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PubMed1988

Cerebral metabolism and patterned visual stimulation: a positron emission tomographic study of the human visual cortex.

We studied the impact of visual stimulation upon cerebral metabolism in normal young men using FDG-PET. Results obtained from subjects receiving patterned visual stimulation while performing an ocular fixation task were compared with results from ocular fixation alone. Visual stimulation in the macular region of either hemifield produced significant increases in metabolism of the contralateral posterior striate cortex. Visual stimulation induced highly significant asymmetries in metabolism of the prefrontal and inferior parietal cortices. Metabolic activation in extrastriate areas tended to be right-sided. These findings support the classic notion of retinotopic organization within the primary visual sensory cortex. They also indicate that the patterns of cerebral metabolism are not equivalent between the two cerebral hemispheres. This latter finding suggests that in humans the right cerebral hemisphere may be specialized for visual processing.

Adolescent↗

PubMed1990

Spontaneous visual phenomena with visual loss: 104 patients with lesions of retinal and neural afferent pathways.

Fifty-seven percent of 104 consecutive patients with retinal or neural visual loss reported spontaneous visual phenomena (SVP). Elementary SVP occurred more commonly (51% of patients) than complex SVP (21%). SVP occur with lesions of any portion of the visual pathways. Unlike irritative hallucinations, they do not aid in localization of the lesion. SVP occur significantly more frequently with visual acuity of 20/50 or less in both eyes. These purely visual hallucinations are unlikely to herald psychiatric disease and may be release phenomena stemming from loss of inhibitory visual input.

Adolescent↗

PubMed1996

Positive spontaneous visual phenomena limited to the hemianopic field in lesions of central visual pathways.

We prospectively studied 32 patients with ischemic infarction of the retrochiasmal visual pathways. Positive spontaneous visual phenomena (PSVP) in the blind hemifield were present in 13 patients (41%). The PSVP were subdivided into phosphenes, photopsias, visual hallucinations, palinopsia, and agitated delirium with hemianopia. PSVP were never associated with auditory or other sensory positive phenomena, except in patients with agitated delirium. Patients with photopsias, phosphenes, palinopsia, and visual hallucinations had similar lesions in MRI/CT, suggesting no anatomic area unique for these four phenomena. However, there was a significant difference in the severity of associated neurologic deficits between hemianopic patients with and without PSVP. Larger lesions destroying anteriorly located visual association areas precluded the development of PSVP, which may be related to release from inhibitory input of visual regions bordering the damaged area. Patients with the syndrome of agitated delirium and hemianopia had specific lesions involving the mesial aspect of the occipital lobe, the parahippocampal gyrus, and hippocampus.

Adult↗

PubMed2003

Tentorial dural arteriovenous fistula presenting with various visual symptoms related to anterior and posterior visual pathway dysfunction: case report.

OBJECTIVE AND IMPORTANCE: Dural arteriovenous fistulae (DAVFs) not directly shunting into the cavernous sinus are an infrequent cause of visual dysfunction. An unusual case of a tentorial DAVF associated with visual symptoms related to dysfunction of the anterior and posterior visual pathway is presented. CLINICAL PRESENTATION: A 38-year-old woman with a history of long-standing bilateral proptosis experienced a sudden onset of headache and visual disturbances. Ocular examination revealed bilateral episcleral and retinal venous congestion, optic disc paleness, right superior homonymous quadrantanopsia in both eyes, and concentric narrowing of the visual field of the right eye. Angiography revealed a DAVF supplied by a falx branch arising from the left vertebral artery and both middle meningeal arteries, which drained directly into the markedly dilated vein of Galen via the basal vein of Rosenthal and the cavernous sinus into both superior ophthalmic veins. INTERVENTION: Endovascular treatment was performed in two consecutive sessions by transarterial embolization with n-butylcyanoacrylate, which resulted in occlusion of the fistula and complete clinical cure, confirmed at the 6-month follow-up examination. CONCLUSION: Various neuro-ophthalmological findings may be caused by an arteriovenous lesion remote from the optic organ as a result of rerouting of venous drainage compromising the visual pathway at different locations. Transarterial embolization of a DAVF may result in complete cure if advantageous arterial anatomy allows for flow control and occlusion of the fistulous connection with liquid adhesives.

