Biomedical subjects
Publications and source records attributed to S M Luria.
The temporal interval between flashing lights that is required to perceive nonsimultaneity decreases as the refractive error increases from 0 to +2 diopters. The interval then remains constant with further increases to 3 and 4 diopters. The results are discussed in terms of the relative increase of transient to sustained visual channels and of the increase in apparent movement.
Subjects matched the color of a vertical target line, presented in 1 of 10 colors, to a set of 10 colors. The target line was presented either in isolation or together with 5 additional colored lines. Neither mean reaction time nor the number of matching errors increased when the extraneous lines were present, and the types of color confusions did not change systematically.
The temporal interval between flashing lights required to perceive nonsimultaneity increases with decreasing luminance. This explanation appears to lie in the reported changes in the activity of the transient cells in the visual system with changes in luminance.
The effects on dark adaptation of exposure to light presented only in the extreme periphery were significantly greater for observers over the age of 40 years. Increasing the exposure duration from 0.5 to 5 min significantly affected only the older observers.
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Our purpose was to reveal the effects of ambient illumination color and various foreground/background color pairings on a choice reaction time task performed on a color CRT. Six men and two women with normal color vision served as observers in a four-alternative forced choice procedure. A small (18' visual angle) colored circle appeared in the center of one of the unmarked quadrants of the screen. The observer's task was to respond as quickly as possible to this target by pressing one of four buttons corresponding to its location. We found that target colors that were opponent to the background colors were most quickly detected. Detection was enhanced by maximizing both brightness and chromatic contrast, but brightness contrast was much more effective. Chromatic ambient lighting which was a log unit dimmer than the target luminance had no effect on performance.
The problem of escaping from a submerged helicopter is discussed. The effectiveness of illuminated escape hatches in facilitating escape has been demonstrated. The relative advantages of different types of lights are compared. Escape training, illuminating the emergency exits, and providing breathing devices should greatly enhance the chances of survival in a helicopter crash at sea.
1. The effect of three doses of either aspirin (1280 mg each) or dimenhydrinate (Dramamine) (100 mg each) in an 8 h period on visual processes was investigated double-blind on sixteen volunteer subjects. 2. Tests included night-vision, colour-discrimination, stereoacuity and stereopsis, reaction-time, pupil size, eye-movements, visual evoked cortical potentials, electroencephalographs, a dial-reading task, and a test of texture discrimination. 3. Both drugs affected colour discrimination, and dimenhydrinate degraded night-vision, reaction-time, and stereopsis. 4. The effect of aspirin was minor, but the impairments produced by dimenhydrinate appear to be of practical importance.
We had 55 blindfolded scuba divers repeatedly attempt to swim a straight line, make 90 degrees turns to the right and left, and make a 180 degrees turn. A given diver was reasonably consistent in the direction of his error from one trial to another and from one maneuver to another, although about half the divers tended to err to the right and half to the left. When attempted in a swimming pool, the median error over all maneuvers, irrespective of direction, was about 12 degrees. Further experiments showed that the direction of error was consistent, whether the divers were wearing scuba tanks or not, and whether they were swimming blindfolded in a swimming pool or sighted in a lake with water visibility limited to about 2 m. Direction of error did not correlate, however, with the preferred hand, with preferred foot for kicking a football, or with relative strength of the legs. Although hand- and foot-preference were highly correlated, foot-preference was not correlated with relative strength of legs.
A variety of vision tests have been administered to submariners over the years. The results show that the average submariner, though maintaining a normal, healthy visual system, has distant acuity somewhat below normal and manifests more myopia, esophoria, and less accommodative power than men of comparable age, as documented in the literature. The reasons for these changes are unknown but probably involve confinement; whether confinement peculiar to the submarine of the "confinement" of urban living is the more important for these changes is discussed.
The effects of q.i.d. administration of 60 mg pseudoephedrine (Sudafed) tablets or pseudoephedrine-triprolidine (Actifed) tablets after 5 d of medication were measured on tests of night vision, color perception, stereopsis, and reaction time. Neither drug appeared to impair performance.
Eye movements were recorded while subjects viewed ordinary portraits and photographic negatives of those portraits. Under both conditions they first studied sixteen portraits and then tried to decide which of forty-eight portraits they had just seen. They made more errors of recognition while viewing negatives, and their fixation patterns were significantly altered: there was a decrease in the percentage of fixations directed to the eyes, nose, and mouth, and an increase for such details as the ears, cheeks, chin, cap, and necktie. There was also a decrease in the ratio of fixations to the most fixated detail compared to the least fixated detail.
Luminance thresholds were measured for the water-immersed eye as a function of adaptation level, viewing distance, and turbidity of the water, and compared to standard adaptation curves. In water, thresholds varied as a function of initial adaptation level, and the rate of adaptation paralleled that for the eye in air. However, thresholds were about 1-2 log units higher for the water-immersed eye than for the eye in air at all adaptation levels.
Thresholds for letters were measured with and without a masking stimulus (presented either to the same eye as the letters or to the other eye) before and after exposure of smokers and nonsmokers to 500 ppm carbon monoxide (CO) in air for 1 hr. Identification of the unmasked letters was not degraded by CO but a number of thresholds of the masked letters were significantly affected among the smokers. The effects of the CO on binocular and interocular masking were similar. These results suggest that the first effects of CO toxicity are neither on the receptors nor central but on the transmission lines in between and that smokers are more susceptible than nonsmokers to short-term increases in the level of CO. The masking phenomenon, however, does not appear to be an unusually sensitive measure of CO toxicity.
This study is an assessment of individual differences in electrophysiological response under diving conditions normally conducive to nitrogen narcosis. A group of 16 men made two dives each to approximately 200 ft in a pressure chamber while breathing air. The visual evoked response of the men at depth revealed several decrements; in the response to a slow rate of stimulation, there was a highly significant reduction in a component around 160 ms, and in the response to a rapid rate of stimulation, marked losses in amplitude and increases in variability were found. The latter changes were related to diving experience while the former were not. No significant changes were found in alpha or theta activity in the EEG.
Three Navy divers were exposed to a normoxic breathing mixture at 7.0 ATA for seven consecutive days. Visual evoked responses (VER's), electroencephalograms (EEG's) and simple reaction time (RT) were measured. Previously reported amplitude decreases in a VER to a flash rate of 1 Hz (VER 1) and to a flash rate of 16 Hz (VER 16) were again found during this dive. The variability of the VER 16 and the latency of the VER 1 also increased during the saturation period. In the EEG analysis, changes in the amplitude of both alpha and theta were found, as were decreases in alpha frequency. The RT task showed a marked elevation of response time at the beginning of the dive period which gradually returned to predive levels. Latency of the VER 160-180 ms component was highly correlated with the changes in RT. The results are discussed in terms of information processing and cerebral dysfunction.
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Distance and size estimates and stereoacuity judgments were made in water by divers, both with and without facemasks. Without the mask, only stereoacuity was markedly degraded. Distance estimates were slightly more accurate, despite a great decrease in the range of visibility. Size estimates were slightly too small. Divers with refractive errors did not appear to be more handicapped than those with normal vision.