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At least 19 recordsLinked to original sources
PubMed1997

Visual impairment in Australia: distance visual acuity, near vision, and visual field findings of the Melbourne Visual Impairment Project.

PURPOSE: To describe the age-specific and gender-specific rates of blindness and visual impairment in urban adults aged 40 years and older. METHODS: A population-based sample of residents was recruited. Presenting and best-corrected distance visual acuities were assessed. Functional near vision was measured at each participant's preferred distance. Visual field examination was performed with a Humphrey Field Analyzer (HFA); those unable to perform the field analyzer test attempted a Bjerrum screen or confrontation field. RESULTS: The study population comprised 3,271 residents (83% of eligible) from ages 40 to 98 years; 54% were women. Overall, 56% of the study population wore distance correction; this was significantly lower in men but higher in the older age groups. Age-adjusted rates of blindness were 0.066% in men and 0.170% in women. Vision with current correction improved after refraction by gender and age. Direct age-standardized rates of functional near vision did not vary significantly by gender. Forty-six people had significant visual field loss in their better eye. The proportion of participants with constriction of the visual field to within 20 degrees of fixation was similar for men and women when controlled for age (odds ratio, 0.81; 95% confidence interval, 0.44 to 1.49) but increased significantly with age controlled for gender. Visual field abnormalities were detected in 548 right eyes (17%) and 533 left eyes (16%). CONCLUSIONS: Although overall rates of blindness because of visual acuity loss were relatively low, nearly three times more people had visual impairment because of visual field loss than visual acuity loss. These results highlight the need to target blindness prevention programs to the aging population, with a special emphasis on women.

Adult↗
PubMed1991

Aurally aided visual search in the central visual field: effects of visual load and visual enhancement of the target.

Visual search performance was examined in a two-alternative, forced-choice paradigm. The task involved locating and identifying which of two visual targets was present on a trial. The location of the targets varied relative to the subject's initial fixation point from 0 to 14.8 deg. The visual targets were either presented concurrently with a sound located at the same position as the visual target or were presented in silence. Both the number of distractor visual figures (0-63) present in the field during the search (Experiments 1 and 2) and the distinctness of the visual target relative to the distractors (Experiment 2) were considered. Under all conditions, visual search latencies were reduced when spatially correlated sounds were present. Aurally guided search was particularly enhanced when the visual target was located in the peripheral regions of the central visual field and when a larger number of distractor images (63) were present. Similar results were obtained under conditions in which the target was visually enhanced. These results indicate that spatially correlated sounds may have considerable utility in high-information environments (e.g., piloting an aircraft).

Adult↗
PubMed2005

Influence of auditory-verbal, visual-verbal, visual, and visual-visual processing speed on reading and spelling at the end of Grade 1.

This study examined cognitive processing speed through four modalities (auditory-verbal, visual-verbal, visual, and visual-visual) at the end of Grade 1 and how it influences reading and spelling. The subjects were 124 French-speaking children, selected for their contrasting performance on reading and spelling tasks. The children in the first group (N=69) were average readers; the second group of children (N=55) performed worse or much worse on all reading and spelling tasks. The experimental design consisted of a set of 10 tasks administered in two sessions. The major findings reveal that: (1) the children with reading difficulties displayed low and slow performance on most cognitive tasks, whatever the modality; (2) auditory-verbal and visual-verbal processing speed significantly predicted written language, which was not the case with the visual modalities; and (3) that visual problems did not appear to be a potential cause of reading problems in most delayed readers. The findings also confirm the independence of phonological and naming-speed skills in reading development and reading impairment.

Age Factors↗
PubMed2000

[Pattern visual evoked potentials visual acuity--the evaluation of visual acuity of less than 0.1].