Adult↗

PubMedDate not supplied

[Functional outcome of visually handicapped children cared for at the Department of Visual Stimulation--"Fundação Altino Ventura"].

PURPOSE: To analyze the functional outcome of visually handicapped children. METHODS: Twenty-seven children were evaluated using the standard functional PEDI test. Seventeen who attended school at "Escola Municipal Alto do Maracanã", Recife - Pernambuco, Brazil, had normal visual acuity and the other ten had visual handicap, and were cared for at Stimulation Visual Department - "Fundação Altino Ventura", in the same city. RESULTS: The children who had visual handicap showed significantly worse performance in self-care and mobility than normal children. CONCLUSION: Visual handicap may have limited the performance regarding self-care, mobility, understanding, communication, home works, in the studied group.

Activities of Daily Living↗

PubMed2001

Visual marking and the perception of salience in visual search.

In the present study, the gap paradigm originally developed by Watson and Humphreys (1997) was used to investigate whether the process of visual marking can influence the perceptual salience of a target in visual search. Consistent with previous studies (Watson & Humphreys, 1997), the results showed that search was not affected by the presence of the preceding distractors when the target was relatively low in salience. This finding suggests that visual marking can increase the efficiency of visual search by decreasing the size of the search set. However, more important, the results also showed that search was affected by the presence of the preceding distractors when the target was relatively high in salience. This finding suggests that visual marking may be limited in its ability to increase the perceptual salience of the target. Together, the results of the present study suggest that the effectiveness of visual marking may vary as a function of search context.

Fixation, Ocular↗

PubMed2000

Monocular versus binocular visual acuity as measures of vision impairment and predictors of visual disability.

PURPOSE: To examine the relationship between monocular and binocular visual acuities as predictors of visual disability in a population-based sample of individuals 65 years of age and older. METHODS: Two thousand five hundred twenty community-dwelling residents of Salisbury, Maryland, between the ages of 65 and 84 years of age were recruited for the study. Corrected visual acuity was measured monocularly and binocularly using ETDRS charts. Reading speed, face discrimination, and self-reported difficulty with visual tasks were also determined. RESULTS: Binocular acuity is predicted with reasonable accuracy by acuity in the better eye alone, but not by the widely used American Medical Association (AMA) weighted-average algorithm. The AMA algorithm significantly underestimates binocular acuity when the interocular acuity difference exceeds one line. Monocular acuity and binocular acuity were significantly better predictors of reading speed than the AMA weighted score or a recently proposed Functional Vision Score (FVS). Monocular acuity in the better eye, binocular acuity, and the AMA and FVS algorithms were equally good predictors of self-reported vision disability. None of the acuity measures were good predictors of face recognition ability. CONCLUSIONS: The binocular acuities of older individuals can be inferred from measures of monocular acuity. There is little evidence for binocular inhibition when the monocular acuities in the two eyes are unequal, as opposed to the widely used AMA algorithm for computing binocular visual impairment. For tasks that are strongly associated with visual acuity, such as reading, this association can be captured from measures of monocular acuity and does not require separate assessment of binocular acuity.

Aged↗

PubMedDate not supplied

Age-related changes in the relationship between visual evoked potentials and visually evoked cerebral blood flow velocity response.

