John C. Armington

AVERAGED BRAIN ACTIVITY FOLLOWING SACCADIC EYE MOVEMENT.

Since a change of stimulus is required to effect a visual response, and since saccadic eye movements change the locus of the retinal image, the hypothesis was developed that there should be a brain response following saccadic eye movement.- The hypothesis was tested experimentally by averaging the activities following successive saccadic eye movements. A response was found whose characteristics were dependent on illuminance of the stimulus.

Summation of retinal potentials.

The operation of a computer which averages low-amplitude electroretinograms is described. The computer has been used to detect electroretinograms which were recorded in an investigation of area-luminance and stray-light effects within the eye. Large test stimuli were found to be more effective than small for producing responses of fixed size. Although the observers reported that the stimulus spread over much of the retina larger photopic responses appeared when the stimulus was centered on the fovea than on neighboring areas. The waveform of the response was found to depend on both the color and the position of the stimulus on the retina.

EEG frequency and finger pulse volume as predictors of reaction time during sleep loss

Abstract The validity of EEG frequency and finger pulse volume for predicting reaction time increased as sleep loss increased. In general, the EEG showed the highest correlation with reaction time, especially in the 1 sec interval just before and just after the signal. As sleep loss increased, the “lead time” for the EEG increased so that by 50 h of sleep loss, valid predictions of reaction time could be made at least 2–3 sec before the signal. Five out of seven subjects showed a bimodal EEG frequency distribution during sleep loss. For these five subjects, perceptual-motor lapses occurred during periods in which the EEG frequency was in the theta rhythm (4–7 c/sec) range. For two of the subjects whose modal EEG frequency slowed somewhat, but did not have a secondary mode at 4–7 c/sec, neither the EEG nor finger pulse volume could be used to predict reaction time. Finger vasodilation was significantly related to long reaction times during sleep loss, but its contribution to the prediction of reaction time was small.

Properties of evoked visual potentials

Abstract Summed responses to repetitive visual stimulation were obtained from human electroretinogram and electroencephalogram recordings. The evoked occipital responses contained a prominent biphasic response complex. The amplitude and latency of this complex varied with stimulus luminance. Scalp responses were more variable than the low-amplitude electroretinograms simultaneously recorded. At low luminance levels, where a summed electroretinogram could no longer be reliably detected, occipital responses were measurable. The area and luminance of test stimuli were varied and the combinations of stimulus area and luminance which produced summed responses of constant amplitude were determined. The area-luminance relation derived for evoked occipital responses was not identical with that for matching electroretinograms.

A quantitative survey of kappa and alpha EEG activity

Abstract An electronic EEG scorer was used to quantify temporal kappa and occipital alpha EEG activities in 100 normal subjects while they were performing hard and easy tasks with their eyes open and closed. The percent of subjects with various EEG scores was shown, in addition to the average data which were statistically evaluated. The distribution of kappa scores suggests that differences between subjects are quantitative rather than qualitative. Hard tasks, such as adding, tended to give higher kappa scores and lower alpha scores than easy tasks, such as counting and keeping a “blank mind”. The increase in kappa activity on hard tasks was found both with eyes closed and eyes open, whereas the decrease in alpha activity on hard tasks was found only when the eyes were closed. Regardless of task difficulty, both alpha and kappa scores tended to be higher when the eyes were closed than when they were open. The effect of eye condition was much greater on the alpha scores than on the kappa scores. The EEG scores and the findings were highly reliable. Evidence supporting the distinction between kappa and alpha EEG activities was presented. Simultaneous kappa and alpha scores were quantitatively accounted for by assuming that the kappa and alpha activities are independent and occur simultaneously by chance. Small, but statistically reliable, correlations were found between kappa scores and height, weight, education, and anxiety estimates.

Flicker and Color Adaptation in the Human Electroretinogram

Flickering ten millisecond light stimuli have been used to elicit the human electroretingram under conditions of chromatic adaptation. The resulting records have been examined both for participation of photopic and scotopic mechanisms, and for selective wavelength effects. With slowly flickering stimuli (4 flashes per second) the ERG (electroretinogram) exhibited distinct photopic and scotopic components even when recorded from eyes that were well light adapted. More rapidly flickering stimuli (20 flashes per second) elicited pre-eminently photopic potentials. It was found that the adaptation stimuli, depending upon their color, were effective in reducing the sensitivity of one or the other component, but that specific chromatic effects within either component were quite small. The results are discussed in relation to psychophysical data and earlier ERG experimentation.

Detection of the electroretinogram in retinitis pigmentosa

An electronic summating technique has been used to detect low amplitude electroretinograms in advanced cases of retinitis pigmentosa. The electroretinogram was obtained with subjects who could not deteot visual stimuli unless they were within three degrees of fixation. The log sensitivity of the electroretinograms of twelve patients of differing deficit was found to have an approximately linear relation to the log area of intact retina. Evoked occipital potentials were also obtained. The significance of these complicated potentials is discussed.

Electroretinogram in Newborn Human Infants

The electroretinogram of the newborn human shows the x-wave component which was demonstrated by Adrian and others to be a concomitant of photopic visual function in the adult. This finding may provide electrophysiological support for behavioral observations indicating that infants have some color vision and ability to resolve visual stimuli.

Adaptational changes in the human electroretinogram and occipital response

Abstract Human electroretinograms and evoked occipital responses were elicited by stimulating the eye with flickering light. Flashes were spaced at half-sec intervals. A computer was used to obtain average response waveforms. The recordings were examined for changes that occurred during the course of stimulation. A long-term and a short-term analysis were performed. With the long-term procedure the records were examined for changes which occur during successive minutes of a 5-min exposure to flicker. It was found that the average amplitude of the electroretinogram occurring during the first minute of stimulation was larger than that for later times. Clear-cut changes were not apparent in the evoked potentials. With the short-term procedure an investigation was made of the average response train produced by successive spurts of five flashes. It was found that the first flash of a stimulus train produces the largest response both at the retina and the occipital scalp; then there is an immediate reduction in amplitude followed by some recovery.

Chromatic and Short Term Dark Adaptation of the Human Electroretinogram

The human electroretinogram was elicited by test flashes which followed 2.5 sec after the termination of a colored adaptation. Typically, the electroretinogram consisted of a negative wave followed by a double positive deflection. The negative wave gave evidence of mixed photopic-scotopic activity. The first positive wave showed high red photopic sensitivity when elicited by long wavelength test flashes and scotopic sensitivity when elicited by short wavelength test flashes. The second positive wave was scotopic. When mixed photopic-scotopic activity was present, the negative wave showed a higher proportion of photopic activity than did the positive wave. Blue adaptation favored photopic response while red adaptation permitted an increase in scotopic sensitivity.