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PubMed2002

Visual field asymmetries and allocation of attention in visual scenes.

Single items such as objects, letters or words are often presented in the right or left visual field to examine hemispheric differences in cognitive processing. However, in everyday life, such items appear within a visual context or scene that affects how they are represented and selected for attention. Here we examine processing asymmetries for a visual target within a frame of other elements (scene). We are especially interested in whether the allocation of visual attention affects the asymmetries, and in whether attention-related asymmetries occur in scenes oriented out of alignment with the viewer. In Experiment 1, visual field asymmetries were affected by the validity of a spatial precue in an upright frame. In Experiment 2, the same pattern of asymmetries occurred within frames rotated 90 degrees on the screen. In Experiment 3, additional sources of the spatial asymmetries were explored. We conclude that several left/right processing asymmetries, including some associated with the deployment of spatial attention, can be organized within scenes, in the absence of differential direct access to the two hemispheres.

Adolescent↗

PubMed2004

Association of binocular lower visual field impairment, impaired simultaneous perception, disordered visually guided motion and inaccurate saccades in children with cerebral visual dysfunction-a retrospective observational study.

The principal pathways serving higher visual function comprise the dorsal stream and the ventral stream. The dorsal stream runs between the occipital lobes and the parietal lobes and subserves the ability to process the whole visual scene and carry out visually guided movement. The ventral stream runs between the occipital lobes and temporal lobe tissue and primarily subserves visual recognition and memory. These tissues are susceptible to dysfunction in children with brain damage. We report a series of 40 children in whom damage to the brain has led to a common symptom complex affecting vision. Lower visual field loss was frequently elicited. This was associated with impaired ability to make accurate visually guided movement (particularly of the lower limbs) accompanied by impaired simultaneous perception, and in some cases, with inaccurate saccades and in others, impaired perception of movement. These features are consistent with parietal/dorsal stream dysfunction. Difficulty recognising faces and problems with route finding (which are ventral stream functions) were also present in a number of the children. These visual difficulties can be manifest in the presence of normal visual acuity. Recognition of these problems leads to understanding of the child's visual difficulties and facilitates adaptation of curriculum delivery at school.

Adolescent↗

PubMed1987

Effect of defocus on visual field measurement.

Defocus increased visual field contrast thresholds for stimuli equal to or smaller than Goldmann perimeter target III (26 min arc diameter). Beyond 30 degrees-40 degrees from the centre of the visual field, defocus had little effect on contrast thresholds. For accurate clinical perimetry, ametropia and presbyopia should be corrected for small targets (less than or equal to target III) within 30 degrees-40 degrees of fixation with either a spectacle lens (if required power less than +/- 10 D) or a contact lens. Larger stimuli are little affected by defocus. Outside this central 30 degrees-40 degrees field, correction with contact lenses should be provided if fixation is poor due to ametropia. Scotomata for which no cause is evident should be further investigated to find whether they have a refractive basis.

Contact Lenses↗

PubMed1990

Locus of information in words and the right visual field effect.

The right visual field (RVF) advantage found for the identification or classification of words has usually been interpreted as evidence for left hemisphere language functions. It has more recently been explained as the result of the fact that the most informative part of the word, presumably the beginning, is in a region of better visual acuity. It is not clear from existing evidence that the beginnings of words are in fact more informative. The present study assessed the locus of information in words by deleting either the initial or terminal one or two letters. Subjects were required to generate a completion. Regardless of whether subjects were scored as correct for generating the original target word (as would be appropriate in a naming study) or for producing any legitimate word (as would be appropriate for a lexical decision study), the results indicated that most words have more information in the initial letters. Nevertheless, there are exceptions to this rule, and some words have more terminal information. Equal numbers of words with more initial information and with more terminal information were selected for two visual field studies in order to assess the effect of the locus of information on visual laterality. In neither a lexical decision study nor a naming study did locus of information affect the commonly observed right visual field superiority. Thus the distribution of information is not likely to be a major confounding variable in laterality studies employing horizontally presented words.

Adolescent↗

PubMed1981

Effect of auditory stimulation of subjects' chromatic visual fields.

The chromatic visual field of 14 subjects was measured while they heard a sound of 1000 Hz at 95 db during 3 min. Stimuli were produced by a monochromator. Visual threshold was lower under the influence of sound for red (lambda = 550 nm) and green (lambda = 610 nm) stimuli at 40 degrees, 45 degrees, and 50 degrees of temporal eccentricity.

Acoustic Stimulation↗

PubMed2005

Rehabilitation strategies for patients with homonymous visual field defects.

