normal responses for age. Procedures that the authors have found feasible, reliable, and valid are summarized. Standardization of pediatric testing appears to be an important next step. The power of ERG, EOG and VEP recordings to demonstrate the neurophysiological basis for pediatric visual impairment is predicted to stimulate further research in this area.

Adult↗

PubMed1985

Visual evoked potentials in ataxia telangiectasia.

Pattern reversal visual evoked potentials (VEPs) elicited in four patients with ataxia telangiectasia revealed normal results in two and absent responses in two. The pathogenesis of the VEP abnormalities is discussed. It is surmised that the VEP changes reflect progressive degeneration of the nerve fibres in the anterior visual pathway, as in Friedreich's ataxia.

Ataxia Telangiectasia↗

PubMed2006

Optic nerve axonal pathology is related to abnormal visual evoked responses in AIDS.

Electrophysiological studies in subjects with HIV/AIDS demonstrate subtle changes in the visual pathway even in the absence of visual symptoms. But the pathological correlate of the electrophysiological abnormalities is largely unknown. This study attempts to correlate pathological changes in the retina and intraorbital portion of optic nerve in four drug naïve patients of AIDS caused by HIV-1 clade C, who had abnormalities in the visual evoked potentials recorded antemortem. Three had no visual complaints and one patient had sudden loss of vision in the right eye. In all four patients, the visual evoked potentials disclosed variable prolongation of P100 latencies. Histologically axonal cytoskeletal breakdown and depletion in the optic nerves was the cardinal finding with variable myelin loss, even in the absence of overt visual dysfunction, or infective retinitis. The axonal loss was maximal in the symptomatic case. Retinal ganglion cell depletion was seen in only two patients. Sectoral infiltration of the optic nerve by cryptococci and Cryptococcal choroiditis was the only opportunistic infection to involve the eye. Axonal pathology in the optic nerve appears to be related to the abnormalities recorded in visual evoked potentials even in the absence of overt clinical symptoms. Opportunistic infections could be contributing to the axonal pathology in the optic nerve in patients with AIDS.

Acquired Immunodeficiency Syndrome↗

PubMed1996

The role of ERG/VEP and eye movement recordings in children with ocular motor apraxia.

Ocular motor apraxia (OMA) is characterised by an intermittent inability to initiate voluntary saccades, and a failure to produce optokinetic and vestibular quick phases. Some patients have no other abnormalities (idiopathic OMA), whereas in others it appears associated with a variety of neurological conditions which may affect the sensory visual pathway. Electroretinograms (ERGs), flash and pattern visual evoked potentials (VEPs) and eye movements were assessed in 53 children with OMA (age range 17 days to 14 years) to determine their efficacy in helping to distinguish between idiopathic and non-idiopathic cases. Seven patients (13.2%) had idiopathic OMA and the remaining 46 (86.8%) had other associated clinical conditions. All patients had episodes of absent quick phases ('lock up') during optokinetic nystagmus (OKN) and/or vestibular testing. Flash ERGs were abnormal in only 7 patients (13.2%); 6 had syndromes involving a pigmentary retinopathy (Joubert's, Bardet-Biedl, infantile Refsum's, Kearns-Sayre's), and the seventh had a cone dystrophy with vermis hypoplasia. VEPs were normal in all 7 patients with idiopathic OMA. Thirty-three (72%) patients with OMA in association with neurological conditions had abnormal VEPs and 13 had normal VEPs (28%). There was a significant positive correlation between VEP abnormality and poor OKN gain. VEP/ERG testing and eye movement studies are useful when OMA is suspected as they help in distinguishing isolated idiopathic cases from those with more widespread neurological abnormalities.

Adolescent↗

PubMed1998

Vision and attention. I: Current models of visual attention.

Visual attention has been defined by different researchers and clinicians in a variety of ways that are sometimes conflicting or confusing. This paper will provide a unified definition of visual attention, as well as a putative neurophysiological mechanism that is consistent with this unified definition. In addition, recent data on the mechanisms of visual attention will be presented, including its spatial organization and temporal dependencies, as well as the role of parallel visual pathways in its activation.

Attention↗

PubMed2006

Visual evoked potentials in neonatal hyperbilirubinemia.

