Anoxia and Brightness Discrimination

Abstract

, I Nature of WorkIt is the commonest of observations both in actual flying and in pressure chamber experiments that fights become dim at high altitudes and then brighten on return to low altitudes. These events are due to the absence and presence of an adequate oxygen supply, as can be shown by their easy elimination when sufficient oxygen is available.The phenomenon itself has been demonstrated quantitatively as a rise in threshold of the dark-adapted eye during anoxia by NicFarland and Evans (1939), by McFarland and Forbes (1940), and by Wald, Harper, Goodman, and Krieger (1942). (C]. also Bunge, 1936, andFischer andJongbloed, 1936.) In addition MCFarland and Halperin (1940) found that visual acuity is affected by decreased oxygen tensions.Brightness discrimination and visual acuity are closely allied visual functions and it is not surprising that Schubert (1932-33) and Gellhorn (1936) detected an influence on brightness discrimination, though they recorded sharply conffieting results. However, McFarland, Halperin, and Niven (1944) have definitely shown that brightness discrimination is impaired by anoxia, and have explored the effect over the significant range of cone vision.Our own work--completed in 1942 but only now available because of its origins---confirms the findings of NicFarland, Halperin, and Niven. Our experiments were made somewhat differently from theirs; theirs cover a greater brightness range, but in most of their work a single low oxygen concentration was compared with room air. We compared seven different oxygen concentrations with room air, at three moderate brightnesses involving cone vision only. II Apparatus and ProcedureIf I is the light intensity of a uniform field of vision, and M is the fight intensity which needs to be added to a part of this field so that the particular *

The effect of a moderate level of hypoxia on human color vision

“…Smith et al found their losses at 371ux whereas we used 175 lux. Previous investigators [15,31,32] report a greater sensitivity of the hypoxic visual system to reductions in illumination than may normally be found at sea level. The study of Bowman and Cole [4] suggests that color discrimination suffers from tritan-like defects somewhere below 10-15 lux at normal oxygen tensions.…”

“…Other authors have also concluded that both the rod and cone systems are affected by hypoxia [15,42] or that cone vision may even have a greater loss than rod vision [11]. Since both the rod and cone pathways are affected by hypoxia there may be some merit in the suggestion that pilots supplement their oxygen supplies in the daytime whenever optimum visual performance is required.…”

“…Many studies evaluating the effects of hypoxia report absolute detection threshold data [11,15,20,32,42,44]. King-Smith and Carden [21] have shown that visual detection of small spots at absolute threshold is mediated by the achromatic mechanism and not by the color-opponent channels.…”

The Threshold for Hypoxia Effects on Perceptual- Motor Performance

“…Part of this slowing was attributed to visual degradation, because response time increased disproportionately when stimulus brightness was lowered. Vision is particularly sensitive to hypoxia (McFarland, 1963), with brightness discrimination showing a definite effect at 8000 feet (Hecht, Hendley, Frank, and Haig, 1946). This raises the possibility that visual factors influence the threshold dose-response function for the effects of hypoxia on perceptualmotor performance.…”

Effects of Hypoxia on Peripheral Visual Response to Dim Stimuli

“…These findings are directly consistent with the severity of exposure, and from the present data are consistent with the contrast relationships of the stimulus surround of the viewing situation. Curiously enough, despite the general finding that brightness sensitivity and dark adaptation are particularly affected by anoxia (hypoxia) (Hecht, et al (1946);McFarland and Halperin (1940)), it would appear that responding throughout the visual field under hypoxia can be greater* for a dim stimulus with good contrast than for other brighter stimuli at higher ambient illumination levels if the latter are at poorer contrast with the surrotmd. Thus, assessment of the effects of hypoxia on visual response must take account not simply of the virtual stimulus luminance, but rather of the functional visibility of the stimulus-background contrast relationships, assuming the stimulus to be above threshold value in the visual periphery.…”