PURPOSE: We previously developed a new method for estimating objective visual acuity by means of pattern visual evoked potentials (PVEP). In this study, this method was applied to the evaluation of visual acuity of 0.05 and 0.01. METHODS: Ten subjects with visual acuity of 0.05 and ten normal subjects with visual acuity of 0.01 were examined. The visual acuity of the subjects was decreased step by step by means of plus spherical lenses of increasing power. In the PVEP study, the stimulus consisted of black and white checkerboards with a visual angle of 8 degrees (central stimulus) and a global field with a 5 degrees central circular scotoma (peripheral stimulus), contrast level of 15%, and a frequency of 0.7 Hz. One hundred PVEP responses were averaged per session. We reported that there was a linear relation between log subjective visual acuity of 0.1-1.0 and log check size of the patterns with PVEP. In reference to that, the check sizes of the patterns were estimated at 66' with visual acuity of 0.05, and 107' with visual acuity of 0.01. Each visual acuity was then used with other check sizes of three patterns. RESULTS: With central stimulus the P100 components of O1, O2, and Oz were recorded with 66' and 82' patterns at visual acuity of 0.05(central stimulus). The P100 components of O1, O2, and Oz were 107', 137' and 161' at visual acuity of 0.01(central stimulus). There was no P100 component at visual acuity of 0.05 and 0.01(peripheral stimulus). CONCLUSION: This method of PVEP is a useful tool as an objective estimation of visual acuity less than 0.1 and is presumed to stimulate preferentially the X retinal ganglion cell to parvocellular pathway.

Adult↗
PubMed2005

The use of visual feedback is independent of visual awareness: evidence from visual extinction.

Milner and Goodale (The visual brain in action, Oxford Press, 1995) made a distinction between vision for perception and vision for action. In contrast to perception, many action tasks have strict temporal constraints, which can only be met if the visual information is relayed directly to the motor system without first passing through a conscious decision making process. Milner and Goodale therefore predict that visual stimuli do not have to reach visual awareness in order to guide rapid motor responses. Online visual feedback provides a good example of visual information that is used under tight temporal constraints to guide rapid motor responses. Online visual feedback provides information about the position of the moving limb. This information can be used to improve the accuracy of our movements. If vision for action operates independently of visual awareness, visual feedback should be beneficial even if the subject is unaware of this information. We tested this prediction in a patient (V.E.) with left-sided visual extinction, a condition in which a visual stimulus typically fails to reach awareness if a second stimulus is presented simultaneously at a more rightward location. V.E. was asked to point towards a central target with his left hand. In some trials a light-emitting diode (LED) provided brief visual feedback from the moving hand. However, in the majority of trials, V.E. was unaware of this LED, due to his extinction. His performance was nevertheless significantly better when visual feedback was present, regardless of whether or not the information was available for verbal report. We conclude that visual awareness is not essential for the effective use of online visual feedback.

Aged↗
PubMed1996

Baseline, visual deprivation and visual stimulation 99TCm-HMPAO-related changes in visual cortex can be detected with a single-head SPET system.

To determine the sensitivity of 99TCm-hexamethylpropylene amine oxime (99TCm-HMPAO) and a single-head SPET (single photon emission tomography) system in the detection of perfusion changes in the visual cortex due to different visual conditions, six normal healthy volunteers were studied under conditions of visual deprivation (blindfolded), visual stimulation (stroboscopic light) and baseline (dim light and eyes open). Visual cortex/whole-brain activity ratios, and the percentage of activity change between the different visual conditions were calculated after three-dimensional realignment of the images. The activity in the visual cortex was higher during visual stimulation than during the visual deprivation (P = 0.002, 17.6 +/- 8.6% increase) and baseline conditions (P = 0.009, 8.8 +/- 5.6% increase). Furthermore, the activity in the visual cortex was lower during the visual deprivation than in the baseline condition (P = 0.001, 8.1 +/- 2.9% decrease). 99TCm-HMPAO SPET, even with a single-head system, is capable of detecting changes in rCBF in the striate cortex, not only between conditions of visual stimulation and deprivation, but also between these two conditions and the baseline state.

Adult↗
PubMedDate not supplied

Visual memory, visual imagery, and visual recognition of large field patterns by the human brain: functional anatomy by positron emission tomography.

