Carroll T. White

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.

Effects of contour sharpness and check-size on visually evoked cortical potentials

Abstract Averaged evoked cortical potentials were obtained from S s as they viewed three checkerboard stimulus patterns (checks subtended 12, 20 and 46 min visual angle) through a series of ophthalmic lenses (+6D to −6D). The checkerboards appeared to vary in sharpness of focus under these conditions. Two components of the evoked cortical potential are very sensitive to the sharpness of focus and to the size of the checks in the visual display, a negative one with a latency of 90–100 msec and a positive one with a latency of 180–200 msec. The amplitude of both components decreased as diopter settings were increased and the visual patterns became degraded. The late component was particularly sensitive to check-size under normal viewing conditions. The results suggest that it is possible to determine refractive error by observing the changes in these two components when a stimulus pattern is viewed through a series of lenses.

Latency and duration of eye movements in the horizontal plane.

The electrical method of eye movement recording (EOG) was used to study the reactions of the eyes when subjects attempted to fixate as quickly as possible on light stimuli appearing at various points along the horizontal plane. Each eye was recorded separately, allowing an assessment of the degree of independence of the eyes when reacting in this way. In addition to the data concerning latency of ocular reactions and the duration of eye movements, information regarding the relative speed of movements from periphery to center as compared to movements from center to periphery was obtained. It was also found that the two eyes tend to act independently in regard to latency and speed of movement when moving toward peripheral stimuli.

Perceived Number and Evoked Cortical Potentials

Evoked cortical potentials and the numsber of flashes perceived were compared when subjects were presented with short trains of flashes under conditions where each presented flash could not be counted individually, but the train of flashes appeared to be flickering (1 to 14 flashes at 33.3 flashes per second). The rate at which each successive perceived flash was added appeared to correspond with the rate at which the successive components of the evoked response pattern were added. The temporal nature of this pattern was similar for both single flashes and trains of flashes. The results suggest that the onset of stimulation triggers a process whlich has a marked effect on both the cortical and perceptual response to subsequent stimulation.

Evoked Cortical Potentials: Relation to Visual Field and Handedness

The amplitiude of evoked responses of occipital cortex in man depends on the visual field in which the stimulus appears. Greater responses occurred repeatedly for two of three subjects, both left-handed. when the stimululs appeared in the left field than in the right. Subsequent tests of 13 right- and 13 left-handed males indicted that the magnitude of the response of the right lobe, relative to that of the left, was greater for left-handed individuals. We conclude that the difference in amplitude between the two lobes is related to handedness.

MUSCULAR TENSION, EFFORT, AND TRACKING DIFFICULTY: STUDIES OF PARAMETERS WHICH AFFECT TENSION LEVEL AND PERFORMANCE EFFICIENCY', '

Introduction 33 1 General description of apparatus and experimental procedures 333 Experiment I. Muscular tension level and level of aspiration 337 Experiment 11. Effects of variations in target size and velocity on tracking performance and muscular tension level: a preliminary study . 340 Experiment 111. Effects of variations in target size and velocity on tracking performance and muscular tension level: an intensive study ... 342 Part A 343

Activation and Behavior: II. Visually Evoked Cortical Potentials in Man as Indicants of Activation Level

The effects of variations in behavioral arousal and neural activation or excitation on averaged evoked occipital-cortical potentials to a repetitive flashing light stimulus were studied, using the Mnemotron computer of average transients (CAT). Degree of behavioral arousal and neural activation was manipulated by having Ss perform physical and “mental” tasks of varying degrees of difficulty. Records obtained under these conditions were compared with those obtained during periods of physical and mental quiescence wherein activation level was assumed to be at a relatively low level. The evoked potential patterns were found to increase in amplitude and/or to change in wave form with increases in level of activation or arousal. A number of techniques for quantifying differences in evoked cortical potential patterns were described. It was concluded that the evoked potential measure may be added to the repertory of physiological measures (EEG, EMG, heart rate, skin conductance, etc.) currently considered to constitute reliable and valid indices of activation level.

Averaged occipital responses to stimulation of sites in the upper and lower halves of the retina

Averaged responses of the occipital lobes to flashes imposed along the midline of the upper part of the retina are larger and of shorter latency than responses to flashes imposed on the lower retina. Since reaction times also are shorter when the upper retina is stimulated, this study provides further evidence for the generalization that reaction time varies inversely with amplitude and directly with latency of the evoked response.

Effects of checkerboard pattern stimulation on evoked cortical responses in relation to check size and visual field

Cortical evoked responses to checkerboard stimulation were studied as a function of check size and visual field. Stimuli were presented to the upper, central, and lower parts of the retina. Regardless of check size, largest potentials were obtained to lower-field stimulation; central-field stimulation yielded intermediate responses; upper-field stimulation produced the smallest responses. Maximal responses were obtained to intermediate check sizes during lower-field stimulation and to the smallest checks during upper-field stimulation. The results suggest that the cortical visual system is more responsive to patterned stimuli appearing in the lower viewing field than in the upper, but that the system may be relatively more sensitive to smaller objects appearing in the upper field.

Evoked Potentials and Correlated Judgments of Brightness as Functions of Interflash Intervals

Computer-averaged evoked potentials were recorded from subjects presented with pairs of flashes having equal light energy but differing in duration of the brief interval separating the flashes. For the experimental conditions studied, the pair was always subjectively fused. Although the brightness did not change noticeably as the interval was varied, the use of the forced-choice psychophysical technique showed that apparent brightness declined with increase in the interval. Analysis of the evoked potentials revealed a correlated change in amplitude and wave form previously demonstrated for changes in flash flux alone.