Homonymous visual field defects (HVFDs) are among the most common disorders that occur in brain damage, particularly after stroke. They lead to considerable disabilities, particularly with reading and visual exploration. A variety of different approaches, including optical aids and visual training techniques, have been examined for the rehabilitation of these HVFDs. Despite the considerable ingenuity that has been applied and anecdotal evidence that has accumulated, rigorously controlled trials that clearly establish efficacy of any method are lacking.

Brain Damage, Chronic↗

PubMed1999

Information from false statements concerning visual acuity and visual field in cases of psychogenic visual impairment.

BACKGROUND: If visual acuity (VA) and/or visual field (VF) is claimed to be worse than in reality, it can be difficult to estimate the actual VA/VF. This paper describes a method of proving malingering and of estimating the actual VA by statistical evaluation of the subjective responses to discrete visual stimuli. METHODS: VA is measured by using a Landolt or Snellen optotype with four possible directions. There are n (> or = 16) questions at each acuity level. Each direction of the optotype occurs with the same frequency. The sequence is not predictable. In testing the VF, the stimulus is presented in an unpredictable sequence but with the same frequency at each of four distinct locations outside the claimed field at the horizontal and the vertical meridian. The field is divided into four quadrants defined by the 45 degrees-225 degrees and 135 degrees-315 degrees meridians. The candidate is requested to search for the light. The target quadrant of the first eye movement is recorded. At each VA level, the distribution function of the binomial formula allows estimation of the probability Pc of < or = kc and > or = kc correct answers to n questions by mere accident. Regarding the VF, the direction of the first saccade at each stimulus presentation can be processed accordingly. RESULTS: If n = 32 and kc = 0,1,2, the chance P that this pattern is merely accidental is about 0.0001, 0.001, 0.007. Values of P < or = 0.01 strongly suggest that the answers were voluntarily wrong. Preference for the opposite direction can also point to psychogenic influence: If ko = 15,16,17,18, P is about 0.006, 0.002, 0.0006, 0.0002. CONCLUSION: Systematically false statements can yield valuable information about the actual visual functions.

Adult↗

PubMed2005

A child with epilepsy in whom multifocal VEPs facilitated the objective measurement of the visual field.

PURPOSE: We investigated whether visual field defects can be objectively evaluated by using multifocal visual evoked potential (multifocal VEP) in children with epilepsy in whom it is difficult to measure the visual field. METHODS: First, to determine normal waves in multifocal VEP, recording was performed by using a VERIS Junior Science (Mayo, Aichi, Japan) in 21 healthy children (21 eyes) consisting of 12 boys and nine girls aged 6 to 15 years (mean age, 11.4 years). Responses from eight sites in each subject were divided into four quadrants (superior and inferior temporal quadrants and superior and inferior nasal quadrants). In each quadrant, two response waves were grouped and averaged; peak latency and amplitude were used for assessment. In a child with epilepsy in whom kinetic or static perimetry was impossible, multifocal VEPs were recorded and compared with the peak latency and amplitude in the healthy subjects. RESULTS: In the 21 healthy children, no significant differences were observed in the peak latency or amplitude among four quadrants by one-way analysis of variance. Multifocal VEPs in the child with epilepsy showed abnormal waves in the right hemivisual field, which corresponded to the lesion observed with magnetic resonance imaging. CONCLUSIONS: The objective evaluation of visual field defects by using multifocal VEP may be useful in children with epilepsy in whom kinetic/static perimetry as a subjective examination is difficult.

Adolescent↗

PubMed1986

Effect of wearing chemical protective clothing in the heat on signal detection over the visual field.

Sensitivity for detecting visual signals distributed at various locations throughout the visual field was studied in 16 male subjects who were all exposed to two degrees of ambient heat (91 degrees F/61% RH; 55 degrees F/35% RH) while wearing the Army chemical protective clothing system; also to 70 degrees F/35% RH while wearing Army battle-dress uniform (fatigues). Response time for signal detection increased systematically and significantly with peripheralization of stimulus locations. It was most impaired in the superior and inferior visual field areas and least affected along the horizontal axis area. The data support previous results obtained using this task. Both the MOPP and the heat + MOPP exposure conditions produced highly significant systematic increases in response time to all signals; the worst performance occurred under the heat + MOPP combination. Implications for visual performance while wearing chemical protective gear are discussed.

Adolescent↗

PubMed1992

[The visual field of patients with pseudophakia using kinetic and automated perimetry].