The management of neonatal hyperbilirubinemia is very standardized. However, there is a lack of an objective method to evaluate the cerebral effects of bilirubin apart from brainstem auditory evoked potentials. There were few studies evaluating the effects of hyperbilirubinemia or phototherapy on the visual pathway in infants with hyperbilirubinemia. Serial visual evoked potentials of two groups of term neonates (N = 24)--group 1 with moderate hyperbilirubinemia (n = 16) and group 2 with severe hyperbilirubinemia (n = 8)--were evaluated prospectively. All infants had regular physical, neurologic, visual, and auditory evaluations until 3 years. Four (16%) had abnormal visual evoked potentials before 1 year, and the abnormalities returned to normal thereafter. There was no significant difference in visual evoked potentials between the two groups. All had normal neurodevelopmental status by 3 years, with the exception of one child from the severe group with ABO incompatibility with transient mild motor delay, hypotonia, and abnormal visual evoked potential. There were no abnormal effects of phototherapy on visual evoked potentials in infants with neonatal hyperbilirubinemia after 1 year of age. Although our sample size was small, the results suggest that the effects of hyperbilirubinemia on visual evoked potentials might be transient. (J Child Neurol 2006;21:58-62).

Child Development↗

PubMed2006

Perceptual issues in the use of head-mounted visual displays.

OBJECTIVE: We provide a review and analysis of much of the published literature on visual perception issues that impact the design and use of head-mounted displays (HMDs). BACKGROUND: Unlike the previous literature on HMDs, this review draws heavily from the basic vision literature in order to help provide insight for future design solutions for HMDs. METHOD: Included in this review are articles and books found cited in other works as well as articles and books obtained from an Internet search. RESULTS: Issues discussed include the effect of brightness and contrast on depth of field, dark focus, dark vergence, and perceptual constancy; the effect of accommodation-vergence synergy on perceptual constancy, eyestrain, and discomfort; the relationship of field of view to the functioning of different visual pathways and the types of visual-motor tasks mediated by them; the relationship of binocular input to visual suppression; and the importance of head movements, head tracking, and display update lag. CONCLUSION: This paper offers a set of recommendations for the design and use of HMDs. APPLICATION: Consideration of the basic vision literature will provide insight for future design solutions for HMDs.

Computer Terminals↗

PubMed1975

[Pathological visual field and brain tumor].

The general relationships between an operatively or autoptically localized tumor and the visual field determined by means of ikineticer perimetry are investigated, the patient stock being a total of 1756 neurosurgical brain-tumor inpatients. Examination of the visual field was possible with four fifths of the brain-tumor patients. Hemianopic, quadrantanopsic, or scotomatous defects of a topically localizable nature could be found in almost one third of the total patient stock available for examination. The clinically particularly interesting criteria of localization of homonymous-hemianopsia defects such as macular sparing and incongruence/congruence of visual field changes should be of no importance to the localization within the visual pathway of brain-tumor patients.

Blindness↗

PubMed1990

Visually evoked potentials and simple reaction times to visual stimuli in chronic disulphide intoxication.

The relationship between parameters of visually evoked potentials (VEPs) and the results of a psychological test assessing the speed of motor reaction to visual stimuli was examined in 21 patients with chronic carbon disulphide intoxication. Correlations obtained suggest cerebral disfunction of the visual pathway and diminished ability to transform visual information to motor reaction at the level of the cortical association centre.

Adult↗

PubMed2005

On the impact of attention and motor planning on the lateral geniculate nucleus.

Although the lateral geniculate nucleus (LGN) is one of the most thoroughly characterized thalamic nuclei, its functional role remains controversial. Traditionally, the LGN in primates has been viewed as the lowest level of a set of feedforward parallel visual pathways to cortex. These feedforward pathways are pictured as connected hierarchies of areas designed to construct the visual image gradually - adding more complex features as one marches through successive levels of the hierarchy. In terms of synapse number and circuitry, the anatomy suggests that the LGN can be viewed also as the ultimate terminus in a series of feedback pathways that originate at the highest cortical levels. Since the visual system is dynamic, a more accurate picture of image construction might be one in which information flows bidirectionally, through both the feedforward and feedback pathways constantly and simultaneously. Based upon evidence from anatomy, physiology, and imaging, we argue that the LGN is more than a simple gate for retinal information. Here, we review evidence that suggests that one function of the LGN is to enhance relevant visual signals through circuits related to both motor planning and attention. Specifically, we argue that major extraretinal inputs to the LGN may provide: (1) eye movement information to enhance and bind visual signals related to new saccade targets and (2) top-down and bottom-up information about target relevance to selectively enhance visual signals through spatial attention.

Afferent Pathways↗

PubMed1999

Sarcoidosis of the eye, orbit, and central nervous system. Role of MR imaging.

Sarcoidosis, a systemic disease of unknown cause, frequently involves the eye, orbit, and central nervous system. The MR imaging findings of orbital and optic pathway sarcoidosis may closely resemble several other orbital and intracranial diseases. This article reviews MR imaging findings of sarcoidosis when it involves the eye, orbit, and visual pathways. Careful review of MR findings and other neuroimaging findings and clinical characteristics will reduce the incidence of mistaking optic nerve and chiasmal sarcoidosis for meningioma or glioma.

