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At least 1,657 records · Page 92Linked to original sources
PubMed1989

[Pattern electroretinography and pattern visual evoked potentials in maculopathy: a comparison with sensory tests].

The retinal and cortical potentials for pattern reversal were recorded in 58 eyes of 30 patients afflicted with macular disease. The highest incidence of abnormality (79%) was found for the amplitudes P-ERG and P-VECP. Total field EOG and L-ERG were affected less frequently (41% and 25%). The P-ERG amplitude correlated significantly with the sensitivity of the central 10 degrees visual field (static perimetry). The P-VECP threshold check size showed a close correlation with visual acuity. Thus, the recording of pattern-evoked retinal and cortical potentials serves as a supplementary means of assessing types of maculopathy.

Adolescent↗
PubMed1993

Electroretinogram and visual evoked potential in two siblings with adult form galactosialidosis.

We recorded flash electroretinograms (ERGs), flash visual evoked potentials (VEPs), pattern ERGs and pattern VEPs in two siblings with adult form galactosialidosis. The amplitude of b-wave was decreased in flash ERGs. The peak latency of flash VEPs was within normal range. The pattern ERGs and VEPs were nonrecordable. These results suggested the damage of retinal ganglion cell and inner nuclear layer in these cases.

Adult↗
PubMed1996

[Objective determination of visual acuity. Improvement of an infrared nystagmography method and comparison with pattern visual evoked potentials].

BACKGROUND: The purpose of this study was to optimize a new nystagmographical method of objective assessment of visual acuity and compare it to an electrophysiological method. METHODS: In the nystagmographical method motionless brake marks were superimposed on a moving grating pattern, causing suppression of optokinetic nystagmus (OKN). The smallest brake mark that interrupted the OKN was taken as an objective measure for visual acuity (VA). In the electrophysiological method rapid sequences of high-contrast checkerboard patterns of different spatial frequency were presented in a pattern on-off mode in a foveal field. The VEP response function was extrapolated to 0 microV. The objective values of 94 healthy eyes with artificially reduced vision (VA 0.05-2.0) and 314 eyes with pathological reduction of VA due to different etiologies were compared. RESULTS. The selectivity of the nystagmographical method could be improved. With the exception of strabismic amblyopia, the results were closely correlated with the VA. The least VA could be estimated in steps of 0.06, 0.1, 0.2, 0.5 and 0.8. CONCLUSIONS: The new nystagmographical method yields useful information about the least VA if strabismic amblyopia is excluded.

Adolescent↗
PubMed1997

Decreased contrast sensitivity in normal tension glaucoma determined by pattern visually evoked cortical potentials.

Little is known about the central visual function of patients with normal tension glaucoma (NTG). We estimated the contrast sensitivity of patients with NTG and normal subjects with the use of pattern visually evoked cortical potentials (PVECPs). PVECPs were recorded using checkerboard pattern reversal system display on television monitor of check size 15', 60' and frequency 3 reversals per second and contrast varied in 7 steps. Our results show that a significant delay of the P100 component for 60' check size in the NTG group was found at every contrast level (P < 0.05). Contrast threshold was determined as the value to obtain a criterion peak latency from a regression line calculated within a contrast range from 10% to 56%. The contrast threshold for both check sizes of the NTG group showed an increased threshold (P < 0.05). We conclude that contrast sensitivity decreased in NTG as determined by PVECP. The PVECP was a sensitive test for detecting the functional abnormalities of NTG.

Contrast Sensitivity↗
PubMed1998

Multifocal topographic visual evoked potential: improving objective detection of local visual field defects.

PURPOSE: To investigate the relationships between the pattern stimulation of different parts of the visual field (up to 25 degrees of eccentricity), the electrode position, and the cortical response to improve objective detection of local visual field defects. METHODS: The human visual evoked potential (VEP) was assessed using multifocal pseudorandomly alternated pattern stimuli that were cortically scaled in size. Monopolar and bipolar electrode positions were used. The visual field was investigated up to 26 degrees of eccentricity. Twelve normal subjects and seven subjects with visual field defects of different nature were studied. RESULTS: Although the monopolar response is heavily biased toward the lower hemifield, bipolar leads overlying the active occipital cortex (straddling the inion) demonstrate good signals from all areas of the visual field tested. The amplitude is almost equal for the averaged upper and lower hemifields, but the polarity is opposite, causing partial cancellation of the full-field VEP. The degree of cancellation depends mainly on latency differences between the vertical hemifields. The bipolar VEP corresponded well with Humphrey visual field defects, and it showed a loss of signal in the scotoma area. CONCLUSIONS: The multifocal VEP demonstrates good correspondence with the topography of the visual field. Recording with occipital bipolar electrode placement is superior to standard monopolar recording. To avoid a full-field cancellation effect, a separate evaluation of upper and lower hemifields should be used for the best assessment of retinocortical pathways. This technique represents a significant step toward the possible application of the multifocal VEP to objective detection of local defects in the visual field.

