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PubMed2004

Attentional weighting: a possible account of visual field asymmetries in visual search?

Several previous visual search studies measuring reaction times have demonstrated scanning biases across the visual field (i.e. a tendency to begin a serial search in a particular region of space). In the present study, we measured visual discrimination thresholds for a target presented amongst distractors using displays that were short enough to greatly reduce the potential for serial (i.e. scanning) search. For both a motion and orientation task, subjects' performance was significantly better when the target appeared in the inferior, as compared to the superior, visual field (no differences were observed between left and right visual fields). These findings suggest that subjects may divide attention unevenly across the visual field when searching for a target amongst distractors, a phenomenon we refer to as 'attentional weighting'. To rule out the possibility that these visual field asymmetries were sensory in nature, thresholds were also measured for conditions in which subjects' attention was directed to the location of the target stimulus, either because it was presented alone in the display or because a spatial cue directed subjects' attention to the location of that target presented amongst distractors. Under these conditions, visual field asymmetries were smaller (or non-existent), suggesting that sensory factors (such as crowding) are unlikely to account for our results. In addition, analyses of set-size effects (obtained by comparing thresholds for a single target vs. the target presented amongst distractors) could be accounted for by an unlimited capacity model, suggesting that multiple stimuli can be processed simultaneously without any limitations at an early stage of sensory processing. Taken together, these findings suggest the possible existence of biases in attentional weighting at a late stage of processing. The bias appears to favor the inferior visual field, which may arise from the fact that there is more ecologically-relevant information in this region of space.

Attention↗
PubMed2003

Posture and mental task performance when viewing a moving visual field.

We investigated the characteristics of standing posture and performance of concurrent cognitive tasks in subjects confronted by whole field visual motion. Movements of the head and centre of pressure (COP) were recorded in 12 subjects who performed modified Brooks spatial and verbal tasks when in quiet stance viewing a chequerboard pattern, planar, visual field, moving with uniform velocity (25 degrees /s, 50 degrees /s and 76 degrees /s). Eight subjects were also tested seated to control for the effect of stance. Task load was monitored by heart rate and eye movements were recorded to ensure viewing compliance. Subjects rated their quotidian susceptibility to visual disorientation on a validated scale. In both lateral and antero-posterior directions there were small amplitude but significant increases in COP sway path length and standard deviations of both COP and head sway during exposure to visual motion in proportion to visual flow speed. Performing cognitive tasks during visual motion attenuated sway S.D. The effects on sway of task and visual flow were independent. Visual motion induced a slight tilt and turn of the head and body in the direction of flow together with slight neck flexion. Errors on both verbal and spatial tasks increased >250% during visual motion both when standing and when seated. Ratings of subjects' susceptibility to disorientation were un-related to either verbal or spatial task error rates. A current hypothesis is that the enhancement of sway by visual motion is destabilisation. We propose an alternative explanation that sway enhancement could be exploratory 'testing of the ground' movements to check for self motion. Hence decrease in sway magnitude during a cognitive task could be caused by a reduction in exploratory movement because attention is diverted from postural control to a secondary task. Mere passive viewing of a moving visual field may interfere with cognitive tasks possibly because the threat of disorientation by whole field motion diverts attentional resources.

Adult↗
PubMed1993

Oculokinetic perimetry compared with Humphrey visual field analysis in the detection of glaucomatous visual field loss.

The ability of oculokinetic perimetry (OKP) to detect glaucomatous central visual field loss was assessed by comparison with the results of Humphrey visual field analysis (HVFA) in a group of patients attending a glaucoma clinic. Fifty-six patients with stable visual fields and good reliability indices on previous automated perimetry examinations underwent programmes 24-1 or 24-2 of the Humphrey visual field analyser and the results compared with those of a field test using a hand-held OKP chart. Forty-three patients had a glaucomatous visual field defect demonstrated by HVFA, and 35 showed a defect to OKP. Thirteen patients were shown to have normal fields on HVFA, and in 21 patients the OKP test was normal. Comparison of the two test results showed that of the 35 patients with abnormal OKP tests, in 26 the result was a true positive (HVFA also abnormal) and in 9 a false positive (HVFA normal). In the 21 patients with negative OKP tests the results were judged false negatives in 13 (HFVA showed glaucomatous visual field loss) while in 8 they were true negatives (HVFA normal). Therefore the sensitivity of OKP for the detection of glaucomatous visual field loss was 60.5% and the specificity for the identification of individuals with glaucomatous visual field loss was 61.5%. In the 26 patients with true positive results there were 36 eyes with positive OKP charts corresponding to defects on HVFA. Correlation of the number of defects on OKP with the mean deviation and corrected pattern standard deviation of their respective HVFA charts showed a near linear correlation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2004

Sensitivity and specificity of the 76-suprathreshold visual field test to detect eyes with visual field defect by Humphrey threshold testing in a population-based setting: the Thessaloniki eye study.