One of the major benefits of pseudophakia is to maintain a good visual field. Visual field was therefore studied in 40 pseudophakic eyes using: 1. kinetic perimetry according to Goldmann using 3 tests: I1, I2, I4; 2. Automated perimetry. Insertion of a posterior chamber intraocular lens was performed in 85% of cases whereas the remaining 15% received an anterior chamber intraocular lens. Visual acuity was > 5/10 P2-P4 in all patients. The results showed a 15% reduction in the visual field compared to normal values. This reduction was concentric and harmonious but was more marked in internal isopters. This reduction was less marked with posterior chamber intraocular lenses. On the other hand, automated perimetry showed that global retinal sensitivity was decreased in pseudophakia, and this deficiency was more pronounced in the periphery.

Follow-Up Studies↗

PubMed1990

[The relation of fluorescein angiography in low tension glaucoma with retinal nerve fiber layer defect and visual field damage].

The fluorescein angiography, visual field and retinal nerve fiber layer defects (RNFLD) in 23 patients (35 eyes) with low tension glaucoma (LTG) showed that there was a marked positional correspondency between the fluorescein filling defect of the optic disc and the RNFLD (91.4%) or the visual field defect (77.1%). Besides, the rate of positional correspondent between the RNFLD and visual field defect was 80.0%. The study indicated that RNFLD and visual field defect of LTG are related to ischemia of the optic disc.

Adult↗

PubMed1993

The four-meter confrontation visual field test.

Confrontation visual fields have limited value in testing paracentral vision. We have used a four-meter confrontation test for several years at the Mayo Clinic for screening of the central field. This test can identify paracentral scotomas and macular sparing in a homonymous hemianopia. The optics of this technique parallel those of the two-meter tangent screen examination in which a scotoma is greatly enlarged by doubling the test distance. Although in common usage by some neuro-ophthalmologists, this simple technique is useful as an office screening device for evaluating paracentral vision.

Adult↗

PubMedDate not supplied

Modelling of orientation discrimination across the visual field.

In many visual tasks thresholds can be made equal across the visual field by increasing the size of peripherally presented stimuli by appropriate magnification. The parameter E2 represents the eccentricity at which foveal stimulus size must double in order to maintain performance equivalent to that at the fovea. We measured orientation discrimination for a set of line sizes at various eccentricities. Thresholds were successfully scaled by applying a scaling function estimated by a technique that requires no prior assumptions regarding the size of peripherally presented stimuli. E2 of 1.95 deg was found for orientation discrimination. From our results we were able to develop a single equation which predicts orientation discrimination thresholds for an average observer over a range of different eccentricities and line lengths.

Discrimination, Psychological↗

PubMed1995

Influence of posture on the visual field in glaucoma patients and controls.

The intra-ocular pressure rises when body position is changed from sitting to supine. This phenomenon occurs to the same extent in healthy people and glaucoma patients. The purpose of this preliminary study was to determine the effect of posture on the visual field. Visual fields of 15 eyes of 12 normal-tension glaucoma (NTG) patients, 16 eyes of 11 high-tension glaucoma (HTG) patients and 30 eyes of 26 healthy controls were measured in the upright and supine positions with program G1X on an Octopus swivel-arm perimeter. The delta mean defect (delta MD), that is MDupright-MDsupine, was calculated for each patient and compared among study groups. Whereas visual fields improved in healthy controls (delta MD = +0.45 dB), glaucoma patients showed a slight deterioration of the visual field after changing position from supine to upright (HTG: delta MD = -0.25 dB, NTG: delta MD = -0.24 dB). The difference between HTG and controls, as well as between NTG and controls, was statistically significant (p < 0.002, Student's t test). These findings indicate that in some glaucoma patients the regulatory mechanisms for blood supply in the optic nerve head are insufficient.

Adult↗

PubMed2004

[The analysis of various extent visual field defect in chronic glaucoma patients].

