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PubMed1999

Reduced visual evoked responses in multiple sclerosis patients with optic neuritis: comparison of functional magnetic resonance imaging and visual evoked potentials.

The limited application of functional magnetic resonance imaging (fMRI) for investigations of multiple sclerosis (MS) patients has already shown that deficits of the motor, cognitive and visual systems may be identified by differences in the patterns of activation in response to a suitable stimulus. In MS patients with unilateral optic neuritis, the area of activation in the primary visual cortex, measured by fMRI techniques, is dramatically reduced in response to stimulation of the affected eye. The latency of the major positive component of the visual evoked potential (VEP) recorded upon stimulation of the affected eye is significantly increased in these patients, as compared to the unaffected eye and normal volunteers. We have found a correlation between the neural response measured using fMRI and the latency of the VEP. fMRI signal responses have the potential to provide more detailed topographic information relating to functional deficits in MS.

Evoked Potentials, Visual↗

PubMed2005

The developmental test of visual perception-2 normative study on the visual-perceptual function for children in Hong Kong.

This research study intended to investigate the visualperceptual performance of children in Hong Kong by comparing them to the accepted norms on the Developmental Test of Visual Perception-2nd edition. The research examined whether there was significant difference in child's gender, age, and grade. The normative study recruited two hundred and eight-nine children between the ages of 6 and 7 in normal primary schools in Hong Kong. Results indicated that there was a ceiling effect in eye-hand coordination, position in space and spatial relations subtests. Grade differences were found to be significant in all subtests except eye-hand coordination and visual-motor speed. On the other hand, there were no statistical difference in the test scores between boys and girls except on copying and figure-ground subtests. It is concluded that there is a strong need to ensure that norms for visual-perceptual tests are appropriate for the specific cultural groups being assessed.

Child↗

PubMed2005

Visual selection and posterior parietal cortex: effects of repetitive transcranial magnetic stimulation on partial report analyzed by Bundesen's theory of visual attention.

Posterior parietal cortex (PPC) may contribute to visual selection by exerting top-down influences on visual processing. To seek direct evidence for this, we used 10 Hz repetitive transcranial magnetic stimulation (rTMS) over right or left PPC in nine healthy volunteers during a partial (selective) report task that allows quantitative assessment of top-down control and other parameters. Participants reported digits in a relevant color ("targets") but not those in an irrelevant color ("nontargets") from a brief masked display, in which a target could appear alone or together with an accompanying item (nontarget or target) in the same or opposite hemifield. Generally, a given target is identified better when presented with a nontarget than with another target, indicating top-down selection of task-relevant targets; this applied here with no rTMS or left PPC rTMS. However, rTMS over the right PPC changed the performance pattern. A left target no longer impeded report of a right target more strongly than did a left nontarget, whereas the greater impact of a right target than a right nontarget in disrupting report of a left target was increased. Formal analysis in terms of Bundesen's (1990) theory of visual attention indicated that right PPC rTMS diminished top-down control for the left hemifield while enhancing this for the right hemifield, particularly for bilateral two-item displays. These findings indicate a role for right PPC in top-down spatial selection, which applies even when the target is defined by a nonspatial property (here color).

Adult↗

PubMed2000

Isoluminant monochromatic and polychromatic visual backgrounds alter response characteristics of cat visual neurons after stimulation with stationary and moving light bars.

The role of colour vision in night-active cats has not been elucidated completely hitherto. In order to assess the colour sensitivity in cat cortical neurons we used large isoluminant computer-generated monochromatic and polychromatic background stimuli which were superimposed on moving and stationary (on/off) light bars. Background stimuli were moved at different speeds either inphase or antiphase. The modulatory effect of the visual noise on the neuronal bar was the primary objective of the study. The maximum PSTH peaks of some 40% of the neurons tested was influenced by both moving and stationary bars. About 2 thirds of maximum peak-sensitive cells showed also altered direction selectivity. Latencies and field widths, on the other hand, turned out to be rather stable. The retino-cortical conduction time was not influenced either. In conclusion, a large portion of cat cortical visual neurons is remarkably sensitive to the spectral composition of the visual noise process surrounding the stimulating light bar.

Animals↗

PubMed2006

Visual function with acupuncture tested by visual evoked potential.