PURPOSE: To evaluate the screening performance of the 76-Suprathreshold (76-STHR) visual field test to detect eyes with visual field defect (VFD) as measured by Humphrey threshold testing in a population-based setting. DESIGN: Cross-sectional study. METHODS: All 88 subjects who agreed to participate in the pilot phase of the Thessaloniki Eye Study were included. Participants underwent a 76-STHR visual field test followed by a 30-full threshold (30-2 FTHR) test (Humphrey field analyzer). One eye/subject was randomly selected and included in the analysis. Sensitivity and specificity rates of the 76-STHR to detect eyes with VFD by the 30 to 2 FTHR test were calculated. RESULTS: When eyes with borderline results in the 30 to 2 FTHR test were classified as having a VFD, sensitivity rates of the 76-STHR to detect eyes with VFD by the 30 to 2 FTHR were 85.2%, 77.8%, and 74.1%, whereas specificity rates were 70%, 78%, and 86%, depending on the cutoff used for the 76-STHR. CONCLUSIONS: The 76-STHR test showed high sensitivity and low false-negative results at the "at least one point missed" cutoff level criterion to detect eyes with visual field defect by Humphrey threshold testing in a population-based setting. This criterion should be used when screening in a population-based study setting. By contrast, the 76-STHR would not be the appropriate screening test in a primary care setting with limited resources.

Aged↗
PubMed1991

The effects of weighting the "mean defect" visual field index according to threshold variability in the central and midperipheral visual field.

Two visual field indices, the mean defect (MD) of Flammer and the mean deviation (MD) of Heijl, have found wide acceptance among perimetrists. We compared these indices in 169 visual fields from normal- and high-tension glaucomatous eyes. Visual field damage in these eyes varied from slight to severe. In computations of the mean deviation index, the threshold values are weighted by the threshold deviations obtained from normal eyes as a function of eccentricity. However, the present study shows that the differences between the two indices in the population studied are negligible. Thus, subsequent interpretation is not affected by the choice of index, and the two MD indices may be considered to be interchangeable for the types of visual fields used in this study and for program-G1 examinations carried out using Octopus automated perimeters. Since we found smaller increases in local intersubjective fluctuations as a function of eccentricity in 274 normal visual fields as compared with results published by others, caution is indicated for interpretation of the visual field using probability weighting.

Humans↗
PubMed2000

Visual field progression in patients with initially unilateral visual field loss from chronic open-angle glaucoma.

PURPOSE: To investigate visual field progression in patients with initially unilateral glaucomatous visual field loss, and to determine risk factors for progression. DESIGN: Retrospective observational case series. PARTICIPANTS: Forty-eight consecutive patients with primary open-angle glaucoma, pseudoexfoliative glaucoma, or pigmentary glaucoma, seen over an 18-month period, who initially had unilateral visual field loss as defined by use of modified Anderson criteria. Patients were followed with standard Humphrey perimetry for a minimum of 2 years. METHODS: Progression was defined by use of modified Anderson criteria, and Advanced Glaucoma Intervention Study (AGIS) and Collaborative Initial Glaucoma Treatment Study scores. MAIN OUTCOME MEASURE: Visual field progression. RESULTS: Three patients (6.2%) had fellow eye progression over a mean follow-up of 76 months and duration of disease of 8.7 years. Fellow eye progression correlated with progression of the first-affected eye (P = 0.044). Ten patients (21%) had progression of the first-affected eye; these eyes had a larger initial cup/disc ratio compared with stable eyes (P = 0.041). Increasing initial AGIS score was associated with progression (P: = 0.003). Kaplan-Meier survival analysis estimated the risk of progression at 5 years to be 25% in first-affected eyes and 7.2% in fellow eyes. CONCLUSIONS: In this population, the risk of fellow eye progression in patients with initially unilateral visual field loss from open-angle glaucoma is low. Progression is higher in eyes with visual field loss at initial testing, and the risk of progression increases as the level of initial visual field loss increases.