We measured the regional cerebral blood flow (rCBF) in 11 healthy volunteers with PET (positron emission tomography). The main purpose was to map the areas of the human brain that changed rCBF during (1) the storage, (2) retrieval from long-term memory, and (3) recognition of complex visual geometrical patterns. A control measurement was done with subjects at rest. Perception and learning of the patterns increased rCBF in V1 and 17 cortical fields located in the cuneus, the lingual, fusiform, inferior temporal, occipital, and angular gyri, the precuneus, and the posterior part of superior parietal lobules. In addition, rCBF increased in the anterior hippocampus, anterior cingulate gyrus, and in several fields in the prefrontal cortex. Recognition of the patterns increased rCBF in 18 identically located fields overlapping those activated in learning. In addition, recognition provoked differentially localized increases in the pulvinar, posterior hippocampus, and prefrontal cortex. Learning and recognition of the patterns thus activated identical visual regions, but different extravisual regions. A surprising finding was that the hippocampus was also active in recognition. Recall of the patterns from long-term memory was associated with rCBF increases in yet different fields in the prefrontal cortex, and the anterior cingulate cortex. In addition, the posterior inferior temporal lobe, the precuneus, the angular gyrus, and the posterior superior parietal lobule were activated, but not any spot within the occipital cortex. Activation of V1 or immediate visual association areas is not a prerequisite for visual imagery for the patterns. The only four fields activated in storage recall and recognition were those in the posterior inferior temporal lobe, the precuneus, the angular gyrus, and the posterior superior parietal lobule. These might be the storage sites for such visual patterns. If this is true, storage, retrieval, and recognition of complex visual patterns are mediated by higher-level visual areas. Thus, visual learning and recognition of the same patterns make use of identical visual areas, whereas retrieval of this material from the storage sites activates only a subset of the visual areas. The extravisual networks mediating storage, retrieval, and recognition differ, indicating that the ways by which the brain accesses the storage sites are different.

Adult↗
PubMed2006

Crossmodal audio-visual interactions in the primary visual cortex of the visually deprived cat: a physiological and anatomical study.

Blind individuals often demonstrate enhanced non-visual perceptual abilities. Neuroimaging and transcranial magnetic stimulation experiments have suggested that computations carried out in the occipital cortex may underlie these enhanced somatosensory or auditory performances. Thus, cortical areas that are dedicated to the analysis of the visual scene may, in the blind, acquire the capacity to participate in other sensory processing. However, the neural substrate that underlies this transfer of function is not fully characterized. Here we studied the synaptic and anatomical basis of this phenomenon in cats that were visually deprived by dark rearing, either early visually deprived after birth (EVD), or late visually deprived after the end of the critical period (LVD); data were compared with those obtained in normally reared cats (controls). The presence of synaptic and spike responses to auditory stimulation was examined by means of intracellular recordings in area 17 and the border between areas 17 and 18. While none of the cells recorded in control and LVD cats showed responses to sound, 14% of the cells recorded in EVD cats showed both subthreshold synaptic responses and suprathreshold spike responses to auditory stimuli. Synaptic responses were of small amplitude, but well time-locked to the stimuli and had an average latency of 30+/-12ms. In an attempt to identify the origin of the inputs carrying auditory information to the visual cortex, wheat germ agglutinin-horseradish peroxidase (WGA-HRP) was injected in the visual cortex and retrograde labeling examined in the cortex and thalamus. No significant retrograde labeling was found in auditory cortical areas. However, the proportion of neurons projecting from supragranular layers of the posteromedial and posterolateral parts of the lateral suprasylvian region to V1 was higher than that in control cats. Retrograde labeling in the lateral geniculate nucleus showed no difference in the total number of neurons between control and visually deprived cats, but there was a higher proportion of labeling in C-laminae in deprived cats. Labeled cells were not found in the medial geniculate nucleus, a thalamic relay for auditory information, in either control or visually deprived cats. Finally, immunohistochemistry of the visual cortex of deprived cats revealed a striking decrease in pavalbumin- and calretinin-positive neurons, the functional implications of which we discuss.