Visual evoked potential (VEP) testing is used frequently and is an important ophthalmologic physiological test to examine visual functions objectively. The VEP is a complicated waveform consisting of negative waveform named N75 and N135, and positive waveform named P100. Delayed P100 latency and greatly attenuated amplitude on VEP are known characteristics for diagnosing optic nerve disease. Acupuncture has been used to treat wide clinical symptoms with minimal side effects. The confirmation of the efficacy of acupuncture generally relies on subjective symptoms. There is not much scientific evidence supporting the acupuncture treatments for eye diseases up to today. However, the VEP test can evaluate objectively and numerically the efficacy of the treatment by the acupuncture. We analyzed 19 healthy subjects (38 eyes). The P100 latencies in the group of less than 101.7 msec (total average) before acupuncture stimulations were not different than those after treatment (98.2 +/- 3.0 msec, 98.2 +/- 4.0 msec, respectively, p = 0.88, n = 17), but the latencies in those subjects with longer or equal to 101.7 msec were statistically different after acupuncture (104.6 +/- 2.8 msec, 101.9 +/- 3.7 msec, respectively, p = 0.006, n = 21). These results show that the acupuncture stimulation contributes to the P100 latencies of pattern reversal (PR)-VEP to some subjects who have delayed latencies, and this electrophysiological method is a valuable technique in monitoring the effectiveness of acupuncture therapy in the improvements of visual functions. The purpose of this study is to evaluate the physiological effects by acupuncture stimulations using PR-VEP in normal subjects.

Acupuncture Therapy↗

PubMed1998

Visual and kinesthetic control of goal-directed movements to visually and kinesthetically presented targets.

The study investigated the contribution of kinesthetic and visual input to the performance of reaching movements and identified rules governing the transformation of information between these two sensory modalities. The study examined the accuracy by which 39 subjects reproduced locations of five targets in a horizontal plane. Mode of target presentation and feedback during reproduction of a target's location was either visual, kinesthetic or a combination of both modalities. Thus, it was possible to examine performance when target presentation and reproduction involved feedback from the same sensory modality (intramodal) as well as from different sensory modalities (intermodal). Errors in target reproduction were calculated in terms of distance and systematic biases in movement extent. The major findings of the study are (1) Intramodal reproduction of a target's location on the basis of kinesthetic feedback is somewhat less accurate than intramodal reproduction on the basis of visual feedback (2) Intermodal performance is significantly less accurate than intramodal performance. (3) Accuracy of performance does not depend on the direction of information transfer between sensory modalities. (4) Intermodal performance is characterized by systematic biases in extent of movement which are dependent on the direction of information transfer between modalities. (5) When presentation of the target's location is bimodal, reproduction is adversely affected by the conflicting input. The results suggest that transformation rules, used to combine input from various sensory modalities, depend on environmental conditions and attention.

Adult↗

PubMed2001

Spontaneous blinks as a criterion of visual fatigue during prolonged work on visual display terminals.

Visual fatigue caused by prolonged work viewing a Visual Display Terminals (VDT) and of work reading a hard-copy were assessed by electromyogram (EMG) waveform and electrooculogram (EOG) waveform in spontaneous blinks as objective criteria, and by questionnaire of subjective feeling, and by task performance. The duration and the amplitude of the EMG of the orbicularis ocular muscle on the right side and the EOG of the vertical direction to the eyelid were measured for 10 subjects who participated in a figure task consisting of the addition of single-digit numbers on a VDT work or a work with a hard-copy. The mean values of the duration and the amplitude of the EMG and the EOG were evaluated by the averaging of 10 waveforms of the spontaneous blinks for all subjects. The time lag from the EMG to the EOG in the process of the generation of spontaneous blinks was also analyzed. These five parameters were evaluated during the work time. The mean values for the duration of the EMG increased gradually during the work time, but the amplitude did not show significant difference between the prework and a work time. There was no significant change of the duration of the EOG, but the mean amplitude of the EOG decreased as the work time progressed, and the time lag significantly extended. The blinks frequency increased relatively when using a VDT. The rate of fluctuation for these parameters was higher during use of a VDT than use of a hard-copy. The time lag at five hours of VDT work was extended by 90% based on the value at the pre-work. The symptoms of general fatigue and fatigue of the eyes increased linearly during the VDT work for six hours. The results indicated a significant correlation between the objective parameters for the activity of the spontaneous blinks, i.e., duration and amplitude of EMG and EOG, and the time lag between EMG and EOG, and the subjective feeling was recognized in the time course of the task. These experimental results suggested that the parameters regarding the EMG and the EOG for the spontaneous blinks were effective indices for assessing visual fatigue during prolonged VDT work.

Adult↗

PubMed1990

The effect of visual angle on global and local reaction times depends on the set of visual angles presented.