Adolescent↗

PubMed2003

Contrast-processing dysfunction in both magnocellular and parvocellular pathways in migraineurs with or without aura.

PURPOSE: To assess contrast-discrimination thresholds in patients with migraine who have manifest visual field loss. This study was undertaken to determine whether contrast processing abnormalities in migraineurs are more readily identified by using stimuli that elicit a response from the subject that depends, at least in part, on adaptation mechanisms, and if so, whether deficits appear more pronounced in magnocellular (M) or parvocellular (P) visual pathways. METHODS: Ten patients with migraine who had abnormal visual fields measured with flicker perimetry but had normal standard automated perimetry (SAP) thresholds participated, along with 15 age-matched control subjects. Contrast-discrimination performance was assessed with the steady-pedestal (magnocellular) and pulsed-pedestal (parvocellular) stimuli of Pokorny and Smith for seven pedestal luminances between 15 and 60 cd/m(2) on a background of 30 cd/m(2). Subjects were tested foveally and midperipherally at 12.5 degrees. Migraineurs were tested in the quadrant of worst visual field performance. Control subjects were assessed in locations matched to those of the migraine group. RESULTS: Foveal performance was not significantly different between the migraine and control groups for either task. At 12.5 degrees the migraine group had significantly raised thresholds for both conditions. Effect size statistics revealed similar deficit magnitudes for each test (steady pedestal, -1.06; pulsed pedestal, -1.04). CONCLUSIONS: Dysfunction in both the M and P pathways was identified in the midperipheral visual field of the migraine group. The P pathway dysfunction was not identified by SAP. These findings support the possibility of nonselective neural adaptation abnormalities in some subjects with migraine.

Adult↗

PubMed1993

Two visual systems in one brain: neuropils serving the principal eyes of the spider Cupiennius salei.

Principal (anterior median) eyes of the wandering spider Cupiennius are served by three successive neuropils, the organization of which is distinct from those serving secondary eyes. Photoreceptors terminate in the first optic neuropil amongst second order neurons with overlapping dendritic fields. Second order neurons terminate at various depths in anterior median eye medulla where they are visited by bush-like dendritic trees of third order projection neurons. These supply tracts which extend into the "central body." This crescent-shaped neuropil lies midsagittally in the rear of the brain near its dorsal surface. It is organized into columns and it supplies both columnar and tangential efferents to other brain centers. The supply to and organization of the "central body" neuropil is reminiscent of retinotopic neuropils supplying the lobula of insects. Channels to the "central body" comprise one of two concurrent visual pathways, the other provided by the secondary eyes supplying the "mushroom body." We suggest that principal eye pathways may be involved in form and texture perception whereas secondary eyes detect motion, as is known for jumping spiders. Our data do not support Hanström's classical view that the "central body" is specifically associated with web-building, nor that it is homologous to its namesake in insect brains.

Afferent Pathways↗

PubMed2005

Direction selectivity of neurons in the striate cortex increases as stimulus contrast is decreased.

Various properties of external scenes are integrated during the transmission of information along central visual pathways. One basic property concerns the sensitivity to direction of a moving stimulus. This direction selectivity (DS) is a fundamental response characteristic of neurons in the visual cortex. We have conducted a neurophysiological study of cells in the visual cortex to determine how DS is affected by changes in stimulus contrast. Previous work shows that a neuron integration time is increased at low contrasts, causing temporal changes of response properties. This leads to the prediction that DS should change with stimulus contrast. However, the change could be in a counterintuitive direction, i.e., DS could increase with reduced contrast. This possibility is of intrinsic interest but it is also of potential relevance to recent behavioral work in which human subjects exhibit increased DS as contrast is reduced. Our neurophysiological results are consistent with this finding, i.e., the degree of DS of cortical neurons is inversely related to stimulus contrast. Temporal phase differences of inputs to cortical cells may account for this result.

Animals↗

PubMed1996

Visual evoked potential evidence for magnocellular system deficit in dyslexia.

Some recent studies on dyslexia have suggested a selective abnormality in the magnocellular visual pathway. To verify this hypothesis, we investigated motion-onset visual evoked potentials (VEPs) (predominantly testing the magnocellular system) as well as pattern-reversal VEPs (presumably testing the parvocellular system) in 20 dyslexics and 16 controls (both groups with a mean age of 10.0 years). Although the latencies and amplitudes of the main positive peak of pattern-reversal VEPs did not differ between the dyslexic and control group, the motion specific negative peak of motion-onset VEPs was significantly delayed (p < 0.001) in dyslexics. Our results confirm a selective magnocellular pathway disorder in dyslexics and indicate that the motion-onset VEPs might serve as an objective method for early diagnosis of dyslexia.

Child↗