Relationship between the electroencephalogram, eye-movements and fluctuations of visual perception

Abstract

Relationship between the electroencephalogram, eye-movements and fluctuations of visual perceptionEEG activity and eye movements were recorded while 5s inspected a Ganzfeld or diffuse dark figures introduced into a Ganzfeld. Reports of deterioration of visual perception under all stimulus conditions were preceded by a period of reduced eye movement, but were not associated with a return of EEG alpha activity.Observers report an experience of blank-out or loss of visual perception after a period of exposure to a uniformly illuminated homogeneous field or Ganzfeld (Cohen, 1957). Moreover, areas of inhomogeneous hue or brightness on an otherwise structureless field seem to fade into the background after a time (Guilford, 1927;Cohen, 1958). A similar adaptational mechanism probably underlies both these effects and the fade-out of stabilized retinal images, but evidence from their physiological correlates is unclear. Cohen & Cadwallader (1958) reported that susceptibility to Ganzfeld blank-out was positively correlated with the level of alpha activity in Ss' resting EEG. Tepas (1962), however, found that blank-out periods were little related to alpha activity but were strongly associated with periods of reduced eye-movement. This parallels Guilford's (1927) observation that unstabilized images fade when there is little eye movement, but there are no data to hand on the EEG correlates of this effect. Lehmann et al (1957) reported that the fading of stabilized retinal images is associated with the return of EEG alpha trains in some Ss.The present study investigates the Ganzfeld blankout effect and the fade-out of unstabilized images by simultaneously monitoring both occipital EEG potentials and eye movements using two groups of Ss differentiated on the basis of their levels of resting alpha activity. SubjectsSix young male Ss having no known visual or neurological defect were used. Four Ss showed frequent alpha trains when resting. Two Ss gave fast, low amplitude EEG traces even when resting with eyes closed. ApparatusEEG, electrooculograph potentials, subject responses and time marks were recorded on a Beckman RB dynograph. EEG electrodes were attached with Bentonite at the 10-20 position ipsilateral to the stimulated eye. Eye movement was monitored via 3 mmdisc electrodes placed at the inner and outer canthi of the stimulated

Temporal and spatial factors in the fading of diffuse visual images

“…These results are in-many respects similar to data obtained from experiments with stabilized retinal images, as might be expected from the evidence that the reports of fading of images under conditions similar to those used in this experiment are invariably associated with periods of reduced eye movement (Kirkwood, 1967). Riggs et al (1953) reported that images of fine lines fade more rapidly than those of thick bars when stabilized on the retina.…”

“…Even areas of inhomogeneous hue or brightness introduced into an otherwise uniform field are perceptually unstable and seem to fade into their background after a time (Guilford, 1927;Cohen, 1958;Kirkwood 1967). These effects appear consistent with findings from work with stabilized retinal images.…”

“…2 and 3. All persistence times refer to the initial disappearance of contour following the start of each experimental run; loss of contour vision is usually brief and can be restored by S blinking or making gross eye movements (Kirkwood, 1967). Equating opaque areas in this way permits evaluation of the effect of configuration largely unconfounded by variations in opaque area, although the physical contrast of the smaller dark regions is also reduced relative to the large opaque areas due to the scattering of light within the cap.…”