Acoustic Stimulation↗
PubMed1996

Plasticity in the adult visual cortex: implications for the diagnosis of visual field defects and visual rehabilitation.

It has recently been shown that, contrary to long-held beliefs, sensory and motor maps are not stable in the adult cerebral cortex. Alteration of input from the periphery results in changes in topography in the cortex, including the primary visual cortex. Mechanisms involved consist mainly of reshaping the receptive field of cortical cells and increasing the sensitivity of deprived cells in the visual cortex. Cortical plasticity allows the brain to adapt to background modifications or to damage of the nervous system. It also underlies learning and attention processes. Cortical changes occurring after focal visual differentiation modify visual perception by filling in visual field defects with information from the area surrounding the scotoma. This modification causes affected subjects to ignore or underestimate their defects. With visual field defects, cortical plasticity also causes distortion in spatial perception. Although the effects of cortical plasticity are prominent in neuro-ophthalmological daily practice, they are usually unrecognized or greatly underestimated. These effects cause delay in recognizing visual field defects, and hence in receiving therapy, while affecting the results of some procedures for testing the visual field. Affected individuals who are unaware of their defects may have increased difficulty in coping with activities in everyday life. Up to now, phenomena related to plasticity in the visual system have been investigated mainly by psychophysicists and neurophysiologists. It is essential to start considering the various effects of cortical reorganization in clinical practice. It is especially important to introduce into clinics the concept of dissociation between actual and perceived defects in the visual field, resulting from the filling-in process, and the need to measure it. This dissociation should also be demonstrated to the affected subjects.

Adult↗
PubMed2006

Discordance between subjective perimetric visual fields and objective multifocal visual evoked potential-determined visual fields in patients with hemianopsia.

PURPOSE: To investigate the concordance between subjectively and objectively acquired visual fields in patients with subjectively determined hemianopsia. DESIGN: Retrospective observational study. METHODS: Ten patients, six men and four women, ranging in age from 28 to 68 years, were studied. Goldmann or Humphrey perimeters were used to obtain the subjectively determined visual fields for up to 25 degrees of eccentricity, and the VERIS Scientific System (Electro-Diagnostic Imaging, San Francisco, California, USA) was used to record multifocal visual evoked potential [VEPs] (mfVEPs) to obtain the objective visual fields. Each of the 60 black-and-white segments of the checkerboard stimulus was alternated according to a binary m sequence. The first slices of the second-order kernels were extracted and analyzed. RESULTS: In five cases, the visual field loci where the mfVEPs were within normal limits corresponded to the scotomatous areas obtained by conventional perimetry. In these discordant cases, the lesions (e.g., arteriovenous malformation) were located in the occipital lobe. Two of these cases had a complete recovery of the subjective visual field. The lesions of the concordant cases were located outside the occipital lobe (e.g., pituitary adenoma). In these cases, no visual field improvement was seen. The temporal crescent syndrome was ruled out in patients with posterior lesions by computed tomography (CT) or magnetic resonance imaging (MRI) findings. CONCLUSIONS: In some patients with occipital lesions, the subjective and objective visual field results are discordant, and some of them will show a recovery of the visual field deficits.

Adult↗
PubMedDate not supplied

[Visual suppression during eye movements (a brief review on the problem of the mechanisms and their role in visual perception). II. Their role in visual perception].

A role of both geniculate and tecto-thalamic channels in visual suppression has been considered. Some evolutional aspects of visual suppression are discussed. Both a hypothetical scheme of the multilevel structural and functional organization of visual suppression and a neurophysiological basis of the integration of object's elements to whole image are suggested from the author's papers. The functional role of visual suppression has been not limited the visual stability only but has been considered wider as the important stage of the visual perception by which both the proprioceptive sensation of the object's spatial position arise and the preparation of the visual system for the survey and the processing object's pure visual information (brightness, color, form, etc.) go on. The match of both proprioceptive and visual sensations lead in finally to spatial-visual image of the object.