It has been shown that there is a transition from a global to a local advantage in reaction time as visual angle increases (Kinchla & Wolfe, 1979), and it has been assumed that this transition reflects lower level (e.g., retinal) processes. In three experiments, we examined whether higher level (e.g., attentional) processes play a role in this transition. In each experiment, subjects received a different stimulus set in each of two blocks of trials. In Experiment 1, stimuli subtending 1.5 degrees, 3 degrees, 4.5 degrees, or 6 degrees of visual angle vertically (small-stimuli set) were randomly presented in one block, while the other block consisted of random presentations of 3 degrees, 6 degrees, 9 degrees, or 12 degrees stimuli (large-stimuli set). The subjects' task was to identify targets that appeared randomly at either the local or the global level. It was found that the transition from a global to a local reaction-time advantage took place at a larger visual angle for the large-stimuli set than for the small-stimuli set. The same effects of stimulus set were found in Experiment 2, in which the small-stimuli set included 1.5 degrees, 3 degrees, or 6 degrees stimuli while the large-stimuli set included 3 degrees, 6 degrees, or 9 degrees stimuli. In Experiment 3, eye position was monitored to rule out the possibility that subjects adopted different fixation strategies depending on which stimulus set was being presented. The findings suggest that attention plays a major role in determining the relative speed of processing of local-and global-level information.

Aged↗

PubMed1996

[The estimation of the curvature of visual space with a visual triangle].

Triangular properties which Blank (1961) proposed are useful in investigating the geometry of visual space. With this method, however, it is not possible to estimate quantitatively the curvature of visual space. In the present article, hyperbolic and elliptic triangles are described with mathematical equations in the two and three dimensional Euclidean maps, and a method is proposed to estimate the curvature with triangular properties. Further, one experiment is conducted to find how the curvature changes according to the experimental conditions. Visual triangles are constructed in an eye level plane, a slanted plane and a horopter plane. The result shows that the curvature is negative in the eye level plane and in the slanted plane, but positive in the horopter plane.

Humans↗

PubMedDate not supplied

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

A problem of visual suppression during eye movements is discussed. The short critical review of the main published papers is adduced. A comparative analysis of the literary and author's data has been considered. These data provide evidence for the existence of three but not two (how is maintained) mechanisms of visual suppression: a retinal, efferent copy, and proprioceptive (from extraocular muscles) signals. The proprioceptive mechanism is more powerful than efferent copy. Both retinal and extraretinal mechanisms of visual suppression are discussed in detail. The sources and the passage's pathways of the extraretinal signals are considered thoroughly. It is shown that the retino-geniculate system provide mainly retinal mechanisms vs the tecto-thalamic system provide extraretinal mechanisms.

Animals↗

PubMed1992

Lesions of the perirhinal cortex but not of the frontal, medial prefrontal, visual, or insular cortex block fear-potentiated startle using a visual conditioned stimulus.

The present study is part of an ongoing series of experiments aimed at delineation of the neural pathways that mediate fear-potentiated startle, a model of conditioned fear in which the acoustic startle reflex is enhanced when elicited in the presence of a light previously paired with shock. A number of cortical areas that might be involved in relaying information about the visual conditioned stimulus (the light) in fear-potentiated startle were investigated. One hundred thirty-five rats were given 10 light-shock pairings on each of 2 consecutive days, and 1-2 d later electrolytic or aspiration lesions in various cortical areas were performed. One week later, the magnitude of fear-potentiated startle was measured. Complete removal of the visual cortex, medial prefrontal cortex, insular cortex, or posterior perirhinal cortex had no significant effect on the magnitude of fear-potentiated startle. Lesions of the frontal cortex attenuated fear-potentiated startle by approximately 50%. However, lesions of the anterior perirhinal cortex completely eliminated fear-potentiated startle. The effective lesions included parts of the cortex both dorsal and ventral to the rhinal sulcus and extended from approximately 1.8 to 3.8 mm posterior to bregma. Lesions slightly more posterior (2.3-4.8 mm posterior to bregma) or lesions that included only the perirhinal cortex dorsal to the rhinal sulcus had no effect. The region of the perirhinal cortex in which lesions blocked fear-potentiated startle projects to the amygdala, and thus may be part of the pathway that relays the visual conditioned stimulus information to the amygdala, a structure that is also critical for fear-potentiated startle. In addition, the present findings are in agreement with numerous studies in primates suggesting that the perirhinal cortex may play a more general role in memory.

Acoustic Stimulation↗

PubMedDate not supplied

Time information in Poggendorff visual illusion: visual evoked potentials.

Using the component sets of the Poggendorff visual illusion as optical stimuli (comprising two horizontal and parallel segments intersected by two oblique segments), we recorded the respective visual evoked potentials (VEPs). Depending on the different delta t passing between the constitutive elements of the Poggendorff illusion, it was found that there was a greater latency of VEP components for the visual stimulus presentation sequence in which oblique segments are projected before horizontal segments.

Adult↗

PubMed2003

Relative role of visual and non-visual cues in determining the direction of "up": experiments in the York tilted room facility.