Adult↗
PubMed2005

Normal visual field test results following glaucomatous visual field end points in the Ocular Hypertension Treatment Study.

OBJECTIVE: To compare the occurrence of normal visual field (VF) test results following 2 vs 3 consecutive, abnormal, reliable test results in the Ocular Hypertension Treatment Study. METHODS: The Ocular Hypertension Treatment Study is a prospective, multicenter follow-up study as part of a longitudinal randomized clinical trial. Sixty-four (68 eyes) of 1636 participants developed a VF primary open-angle glaucoma (POAG) end point. We compared the proportion of normal VF test results after a VF POAG end point among eyes whose VF abnormality was confirmed by 2 (n = 9 eyes) vs 3 (n = 59 eyes) consecutive, abnormal, reliable VF test results. RESULTS: The proportion of VF test results that were normal subsequent to a VF POAG end point in eyes whose abnormality was confirmed by 2 consecutive, abnormal, reliable test results was significantly higher (73 [66%] of 110) compared with eyes whose abnormality was confirmed by 3 consecutive, abnormal, reliable test results (46 [12%] of 381) (P = .01). CONCLUSIONS: A VF POAG end point confirmed by 3 consecutive, abnormal, reliable VF test results appears to have greater specificity and stability than either 1 or 2 consecutive, abnormal, reliable VF test results. However, some eyes whose VF POAG end point was confirmed by 3 consecutive, abnormal, reliable test results nonetheless had 1 or more normal test results on follow-up.

Adult↗
PubMed1995

Determining progressive visual field loss in serial Humphrey visual fields.

PURPOSE: To evaluate the three commercially available computerized statistical algorithms for determining progression of glaucomatous field loss in serial Humphrey fields. METHODS: Serial Humphrey fields of 102 ocular hypertensive and glaucomatous eyes were analyzed by linear regression analysis of Statpac, glaucoma change probability and Progressor Programme, and the results compared with a retrospectively determined clinical outcome. RESULTS: Linear regression analysis of Statpac identified progression in 11 field series, glaucoma change probability identified progression in 23 field series, and Progressor Programme identified progression in 27 field series. Clinical outcome identified much less-progression than any of the three algorithms, determining that only seven eyes showed deterioration. There was a wide variation of results from analysis of the same group of field series by the three different algorithms. In contrast to the other two algorithms, which detected progression in similar percentages of both ocular hypertension and glaucoma field series. Progressor Programme detected progression predominantly in glaucoma field series. CONCLUSIONS: There was a high degree of variability among the three different algorithms for determining visual field progression, and none of them correlated well with clinical impression.

Algorithms↗
PubMed1994

Detection of visual field deficits and visual neglect with computerized light emitting diodes.

A computer test for visual field deficits and visual neglect was developed and evaluated by testing 63 patients with brain damage. This computer test controls the sequence of unilateral or bilateral lights series, and stores the responses. Test results are compared to clinical and ophthalmological tests and neuropsychological assessment. Visual field deficits were present in 17 patients on the computerized test, in 16 patients on ophthalmological test, and in 13 patients on clinical examination. Neglect was present in 12 patients on the computerized test, and in 10 patients on the neuropsychological assessment. Eighteen patients had mixed disorder (hemianopia and neglect). Results of the chi 2 statistic confirm the greatest correlation between the computerized test and the ophthalmological (phi = 0.93; p < 0.001) and neuropsychological (phi = 0.90; p < 0.001) tests. Correlation between the computerized test and the clinical examination was poorer (phi = 0.85; p < 0.001). The computerized test makes it possible to detect mixed disorder with the same tool, during the same examination.

Adolescent↗
PubMed1995

Human cortical regions activated by wide-field visual motion: an H2(15)O PET study.

