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J B Siegfried

Publications and source records attributed to J B Siegfried.

10 recordsLinked to original sources
PubMed1983

Origin of wavelets in the visual evoked potential.

Low amplitude high frequency wavelets have been demonstrated to be ubiquitous in the visual system of animals and are observed in the ERG of man. Wavelets have also been observed superimposed upon large slow waves obtained from electrodes on occipital scalp. Presently, the rather stereotypic wavelet repetition rate permitted the use of active analog filters tuned to 100 Hz, with a 60-200 Hz bandpass which produced no measurable distortion at 100 Hz. With this method we recorded a series of wavelets in 15 of 16 subjects that usually began from 35 to 40 msec following the onset of a 10(4) troland, 25 degrees visual angle 100 msec flash. We then sought to determine the origin of these wavelets. Wavelets recorded between occiput (Oz) and vertex (Cz) had photopic spectral sensitivity that differed from that of ERG wavelets simultaneously recorded. Moreover, in a topographical study, wavelets recorded between Cz and various lateral positions reached a maximum at Oz; and when adjacent bipolar electrode pairs were used, wavelet polarities inverted as pairs were moved across the occipital region. Thus wavelets recorded between 35 and 70 msec were likely generated from occipital cortex rather than retinal, sub cortical, or diffuse cortical sites. In addition, the topographical distribution of slow wave ('P100') and wavelets differed. Wavelet latencies had a different relation to retinal illuminance than P100 latencies, suggesting that P100 and wavelets have different neurogeneses. Wavelets recorded between Oz and Cz thus reflect the earliest cortical visual processing recorded in man.

Brain↗
PubMed1981

Early wavelets in the VECP.

With the use of a Maxwellian view optical system to present light flashes to the right eye, electroretinograms (ERGs) and visual evoked cortical potentials (VECPs) were recorded from normal subjects. The first 120 msec postflash onset was examined. A series of five VECP wavelets was recorded with implicit times of 50, 72, 82, 90, and 101 msec, at the highest radiance used. Recordings of ERGs in the same experimental session revealed a series of three wavelets with implicit times of 23, 30, and 38 msec. It is concluded that the VECP wavelets are not volume-conducted from the retina and probably represent initial arrival of visual information at the cortex, or subcortical activity.

Electroretinography↗
PubMed1978

Recording monocular VEPs under binocular conditions.

This report describes a technique for recording the visual evoked potential (VEP) arising from 1 eye under conditions of binocular pattern stimulation. The subject views a sinusoidally modulated vectographic checkerboard with orthogonally oriented polarizing filters before the eyes. This technique results in waveforms that contain monocular VEPs distributed in time. The technique is sensitive to interocular suppression and controls for the influence of various extraneous sources of variability. It is useful in clinical VEP testing.

Evoked Potentials↗
PubMedDate not supplied

Abnormal function of the parvocellular visual system in anisometropic amblyopia.

PURPOSE: To study the function of the parvocellular (P) and the magnocellular (M) visual systems with steady-state visual evoked potentials (VEPs) in anisometropic amblyopes. METHODS: A matrix of isolated checks was superimposed on a steady background with different check sizes and temporal frequencies to form specific stimuli to preferentially activate the P or the M visual system. The amplitude of the VEP fundamental frequency was analyzed at the electrode Oz of 5 anisometropic amblyopes and 22 normal subjects. The normal subjects were tested at two visual acuity (VA) levels, 20/20 and 20/40, modified by lenses, to match with the VA levels of the fellow eyes and the amblyopic eyes of the amblyopes, respectively. RESULTS: No significant amplitude difference was found between the dominant eyes and nondominant eyes of the normal subjects for either P or M stimuli at both 20/20 and 20/40 VA levels (P>.05). No significant amplitude difference was found between the fellow eyes of the amblyopes and the dominant eyes of normals for either P or M stimuli at 20/20 VA level (P>.05). A significant amplitude difference was found between the amblyopic eyes and the nondominant eyes of the normals for P stimuli (P<.05) but not for M stimuli (P>.05) at 20/40 VA level. CONCLUSIONS: The amplitude of the VEP fundamental frequency was selectively reduced for P stimuli in anisometropic amblyopic eyes. This clinical electrophysiologic finding confirms that only the function of the P visual system is abnormal in anisometropic amblyopic eyes.

Adolescent↗