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Results for “Pattern Recognition, Visual”

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At least 523 records · Page 29Linked to original sources
PubMed1986

Assessment of vision in amblyopia.

This paper presents a brief review of clinical methods of assessment of vision in amblyopic infants and children. The problems encountered in this context include attention and motivation of the patient, and reliability and standardisation of method. Various solutions are examined and the relevance of the newer techniques of acuity estimation by preferential looking (PL), visual evoked cortical potentials (VECP) and psychophysical tests of contrast sensitivity is discussed.

Amblyopia↗
PubMed1987

Serial recording of VEPs to different stimuli in multiple sclerosis patients.

VEPs to different spatial frequencies (1,2,4 cycles per degree) and different stimulus configurations (vertical, horizontal gratings and checkerboard) were recorded in 47 Multiple Sclerosis patients and a corresponding group of control subjects. Serial recordings were performed in periods of 1-6 years. We show that the highest diagnostic yield in MS is for VEPs of higher spatial frequency than 1 cpd, and that vertical gratings give reliable results when high spatial frequencies are used, whereas checkerboard stimuli elicit consistent VEPs only when the check size is 30'-15' of arc of visual angle. The use of fine vertical grating patterns dissipates controversies dependent on "W" shaped VEPs.

Adult↗
PubMed1985

The VER as a predictor of normal visual acuity in the adult human eye.

The ability of the evoked potential to predict conventional visual acuity, as measured with a Landolt C test, was investigated for subjects with normal acuities. Both peak-to-trough and Fourier-analysed amplitudes were used. The extrapolation technique assumed curvilinear regression and produced correlations no better than did a method employing amplitude measurements of a single check size of 5.5 min arc (r = 0.67). Assessment of Landolt C acuity by subjective use of the evoked potential stimulus was unable to produce a higher correlation.

Adolescent↗
PubMed1983

[Pattern reversal VEP in TV and moving-mirror stimulation: a methodological comparison].

Pattern-Reversal visual evoked potentials (VEP) were elicited in 10 controls by optomechanical and TV-reversal. TV-stimulation was done in the frame-locked and -unlocked mode. Comparing P2-latencies evoked by different stimulation fields of the screen delays up to 30 ms and increased standard deviations could be observed in the TV-stimulation modes. Moreover, stimulating with small checks a diminution of amplitudes and a simplification of the shape was seen in contrary to the mirror method.

Evoked Potentials, Visual↗
PubMed1983

An early peak of the pattern reversal evoked potential (PREP).

An early peak of the pattern reversal evoked potential with an implicit time between 30 and 50 msec, and an amplitude of 0.5-1 muv was demonstrated. The peak varies with the spatial frequency of the stimulus (checksize), and, the viewing condition (binocular vs monocular). Further study is being done to determine the origin.

Evoked Potentials, Visual↗
PubMed1983

The effect of selective attention on pattern-specific visual evoked potentials.

In a complex choice reaction time experiment, patterned stimuli without luminance change were presented, and pattern-specific visual evoked potentials to lower half-field stimulation were recorded. Two experimental conditions were used. The first was the between-field selection, where square patterns were presented in either the lower or the upper half of the visual field. In a given stimulus run one of the half-fields was task-relevant, and the subjects' task was to press a microswitch to stimuli of higher duration value (GO stimuli), while they had to ignore shorter ones, i. e. stimuli of lower apparent spatial contrast (NOGO stimuli). They had to ignore the stimuli appearing in the irrelevant half-field (IRR stimuli). In order to ensure proper fixation, the subjects had to press another microswitch at the onset of a dim light at the fixation point (CRT stimuli). Our second experimental condition was the within-field selection, where the GO, NOGO, and IRR stimuli appeared in the lower half of the visual field. GO and NOGO were square patterns while IRR stimuli were constructed of circles, or vice versa. (The CRT stimuli were the same as in the previous condition.) Three pattern-specific visual evoked potential components were identified, i. e. CI (70 ms latency), CII (100 ms latency), and CIII (170 ms latency). There were marked selective attention effects on both the CI-CII and CII-CIII peak-to-peak amplitudes. In both experimental conditions, responses with the highest amplitude were evoked by the GO type of stimuli, while the IRR stimuli evoked the smallest responses. According to these results, attention effects on the pattern-specific visual evoked potentials in the first 200 ms cannot be attributed to a simple stimulus set kind of selection.

Adolescent↗