We evaluated neurovascular coupling during normal aging using visual evoked potentials (VEPs) and visually evoked cerebral blood flow velocity responses (VEFRs). The recordings were made from a group of healthy younger and older subjects. The stimulus was a black and white checkerboard with visual contrasts of 1%, 10% and 100%. The VEFRs were measured in the posterior cerebral artery using transcranial Doppler simultaneously with VEPs from occipital leads. A significant increase in the VEFRs and VEPs in response to graded visual contrasts (p<0.01) was found in both groups. Linear regression analysis showed a significant positive association between the VEPs and the VEFRs in the younger (r=0.66, p<0.01) and older subjects (r=0.74, p<0.01). We also found significant differences in neurovascular coupling index (VEFR/VEP) between both groups at each visual contrast (p<0.01). We conclude that simultaneous recording of VEFRs and VEPs at graded visual contrasts indicated attenuated neurovascular coupling in older subjects.

Adult↗

PubMed1991

[Central visual fields in pure alexia "without hemianopsia"--visual dysfunction in the right hemifield, and alexia for "kana" words in the left].

Following a left occipito-temporal subcortical hematoma, a 57-year-old, right-handed man developed pure alexia that was more prominent in kana words, especially in kana nonwords, than in kanji letters. Although a kinetic perimetry with a Goldmann perimeter showed his visual fields to be full, a static perimetry with a Humphrey visual field analyzer disclosed decreased visual sensitivity in the right visual field in its central 30 degrees. In addition, a tachnistoscopic examination with Landolt rings revealed his visual acuity (the ability of two points discrimination) to have decreased in the right half of his central visual filed in its 3 degrees. In the right central vision, he was unable to recognize the letters, pictures or colors presented by the tachistoscope. Concerning the reading, the more letters in kana words or the higher the number of strokes in kanji letters, the more difficulty he experienced in orally reading both kana and kanji. On the contrary, in the left central vision, kanji reading was not so affected by an increased number of strokes as the kana-word reading which became difficult when the number of the letters increased. CT scan showed subcortical hematoma in the left occipitotemporal region. Magnetic resonance imaging 3 months after onset revealed a localized injury in the region between the left postero-inferior temporal lobe and the infero-lateral occipital lobe, including the fusiform gyrus. None of the splenium, the lingual gyrus or the optic area were affected. The spared structures also included the angular gyrus, the Wernicke area and their subcortical white matter.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral Hemorrhage↗

PubMed1988

Development of GABAA receptors in the central visual structures of rat brain. Effect of visual pattern deprivation.

The postnatal development of high-affinity 3H-muscimol binding to GABAA receptors was studied in the lateral geniculate nucleus, superior colliculus, frontal and visual cortex of the rat brain. In the lateral geniculate nucleus 3H-muscimol binding rises from day 10 through day 37 reaching the highest value during the entire development followed by a slight decrease until adulthood. In the superior colliculus 3H-muscimol binding increased continuously from day 10 through day 37, and then decreased until day 50 reaching the adult value. In the visual and frontal cortex, binding reached the highest levels on days 14 and 25, respectively, persisted until day 37 followed by a slight decrease until adulthood. The ontogeny of 3H-muscimol binding sites in the visual regions does not essentially differ from that in other brain regions, suggesting that the appearance of 3H-muscimol binding sites in the visual system is not correlated with the functional maturation of the visual system. Unilateral eyelid closure from day 11 until day 25 did not affect the development of GABAA receptors in any of the central visual regions examined, indicating the lack of environmentally controlled mechanism.

Animals↗

PubMed1989

Visual-visual associative learning and reward-association learning in monkeys: the role of the amygdala.