Perceiving a direction as "up" is fundamental to human performance and perception. Astronauts in microgravity frequently experience reorientation illusions in which they, or their world, appear to flip and 'up' becomes arbitrarily redefined. This paper assesses the relative importance of visual cues in determining the perceived up direction. In the absence of information about the origin of illumination, people interpret surface structure by assuming that the direction of illumination is from above. Here we exploit this phenomenon to measure the influence of head and body orientation, gravity and visual cues on the perceived up direction. Fifteen subjects judged the shape of shaded circles presented in various orientations. The circles were shaded in such a way that when the shading was compatible with light coming from above, the circle appeared as a convex hemisphere. Therefore, by finding which shaded circle appeared most convex, we can deduce the direction regarded as "up". The different cues contributing to this percept were separated by varying both the orientation of the subject and the surrounding room relative to gravity. The relative significance of each cue may be of use in spacecraft interior design to help reduce the incidence of visual reorientation illusions.

Adult↗

PubMed2004

[Visual perception of Kanji characters and complicated figures. Part 3. Visual P300 event-related potentials in patients with attention deficit/hyperactivity disorders].

In order to evaluate visual perception, the P300 event-related potentials (ERPs) for visual oddball tasks were recorded in 11 patients with attention deficit/hyperactivity disorders (AD/HD), 12 with mental retardation (MR) and 14 age-matched healthy controls. With the aim of revealing trial-to-trial variabilities which are neglected by investigating averaged ERPs, single sweep P300s (ss-P300s) were assessed in addition to averaged P300. There were no significant differences of averaged P300 latency and amplitude between controls and AD/HD patients. AD/HD patients showed an increased variability in the amplitude of ss-P300s, while MR patient showed an increased variability in latency. These findings suggest that in AD/HD patients general attention is impaired to a larger extent than selective attention and visual perception.

Attention↗

PubMed1986

The effect of protective sports eyewear on peripheral visual field and a peripheral visual performance task.

Seven different types of protective sports eyewear were tested to determine whether peripheral awareness as measured with a visual performance task were affected. Goldmann perimetry and the Wayne Saccadic Fixator with Stik-Up attachments were utilized in a repeated measures research design. The sports glasses did restrict visual field, but no one pair of glasses were least restrictive. The restrictions did not translate into significant differences on the performance task. Peripheral visual factors should be taken into account when prescribing protective sports eyewear. The importance of proper eye protection in sports is also discussed.

Adult↗

PubMed1985

[Value of visual evoked potentials (VEP) in compression of the anterior visual pathway, especially in the area of the chiasm].

We investigated 86 patients by pattern half-field stimulation presenting clinically with temporal field-defects or with a mass causing compression of the visual pathways found by C.T.-scanning. Pattern half-field stimulation proved to be a very sensitive method for detecting a compression of the anterior visual pathways. In 65 cases the results of perimetry and VEP were congruent, 6 times the evoked potential was pathologic the perimetry showing no abnormalities, only 1 false negative VEP was observed. Thus we stress the importance of an investigation by VEP including half-field stimulation in all patients with suspected compression of the anterior visual pathways.

Evoked Potentials, Visual↗

PubMed1979

[Induced visual hallucinations and visual adaptation disorders in patients with delirium tremens].

In 91 cases of alcoholic delirium, acute alcoholic hallucinosis and alcoholic withdrawal conditions, a clinico-experimental study of the formation of evoked visual hallucinations was conducted with the aid of a dozed compression of the eye (a modification of Lippman's test). The following 3 stages in the development of pseudoperception are described: sensorial, hallucinoid, hallucinatory. A parallel study of visual dark adaptation (40 cases) and brain bioelectrical activity (37 patients) detected 7 pathological types of changed time of visual dark adaptation and disorders of brain bioelectrical activity. These factors are connected with conditions of sensorial disadaptation, having a clinico-diagnostic significance.

Acute Disease↗

PubMed1979

Rapid assessment of visual function: an electronic sweep technique for the pattern visual evoked potential.

We have developed an electronic spatial frequency sweep technique for electrophysiological assessment of visual acuity and pattern vision. The technique allows an accurate and reliable measurement of VEPs to a full range of spatial frequencies in just 10 sec. Because the measurements are so rapid, the technique suggests several new improvements in the assessment of visual function. Sweeping spatial frequency linearly and extrapolating the high-frequency region of the VEP spatial-tuning function to zero voltage allows an estimate of acuity which correlates highly with psychophysical estimates of acuity. Variants of the procedure are appropriate for the assessment of refracture error, determination of equality of visual function for the two eyes and of binocular interactions, and for sequential assessment of therapeutic conditions.

Amblyopia↗