Animals↗
PubMed2005

Spatial attention triggered by eye gaze enhances and speeds up visual processing in upper and lower visual fields beyond early striate visual processing.

OBJECTIVE: The detection of a lateralized visual target is faster when preceded by a face gazing to the location of this stimulus. Here we aimed to clarify the time-course of the visual processing modulated by these reflexive shifts of attention. METHODS: ERPs were measured on 16 subjects performing a speeded location task on a circular checkerboard. The checkerboard target appeared either on the left or right of the upper or lower visual field, and was preceded by a central face orienting its gaze obliquely to one of the four possible corner locations for the target to appear. RESULTS: Congruently cued targets were located faster than incongruently cued targets and were associated with larger and earlier occipital P1 (approximately 110 ms) and occipito-parieto-temporal N1 (approximately 150 ms) components. However, no such attentional modulations were found on the earlier C1 visual component, best observed with a negative polarity for upper visual field stimulations, and thought to originate largely from primary visual cortex. CONCLUSIONS AND SIGNIFICANCE: These results show that reflexive shifts of attention following oblique eye gaze to upper and lower visual fields increase and speed up the processing of visual information beyond the feedforward flow of information in primary visual cortex.

Adult↗
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↗
PubMed2006

Structure-function relationships in the human visual system using DTI, fMRI and visual field testing: pre- and post-operative assessments in patients with anterior visual pathway compression.

The focus of this project is to improve our understanding of the relationships between brain structure and function in patients presenting with anterior visual pathway compression using functional MRI (fMRI), visual field(VF) maps and diffusion tensor imaging (DTI). Significant visual loss can occur when large pituitary lesions compress the optic chiasm. Surgical resection of these lesions decompresses the chiasm and can lead to visual recovery. In this preliminary study, we selected patients presenting with slowly progressive visual loss secondary to a compressive pituitary region mass. Using preoperative DTI data, we reconstructed white matter projections of the optic radiations and demonstrated a structural correlation with functional vision as quantified by formal visual field mapping and fMRI. The structural data generated through a fiber tracking algorithm may represent a potentially powerful tool to better understand functional visual deficits in patients with anterior visual pathway compression. Furthermore, we believe that specific patterns in preoperative DTI data may predict the likelihood of postoperative visual recovery in a select group of patients.

Brain↗
PubMed2003

Visual field representations and locations of visual areas V1/2/3 in human visual cortex.

The position, surface area and visual field representation of human visual areas V1, V2 and V3 were measured using fMRI in 7 subjects (14 hemispheres). Cortical visual field maps of the central 12 deg were measured using rotating wedge and expanding ring stimuli. The boundaries between areas were identified using an automated procedure to fit an atlas of the expected visual field map to the data. All position and surface area measurements were made along the boundary between white matter and gray matter. The representation of the central 2 deg of visual field in areas V1, V2, V3 and hV4 spans about 2100 mm2 and is centered on the lateral-ventral aspect of the occipital lobes at Talairach coordinates -29, -78, -11 and 25, -80, -9. The mean area between the 2-deg and 12-deg eccentricities for the primary visual areas was: V1: 1470 mm2; V2: 1115 mm2; and V3: 819 mm2. The sizes of areas V1, V2 and V3 varied by about a factor of 2.5 across individuals; the sizes of V1 and V2 are significantly correlated within individuals, but there is a very low correlation between V1 and V3. These in vivo measurements of normal human retinotopic visual areas can be used as a reference for comparison to unusual cases involving developmental plasticity, recovery from injury, identifying homology with animal models, or analyzing the computational resources available within the visual pathways.

Brain Mapping↗
PubMed2005

Lateralized visual behavior in bottlenose dolphins (Tursiops truncatus) performing audio-visual tasks: the right visual field advantage.

