Robert G. Eason

Effects of attention and arousal on visually evoked cortical potentials and reaction time in man

Abstract The combined effects of general arousal and specific attention on averaged evoked potentials and reaction time were studied. Arousal level was manipulated by the presence or absence of a shock threat when the flashes were being presented. Attention was varied by having S react to flashes appearing in either his right or left visual field while ignoring flashes appearing concomitantly but not simultaneously in the opposite field. Potentials evoked under “high” arousal (threat of shock) were greater than those obtained under “low” arousal. Also, reaction times were shorter. The potentials evoked by flashes receiving attention were much greater than those evoked by flashes being ignored. The results indicate that cortical evoked potentials are related to both general arousal and specific attention. The combined effects of increasing or decreasing arousal and shifts in attention toward or away from the evoking stimulus determine whether the net change in evoked potential amplitude will be positive or negative.

Evoked Cortical Potentials: Relation to Hand Dominance and Eye Dominance

The amplitude and symmetry of right- and left-occipital lobe evoked potentials (EPs) to right and left visual-field stimulation were studied as a function of hand and eye dominance in female Ss. For all Ss, right-lobe EP amplitudes were greater than left-lobe during left visual-field, but not right visual-field, stimulation. Left-eyed Ss had significantly greater EP amplitudes than right-eyed Ss. Comparing this study with previous ones suggests a sex difference in the relationship of handedness to right lobe-left lobe asymmetry.

Differentiation of retinal and nonretinal contributions to averaged evoked responses obtained with electrodes placed near the eyes

Recent visual evoked potential (VEP) studies suggest that during sustained voluntary attention, irrelevant or unattended visual stimuli may be filtered precortically. Testing of this hypothesis in humans requires knowledge of the origin of specific components of the VEP that are affected by selective attention. This study describes techniques and procedures for distinguishing between retinal and nonretinal components of VEPs recorded from electrodes placed strategically around the eyes and on the forehead. By visually stimulating one eye at a time while recording simultaneously from both, and by stimulating a given retinal area with the eyes fixated on the target at different angular deviations from the normal line of regard, components of the VEPs around the eyes can be distinguished as of retinal or nonretinal origin. The results are discussed in terms of volume conduction theory.

Effect of stimulus size and retinal locus of stimulation on visually evoked cortical responses and reaction in man

A study was made of the effects of variations in the size of a circular light flash presented to each of three retinal areas on the averaged evoked cortical response and reaction time. Flashes varying in size from 0.14 to 20.63 deg of visual angle were centered about the fovea and at distances of 20 and 40 deg from the fovea. Evoked response latency and reaction time varied inversely with stimulus size and directly with distance from the fovea. The initial deflection of the evoked response increased with stimulus size for all retinal locations. Later deflections either decreased, showed no change, or first increased, then decreased with increasing stimulus size, depending on retinal locus of stimulation. The results were explained in terms of areal summation and a model of evoked cortical activity which postulates an alpha-like neural process momentarily controlled by an “extrinsic pacemaker.”

Voluntary alpha control, visually evoked potentials, and peripheral physiological indicants of activation.

To test the hypothesis that voluntary alpha control is mediated in part through self-induced changes in cortical activation level and bodily arousal, changes in several physiological indicants of such activity were systematically examined as a function of the voluntary enhancement and suppression of scalp-recorded alpha activity. Following pre-training, 6 subjects attempted to either produce or suppress alpha with eyes closed while receiving continuous auditory feedback of their alpha levels. The results were interpreted as offering tentative support for the hypothesis.