Adult↗
PubMed2000

Novel vs. well-learned memory for faces: a positron emission tomography study.

Previous work has suggested that familiarity/novelty of learned materials affects the circuitry involved in memory, primarily in the size of activations rather than the pattern of activation. Although this work has examined both recall and recognition, it has been limited to verbal material. In this study, we set out to determine if the same result applies to nonverbal memory. We used the same experimental design, but used faces as the memory task. Healthy volunteers thoroughly learned a set of 18 faces a week prior to the Positron Emission Tomography (PET) experiment (well-learned memory) and were asked to remember another set of 18 faces, to which they were exposed 1 min before the PET experiment (novel memory). During the PET session, their task was to recognize the faces learned a week before and the faces seen a minute before; the "remembered faces" were interspersed among entirely new (distractor) faces. We found that, unlike for verbal material, the retention interval and the familiarity level of the faces affected both the pattern and the size of activations. Comparing the novel and well-learned recognition tasks revealed that novel memory for faces is primarily a frontal-lobe task, while well-learned recognition memory for faces utilizes a more distributed neural circuit, including visual areas, which appear to serve as memory-storage sites.

Adult↗
PubMed2004

Sex differences in functional activation patterns revealed by increased emotion processing demands.

Two [O(15)] PET studies assessed sex differences regional brain activation in the recognition of emotional stimuli. Study I revealed that the recognition of emotion in visual faces resulted in bilateral frontal activation in women, and unilateral right-sided activation in men. In study II, the complexity of the emotional face task was increased through tje addition of associated auditory emotional stimuli. Men again showed unilateral frontal activation, in this case to the left; whereas women did not show bilateral frontal activation, but showed greater limbic activity. These results suggest that when processing broader cross-modal emotional stimuli, men engage more in associative cognitive strategies while women draw more on primary emotional references.

Adult↗
PubMed1998

Similarity-based models of human visual recognition.

Seven models of human visual recognition from cognitive psychology, visual psychophysics and connectionism were compared. They were used to predict psychophysical classification data obtained via supervised learning with parametrised grey-level patterns (compound Gabor signals). Four sets of learning patterns, as well as foveal and extrafoveal viewing conditions, were applied. Model performance was determined by comparing observed and predicted data with respect to root mean square deviation and to signal reconstruction via multidimensional scaling. Results show that a psychophysical theory of classification requires a similarity concept that is based both on physical signal description and on cognitive bias. The latter is less pronounced in foveal recognition, where all seven models performed almost equally well, but matters in extrafoveal recognition. Virtual prototype models (Rentschler et al. (1994), Vision Research 34, 669-687), which best accommodate stimulus- and observer-dependencies, are then of advantage. Concerning computational efficiency, a hyperBF model (Poggio and Girosi (1990), Science 247, 978) was much faster, and generalized signal detection models were much slower than the average.

Cognition↗
PubMed1997

Object recognition difficulty in visual apperceptive agnosia.

Two patients with visual apperceptive agnosia were examined on tasks assessing the appreciation of visual material. Elementary visual functioning was relatively preserved, but they had profound difficulty recognizing and naming line drawings. More detailed evaluation revealed accurate recognition of regular geometric shapes and colors, but performance deteriorated when the shapes were made more complex visually, when multiple-choice arrays contained larger numbers of simple targets and foils, and when a mental manipulation such as a rotation was required. The recognition of letters and words was similarly compromised. Naming, recognition, and anomaly judgments of colored pictures and real objects were more accurate than similar decisions involving black-and-white line drawings. Visual imagery for shapes, letters, and objects appeared to be more accurate than visual perception of the same materials. We hypothesize that object recognition difficulty in visual apperceptive agnosia is due to two related factors: the impaired appreciation of the visual perceptual features that constitute objects, and a limitation in the cognitive resources that are available for processing demanding material within the visual modality.

Aged↗