Analyzing cerebral asymmetries in various species helps in understanding brain organization. The left and right sides of the brain (lateralization) are involved in different cognitive and sensory functions. This study focuses on dolphin visual lateralization as expressed by spontaneous eye preference when performing a complex cognitive task; we examine lateralization when processing different visual stimuli displayed on an underwater touch-screen (two-dimensional figures, three-dimensional figures and dolphin/human video sequences). Three female bottlenose dolphins (Tursiops truncatus) were submitted to a 2-, 3- or 4-, choice visual/auditory discrimination problem, without any food reward: the subjects had to correctly match visual and acoustic stimuli together. In order to visualize and to touch the underwater target, the dolphins had to come close to the touch-screen and to position themselves using monocular vision (left or right eye) and/or binocular naso-ventral vision. The results showed an ability to associate simple visual forms and auditory information using an underwater touch-screen. Moreover, the subjects showed a spontaneous tendency to use monocular vision. Contrary to previous findings, our results did not clearly demonstrate right eye preference in spontaneous choice. However, the individuals' scores of correct answers were correlated with right eye vision, demonstrating the advantage of this visual field in visual information processing and suggesting a left hemispheric dominance. We also demonstrated that the nature of the presented visual stimulus does not seem to have any influence on the animals' monocular vision choice.

Acoustic Stimulation↗
PubMed1995

Correlating preferential looking visual acuity and visual behavior in severely visually handicapped children.

We developed a series of questions that reflects the functional abilities of severely visually handicapped children. The study population comprised 100 patients aged 30 to 60 months (mean 43.23), mostly afflicted with retinopathy of prematurity. Visual acuity was measured by preferential looking. Preferential looking acuities of the patients ranged from 20/25 (0.8) to 20/6400 (0.003) (mean 20/470 (0.04)). Ten activities were analyzed and correlated with preferential looking acuity. Among the selected visual activities, when children are not interested in television (p = 0.0001), toys (other than those that make sounds (p = 0.0001), and people (p = 0.001)), their preferential looking acuities were very low. For example, 73 out of 100 patients who were visually interested in television had preferential looking acuities (mean 20/245 (0.082)) that were significantly higher (p = 0.001) than 21 patients not interested in television (mean 20/2806 (0.007)). Patients with nystagmus (n = 79) had significantly lower preferential looking acuities (p = 0.0001) (mean 20/1114 (0.018)) than patients with no nystagmus (mean 20/57 (0.35)). When evaluating visual function in young, severely visually impaired patients, in addition to preferential looking testing, analyzing visual behavior within the environment is important to accurately evaluate their remaining visual abilities.

Child, Preschool↗
PubMed2006

Functional activation in parieto-premotor and visual areas dependent on congruency between hand movement and visual stimuli during motor-visual priming.

Electrophysiological studies in monkeys and neuroimaging studies of humans have shown that action execution and action observation share neural processing sites traditionally thought to be responsible for motor execution alone. This experiment investigates a behavioral phenomenon in which a visual discrimination task is influenced by concurrent motor performance. Functional magnetic resonance imaging (fMRI) was used to determine whether this discrimination task uses components of the motor system. Participants viewed and responded to an animated hand while performing either congruent or incongruent right hand actions; the visual presentation was either a sequence showing a hand opening and closing, or randomly ordered frames from this series. The participant responded to onscreen target hand postures on a left footpedal. Previous behavioral results have shown a reaction time advantage on this discrimination task when performing congruent compared to incongruent hand actions, but only for sequential visual presentation. Left superior parietal lobule (SPL) and dorsal premotor cortex were more strongly activated when visual series and hand action did not match, as were dorsal premotor cortex and primary visual cortex. These results suggest that mismatches between performed action and visual feedback produce an inaccurate neural representation of limb state, which we suggest causes the contralateral SPL activation. This representation could not be used in the visual discrimination task, requiring increased reliance on direct visual inputs in order to perform the discrimination task accurately.

Adolescent↗