Three Cynomolgus monkeys (Macaca fascicularis) took part in an experiment on visual learning set in an automatic apparatus. Each new visual discrimination problem was solved using a visual secondary reinforcer consisting of a white line. If the monkey chose the correct stimulus (by touching it), the white line appeared over the correct stimulus. Primary food reward was delivered only after a new problem was solved to a criterion, and the problem was then replaced by a new one. Thus, within-problem learning did not rely on primary reinforcement but on the visual secondary reinforcer. The animals were trained preoperatively in visual learning set with this procedure and were assessed postoperatively for their ability to learn new visual discriminations with the same procedure. Bilateral amygdalectomy did not significantly impair the animals' learning ability in this task. Learning remained unimpaired when transection of the uncinate fascicle and of the fornix was added to amygdalectomy. The effect of bilateral amygdalectomy in this task was much less severe than in a similar task we previously studied, with auditory secondary reinforcers. The results show that the involvement of the amygdala in processes of secondary reinforcement depends on the sensory properties of the secondary reinforcer. From these and other recent results, we conclude that the sensory attributes of a reinforcer are easily associated with a discriminative stimulus when they are in the same modality and same spatial location as the discriminative stimulus and that this sensory-sensory association is independent of the amygdala.

Amygdala↗

PubMed1988

Carbon disulfide effects on the visual system. I. Visual thresholds and ophthalmoscopy.

The visual effects of carbon disulfide exposure were studied in macaque monkeys with measurements of visual thresholds, fluorescein angiography and fundus photography. Five monkeys were exposed by inhalation for 6 hr a day, 5 days a week to 256 ppm carbon disulfide (CS2). The motor dysfunction observed in these monkeys appeared to be entirely reversible. All five suffered severe reductions in visual acuity and contrast sensitivity although flicker resolution was not affected. Visual loss was found to be irreversible, with degeneration of substantial numbers of retinal ganglion cells (companion paper) in those monkeys permitted to survive after the termination of exposure. None of the monkeys developed retinal microaneurysms or hemorrhages, major accepted signs of visual toxicity in CS2 exposed humans; thus, permanent visual loss may result from carbon disulfide exposure even in the absence of retinal vascular effects.

Animals↗

PubMed1985

Visual priming effects as a measure of short-term visual memory.

On each trial, subjects classified one of four letters as belonging to one of two categories. Visual priming occurs when the classification response is faster to a stimulus visually identical to a previous stimulus than to one identical only in name. Earlier experiments found no visual priming effects between stimuli separated by a stimulus of the same task but from the opposite classification category. Two of the five conditions in the present experiment varied the stimulus-response (S-R) contingencies in such a way that the penultimate but not the immediately preceding trial had the same contingencies. Only these two conditions gave evidence of the above type of visual priming. Visual priming was found, however, in almost all conditions when the intervening stimulus was from the same task and the same classification category. It is argued that a similarity of S-R contingency, and not simply stimulus similarity, is an important component of the visual priming effect.

Cognition↗

PubMedDate not supplied

[Visual evoked potentials in cases of damage to visual pathways at different levels].

Visual potentials induced with a checker pattern were studied in a group of patients with damage to the visual pathways at different levels, and were compared with similar potentials in 10 adult subjects without diseases. A statistically significant prolongation of latency of the main deflections (N1, P max and N2) was observed in the group of 14 patients with optic nerve damage, while in 10 patients with lesions above the chiasma different, often normal responses were obtained. High-grade deformity of visual potentials was observed in 2 cases of visual agnosia. The study of visual evoked potentials may be in the opinion of the authors, useful in cases of damage to the optic nerve, retina and cortical visual centres.

Adult↗

PubMedDate not supplied

[Formation of visual evoked potentials and development of visually guided behavior in the Ficedula hypoleuca nestling].

Age dynamics of evoked potentials (EPs) of Wulst area of the dorsal hyperstriatum (functional analogue of mammalian visual cortex) was investigated in 2-7 days old nestlings. EPs in response to light stimuli, with the duration and intensity imitating natural alimentary signals for 5-7 days-old nestlings, were recorded parallel with the behaviour. It was found that the development of the visual system in precocious nestlings became completed in postembryonal ontogenesis. The most essential changes in the parameters of visual EPs occur between 2.5 and 4 days of nest life. By the end of the 4-th day the EPs parameters resemble those of the definite EPs. During the same period the visually directed form of the alimentary behaviour appears for the first time. Both the visual EPs and the visually directed alimentary behaviour first appear in the ontogenesis in response to the second component of two-fold luminosity change--the natural signal of alimentary behaviour.