PURPOSE: To study the situation for the follow eye visual field defect of patients with severe visual field loss in 1 eye from chronic glaucoma,and to analyze the relative risk factors for visual field defect in such eyes. METHODS: The visual field defect scores of fellow eyes were calculated in 47 cases [primary chronic angle-closed glaucoma (PACG) 23 cases and primary open angle glaucoma (POAG) 24 cases] with severe visual field loss in 1 eye (visual field defect score > or = 12). The relations were analyzed between the visual field defect scores of fellow eyes and the visual acuity,the maximal and the mean intraocular pressure (IOP), ages, refraction, diagnosis, the last periods of glaucoma, gender and the anti-glaucoma surgery history. Spearman correlation analyse was used to estimated the correlation between the visual field defect scores of fellow eyes and the above factors. RESULTS: In the fellow eyes of the 23 cases PACG, 4 cases showed no visual field defect (score 0),5 cases showed the mild visual field defect (score 1-5), 7 cases showed the moderate visual field defect (score 6-11), 7 cases showed the severe or end-stage visual field defect (score 12-20). In the fellow eyes of the 24 cases POAG, 4 cases showed the mild visual field defect (score 1-5), 9 cases showed the moderate visual field defect (score 6-11), 11 cases showed the severe or end-stage visual field defect (score 12-20). The visual field defect score of fellow eyes in the last periods more than or equal to 10 years PACG group was significantly larger than that in the last periods less than 10 years PACG group (Z=2.8380, P=0.0224). The visual field defect score of fellow eyes in the mean IOP more than 18 mmHg PACG group was significantly larger than that in the mean IOP less than or equal to 18 mmHg PACG group (Z=1.9174, P=0.0276). The visual field defect score of fellow eyes in the anti-glaucoma surgery history POAG group was significantly larger than that in the non-anti-glaucoma surgery history POAG group (Z= 2.2377, P=0.0252). The significant positive correlation was found between the visual field defect scores and the mean IOP of the fellow eyes in the PACG group (r=0.4763, P= 0.0216),and the significant negative correlation was found between the visual field defect score and the visual acuity of the fellow eyes in the PACG group (r=-0.4416, P= 0.0349). CONCLUSION: Among the PACG with severe visual field loss in 1 eye, the visual field defect extent in the fellow eyes was related to the mean IOP, the last periods of PACG and the visual acuity of the fellow eyes. The visual field defect score was positively correlated with the mean IOP, and negatively correlated with the visual acuity of the fellow eyes.

Aged↗

PubMed1987

Chromaticity and achromaticity. Evidence for a functional differentiation in visual field defects.

In the visual field defects of 10 patients who had suffered lesions in the postgeniculate part of the primary visual projection, red-green discrimination and achromatic target detection was tested. In addition, 8 of these patients were tested for detection of red and green targets. Targets were presented on a low photopic achromatic background, so that the red and green targets differed from the background both in intensity and in wavelength, whereas the achromatic target differed in intensity only. Six patients showed evidence of discriminating between red and green targets, 5 patients could also detect the colour targets, but none could detect the achromatic one that was presented at the same retinal position. These results imply that wavelength and intensity information are treated differentially, and suggest that these patients possess residual colour-opponent channels that subserve the defective part of the visual field.

Color Perception↗

PubMed2004

No evidence of a lower visual field specialization for visuomotor control.

The lower visual field (loVF) has been hypothesized to demonstrate specialization for skilled, visually guided action. According to Danckert and Goodale, this visual field asymmetry indirectly suggests that the loVF has privileged connections to visuomotor networks within the dorsal visual pathway. Here we attempted to replicate the loVF advantage during the execution of a discrete aiming movement to targets of various widths (index of difficulty ranging from 1.5 to 5 bits). In addition, we employed trials in which vision of the target object was available or unavailable during the reaching movement to determine whether or not the purported visual field asymmetry reflects enhanced central planning (i.e., feedforward) or online control (i.e., feedback) processes. Reaching trajectories were examined for indicators of online amendments, and movement times and endpoint characteristics were examined to quantify possible visual field asymmetries in relative speed/accuracy trade-offs. In terms of reaching kinematics, it was found that vision of the target during the reaching movement resulted in greater online control of the reaching trajectory; however, no significant main effects or interactions involving visual field were observed. In other words, fixating in the upper or the lower region of peripersonal space did not influence the nature of reaching control (i.e., feedback vs. feedforward). Most importantly, our movement time and endpoint accuracy data elicited a robust speed/accuracy trade-off in both upper and lower regions of working space. Thus, and contrary to previous findings (such as those reported by Danckert and Goodale), the indices of difficulty coupled with the discrete aiming task used here did not elicit a lower visual field advantage for visually guided action.

Adult↗

PubMed2005

Multifocal visual evoked potential in nonorganic visual field loss.

OBJECTIVE: To evaluate the use of multifocal visual evoked potentials in the diagnosis of nonorganic visual field loss. METHODS: Five patients with unexplained visual field loss underwent full neuro-ophthalmic examination, Humphrey visual field testing, and multifocal visual evoked potential testing using the Accumap objective perimeter (ObjectiVision Pty Ltd, Sydney, Australia). RESULTS: In all 5 cases, the results of the ophthalmic examination did not correlate with the degree of visual field loss seen on Humphrey visual field testing. Multifocal visual evoked potentials testing showed essentially normal tracings. CONCLUSIONS: Multifocal visual evoked potentials may be useful in cases of difficult to prove functional visual field loss or in cases in which objective documentation of normal function is needed.

Adolescent↗