1. Several areas in the monkey dorsal visual pathway, including the dorsal part of the medial superior temporal area, have been found to contain cells responding to movements of a wide visual field and are suggested to be involved in analyzing self-induced motion information. In the present study, positron emission tomography was used to localize human cortical regions responding to wide-field visual motion. Changes in regional cerebral blood flow (rCBF) were measured when subjects maintained fixation and viewed low-contrast (0.15 log units brighter than the background) dots subtending 80 x 80 degrees and moving either coherently or incoherently. Brain foci were localized after activity in a fixation-only paradigm was subtracted from that in the two moving dot paradigms. 2. Both the coherent and incoherent movements significantly activated the primary/secondary visual cortex and surrounding visual areas in the cuneus and superior occipital gyrus. Subtraction of images between the coherent and incoherent movements showed that the activity caused by the two types of movement was comparable in these early visual cortical regions. 3. In the lateral occipitotemporoparietal cortex, the coherent movement specifically activated two separate areas; a posterior focus was located at the border of the right occipitotemporal gyri, and a dorsoanterior focus was located bilaterally in the temporoparietal cortex. The incoherent movement did not activate these regions. 4. A fine anatomic localization using individual magnetic resonance images was performed for the bilateral activation in the temporoparietal cortex, which was found to be located mainly in the depth of the inferior parietal lobule and a small portion of the superior and middle temporal gyri. 5. Both the coherent and incoherent movements activated a part of the superior parietal lobule located within the intraparietal sulcus (Brodmann area 7). The bilateral foci activated by the coherent movement were located more anteriorly than the focus activated by the incoherent movement. Subtraction images between the coherent and incoherent movements, however, did not reveal any significant rCBF increases in the superior parietal lobule. 6. Several other cortical regions known to be involved in visuospatial and visuomotor functions were also activated by the coherent movement, including the frontal eye field (Brodmann area 8) and premotor cortex (Brodmann area 6) in the frontal lobe. 7. The posteriorly located activation at the border of occipito-temporal gyri corresponds to the homologue of the middle temporal area reported in previous activation studies using small to medium-sized motion stimuli. The bilateral activation in the inferior parietal lobule appeared to rely on wide-field motion stimulation.

Adult↗
PubMed2000

[The development of a computer-based visual field analyzer].

Visual field is one of the important visual functions; it is the extent of the visual field defect that can be employed in judging whether the visual function is impaired. The rapid achievements in computer technologies do provide an impulse for improvement of visual field detection, making possible the automatic, rapid, accurate, detailed and large-scaled visual field detection. This paper gives a thorough description about development of the visual field analyzer, model TEC-2A, which is based on PC windows platform, Visual Basic software developing tool, ISA peripheral circuits, standard Goldmann visual field half-ball and standard stimulus.

Adolescent↗
PubMed2004

Integrated visual fields: a new approach to measuring the binocular field of view and visual disability.

BACKGROUND: We have developed a method of quantifying the central binocular visual field by merging results from monocular fields (Integrated visual field). This study aims to compare the new measure with the binocular Esterman visual field test in identifying patients with self-reported visual disability. METHODS: Forty-eight patients with glaucoma each recorded Humphrey 24-2 fields for both eyes and an Esterman on the same day, and each completed a binary forced-choice questionnaire relating to perceived visual disability. Computer software merged sensitivity values from monocular fields to generate an integrated visual field and a related score of the number of defects at the <10 dB and <20 dB level. Receiver operating characteristic (ROC) analysis was used to compare the integrated visual field score and the Esterman disability score with individual responses to the questions on perceived difficulty with visual tasks. RESULTS: Comparison of areas under ROC curves revealed that a score based on the integrated visual field was generally better (median area: 0.79) than Esterman scores (median area: 0.70) in classifying patients with or without a self-reported perceived difficulty with visual tasks. CONCLUSIONS: The integrated visual field offers a rapid assessment of a glaucoma patient's binocular visual field without extra perimetric testing. As compared to an actual binocular field test (Esterman), the integrated visual field provides a better prediction of a glaucoma patient's perceived inability to perform certain visual tasks.

Adult↗
PubMed1989

Visual field in hysteria-reliability of visual field by Goldmann perimetry.

Four cases with hysterical amblyopia in youngsters under 15-year-old showed the poor reproducibility of visual field, that is, when the same target was moved from the periphery toward the fixation ten times along the same meridian during the same examination, the position of the plotted points were rather variable. The range of variation was measured from the innermost point to the outermost one, after the two first points were omitted because points first detected were usually far from the others. The variation of cases measured by this method was compared with that of normal persons. Results were as follows; 1. in normal person, the mean value of its range was 5.5 degrees in first decade and 4.2 degrees in second to seventh decade; 2. patients with psychogenic visual disturbances showed a variability of 14.2 degrees, and this was significantly different from normal (p less than 0.01). These results suggest that this convenient method was helpful for diagnosis of hysteria. It should also be remembered that when we evaluate the visual field, changes under 4 degrees are probably not significant.

Adolescent↗
PubMed2000

Comparison of visual field progression in patients with normal pressure glaucoma between eyes with and without visual field loss that threatens fixation.

