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.
Light- and dark-eyed observers, ranging in age from 17 to 67 years, compared six pairs of sunglasses whose neutral density filters transmitted either 0.8, 2.5, 4.8, 8.9, 15.8, or 91.2% of the light. The sunglasses were worn in bright sunlight both in summer and winter and rated for comfort as to the light-level which they admitted to the eyes. In addition, the observers took a test of resolution acuity with each pair of filters. Observers of both eye colors and of every age group preferred, on the average, sunglasses which reduced the light level to 1000 to 1400 cd/m2. These preferred filters are much denser than typical commercial sunglasses. Resolution acuity declined significantly for the older observers with filters denser than the preferred ones.
The ability of subjects to discriminate the depth of depressions in the snow was conducted at a cross-country ski area. The percentage of correct judgments on an overcast day was significantly greater with yellow goggles than with luminance-matched neutral goggles. This experiment, suggested by the chromatic-achromatic theory of color vision, indicates why yellow goggles are popular despite many previous unsuccessful attempts to prove their effectiveness.
To arrive at transmittance standards for cold-weather goggles, the levels of natural radiation were estimated, and the amounts by which they must be reduced to fall below the damage thresholds for various bands of electromagnetic radiation were calculated. No more than 16% of UV from 320 to 40 nm, and no more than 5% of UV from 290 to 320 nm should be transmitted. If the short wavelengths of the visible spectrum (less than 500 nm) are filtered out, the remaining wavelengths appear to pose no danger. Measurements of the transmittances of a random selection of 13 commercial skigoggles showed that most offer satisfactory protection.
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.