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W D Gibbons

Publications and source records attributed to W D Gibbons.

11 recordsLinked to original sources
PubMed1982

Differences among humans in steady-state evoked potentials: evaluation of alpha activity, attentiveness and cognitive awareness of perceptual effectiveness.

We examined some of the variables that were possible sources of the wide variability among and within human subjects in their steady-state visual evoked potentials (VEP) in response to continuously counter-phased visual stimuli (vertical bars). We found that within a given subject the magnitude of VEP was reasonably consistent during replicate trials under comparable conditions. However, across subjects there were enormous differences (as much as 17-fold) in the VEP magnitude (i.e. in the spectral power developed at the stimulus reversal frequency). These differences could not be explained by differences among subjects in arousal (alpha activity before or during stimulation), attentiveness (as indicated by reaction times to random cueing), or by a person's subjective impression of his responsiveness to stimulation.

Adult↗
PubMed1981

Perceptual distortions in visual-evoked potentials.

We tested ten healthy men, ranging in age from 24 to 55 years, to determine whether "drifting" of a fixation target during pattern-stimulus testing was the result of stimulus-induced ocular movements or a purely perceptual response with no oculomotor basis. We also wanted to learn whether this drifting interfered with the development of the visual-evoked potential. We observed large intersubject differences in visual-evoked potential magnitude that could not be explained by either actual or perceived drifting. Perceived drifting did not correlate with actual or perceived drifting. Perceived drifting did not correlate with actual ocular movements. Moreover, when sporadic ocular movements occurred, they did not interfere with the visual-evoked potential; there were no correlations between magnitude of visual-evoked potential and the percentage of time that drifting was perceived.

Adult↗
PubMed1977

Retinal damage from long-term exposure to laser radiation.

The maculae of rhesus monkeys were exposed to an argon-ion lazer operated in the TEM00 continuous wave mode at a wavelength of 514.5 nm. Both ophthalmoscopic and histopathologic evaluations of exposure sites were obtained. Threshold (ED50) values were obtained for 0.5, 5, 30, 120, and 1,000 sec. exposure times. Presence of minimum visible lesions was assessed ophthalmoscopically at both 1 hour and 24 hours after exposure. With increasing exposure times, a 24 hr. lesion-appearance criterion resulted in ED50 values too low to be consistent with a thermal damage mechanism. In contrast, exposure to neodymium laser radiation at a 1,060 nm. wavelength for 120 sec. produced only ED50 values consistent with those associated with thermal injury. These results suggest that the damage mechanisms for long-duration exposures to visible light may involve photochemical processes initiated by the interaction of visible light with the retinal photopigments.

Animals↗
PubMed1977

Histopathology of retinal lesions produced by long-term laser exposure.

The maculae of rhesus monkeys were exposed for 120/s to Nd-YAG and argon laser radiation at wavelengths of 1060 and 514.5 nm, respectively. Histopathology of lesions associated with a thermal and a nonthermal damage mechanism were compared. Differences were observed for both lesion development and retinal layers affected, depending upon the damage mechanism involved.

Animals↗