Animals↗

PubMed1983

[Visual fatigue during work associated with increased visual loading].

Visual perception is an important factor of human activity. The quality of production activity of the worker depends on its accuracy and speed. Representative groups of workers with various occupational activities, associated with considerable loading of visual system, were systematically examined by clinical and functional methods in the course of several years. A total of 765 subjects were examined, aged from 20 to 55 and a length of service from I to 25 years. The results reveal considerable alterations in visual system within one working day. The most general features of those alterations are as follows: elevation of the threshold of electric sensitivity towards the end of the working day, reduction of light-distinguishing and colour distinguishing sensitivity, the closest point of clear vision is removed father, unproper ergogram with an ascending course, reduction of fusion ability towards the end of the working day, etc. A great part of the subjects over the age of 40, were established to have uncorrected presbyopia, leading to high strain of accommodation and convergation, followed by visual fatigue. The adaptation of visual system to labour conditions is the best at the age range 25-35. The alterations in the visual function are far better manifested in the age group over 40. The determination of fatigue degree and the time of developing of the first alterations is of particular significance for the introduction of additional rest for rehabilitation.

Adult↗

PubMed1981

[Associative visual agnosia: role of the left hemisphere in visual perception (author's transl)].

Visual agnosia following ischaemic accidents of the left posterior cerebral artery is often associated with intellectual deficiencies, memory disorders, elementary perceptive disturbances and elements of visuoverbal disconnection, with the result that some authors reject the notion of visual agnosia. By using a relatively simple examination procedure it is, however, possible to clearly differentiate the various disturbances, as shown by the case of a right-handed 66-year-old man in whom this type of vascular accident occurred. Neither the reduced intellectual capacities nor the memory disorders can explain the differences observed in the treatment of visual stimuli, which was very disturbed, and the normal treatment of other types of stimulus. Elementary difficulties are not sufficient to prevent correct discrimination, as all tests of matching object, images, colours, and graphic signs were successfully accomplished. Identification was disturbed however: the patient could not show the use of objects presented visually, and this disorder is related to the visual characteristics of the stimuli, which excludes a simple visuogestural disconnection; results of tests of classifying types of object images, colours, and graphic signs were markedly abnormal. Naming of these stimuli was also affected, even when they were correctly identified; this results from the visuoverbal disconnection associated with the agnosia, but it is insufficient to account for it, as the patient could correctly use objects that had been wrongly named, but could not use those that had been poorly identified. This case, therefore, has enabled a visual identification disorder to be isolated independently from a discrimination problem, and visuoverbal or visuogestural disconnections. It is the significance of ths stimulus that is disturbed. In contrast, functional or categorical classification is respected in right temporo-occipital lesions. It is the individuality of a stimulus within a physical category which is disturbed.

Aged↗

PubMed1995

Delayed visual evoked potentials in adults after monocular visual deprivation by a dense cataract.

PURPOSE: To study the effect of monocular visual deprivation caused by dense unilateral cataracts in adults. METHODS: Visual evoked potentials have been recorded in 11 patients after removal of a dense unilateral cataract acquired in adulthood. These were compared with those from 8 control patients after removal of a mild lens opacity. RESULTS: Visual evoked potentials recorded on the first day after removal of a longstanding, dense, unilateral cataract showed a marked delay to stimulation of the operated eye compared to the unoperated eye. No delay was found in the operated or unoperated eye of control patients. Delays in the visual evoked potential returned to normal within approximately 3 months after surgery, with the exception of the two patients with the most longstanding cataracts in whom the delays persisted much longer. CONCLUSIONS: The adult central visual system is sensitive to visual deprivation caused by a longstanding, dense, unilateral cataract. The changes found may be important in understanding the causes of intractable diplopia, which sometimes occurs after the removal of such cataracts.

Adult↗