AIM: To compare the frequency and site of visual field progression and changes in visual acuity in patients with normal pressure glaucoma (NPG) with and without pre-existing visual field loss. METHOD: Patients with normal tension glaucoma were selected who had at least 10 visual fields over 5 or more years of follow up and no other condition that might influence the visual field or visual acuity. Alternate left and right eyes were selected from patients in random order. These eyes were then subdivided according to visual field defect threatening fixation, visual field defect not threatening fixation, and no visual field defect (fellow eyes). Eyes were defined as showing a threat to fixation according to the presence of a visual field defect involving one of more of four paracentral visual field locations. Pointwise linear regression analysis was applied to each visual field series using PROGRESSOR software. Progression of visual field loss was defined as the appearance of a regression slope 1 dB per year or more with a significance of p<0.01, which remained consistent with the addition of two of three successive visual fields to the series. The number of patients showing progression and the number where progression occurred in one of the four paracentral visual field locations was noted. The number of eyes losing two or more lines of Snellen visual acuity over the follow up period was also noted. RESULTS: 174 eyes of 174 patients were selected. 106 eyes had visual field loss threatening fixation, 46 eyes had visual field loss that did not threaten fixation, and 22 were fellow eyes with normal visual fields. The median follow up was 7.2 years. Eight eyes (36.4%) in the "normal visual fields" group, 31 eyes (67.4%) in the "visual field loss away from fixation" group, and 87 eyes (82.1%) in the "threat to fixation" group showed progression in any part of the visual field. Two eyes (9.1%) in the "normal visual fields" group, nine eyes (19.6%) in the "visual field loss away from fixation" group, and 45 eyes (42.5%) in the "threat to fixation" group showed progression at "threat to fixation". The Cox proportional hazards regression model showed an increased risk of progression at any part of the visual field for female sex and a decreased risk for eyes with normal visual fields. For progression at threat to fixation this model showed an increased risk with pre-existing threat to fixation. Eyes from older patients and those that went on to have progressive visual field loss at fixation were more likely to lose two lines of Snellen visual acuity over the follow up period. CONCLUSION: Since 20-30% of previously field damaged eyes and over 60% without prior field loss fail to demonstrate progressive visual field damage over a long follow up it is recommended that normal pressure glaucoma patients be monitored for progression and that potentially harmful therapy be withheld until progression is demonstrated. Although the presence of visual field loss that threatens fixation does not constitute an increased risk of visual field progression it does indicate an increased risk of further loss of visual field close to fixation which is in turn associated with loss of central acuity. In the light of this finding, patients with visual field loss that threatens fixation should be managed more aggressively.

Aged↗
PubMed1980

Regional variation in the representation of the visual field in the visual cortex of the Siamese cat.

In Siamese cats, many ganglion cell fibers from the temporal retina misproject to the contralateral hemisphere; as a result, each lateral geniculate nucleus contains an abnormally large representation of the ipsilateral visual field. The manner in which the visual cortex processes this aberrant visual information has been examined in several previous studies. In some Siamese cats, the region of the 17/18 border was found to contain an extensive, systematic map of the ipsilateral field, while in other animals no such map was found, and the 17/18 border appeared to represent the zero meridian of azimuth (as in normal cats). These results have led to the suggestion that there are two distinct types of Siamese cat ("Boston" and "Midwestern") which can be distinguished on the basis of cortical topography and the anatomical organization oif the geniculocortical pathway. In the present study, we have recorded from four Siamese cats in order to examine the visual field map in the region of the 17/18 border; in each cat we recorded at anterior coronal levels corresponding to the representation of the lower visual field, and also at more posterior levels near the horizontal meridian representation. In all of the animals we found that the anterior penetrations (corresponding to mean receptive field elevations inferior to -7 degrees) yielded 15-20 degrees of ipsilateral field representation at the 17/18 border; however, the posterior, horizontal meridian penetrations (with mean elevations from +1 degrees to -4 degrees) showed excursions of only about 5 degrees into the ipsilateral field. This large difference in the representation of azimuth was not due to rotation of the eyes during our recording sessions. The finding of appreciable differences in the amount of ipsilateral field represented at different anterior-posterior levels of the same animal might lead to the suggestion that there are not two distinct populations (or types) of Siamese cat with regard to the cortical map of the ipsilateral field. Rather, we raise the possibility that Siamese cats form one population in which there is a continuous variation in the extent of ipsilateral field represented in the cortex.

Animals↗