Color vision with rapid-onset acceleration.

INTRODUCTION: Only sporadic information exists concerning perceived color shifts at increased G-loads. The purpose of this study was to investigate whether or not color vision is affected by rapid onset high G7-loads up to +9 Gz, and specifically whether perception of hue changes. METHODS: There were 10 male subjects, 9 with normal color vision and 1 with red-green protanomaly, all accustomed to Gz-loads in a human centrifuge. Each subject was tested on a total of 60 Gz-exposures with 10 s periods at +3, +5, +7, and +9 Gz in the centrifuge on three different days. G-onset rate was 6 G x s(-1). The subjects wore an anti-G suit and performed straining maneuvers if necessary to maintain vision. Five square color stimuli of medium saturation (yellow, red, blue, green, and gray) were projected one at a time on a screen in front of the subject, who gave his hue response orally. RESULTS: In 96.6% of exposures to various Gz-loads, the subjects responded by correctly naming colors. (The statistical analyses of the results were done for the subjects with normal color vision, with the protanomalous subject excluded.) Hue shifts occurred at the higher +Gz-levels, including 7.7% of the +9 Gz exposures. Yellow was the hue most frequently perceived as changed. Hue shifts were reported for yellow in 11% and 16% of the +7 and +9 Gz exposures, respectively. Hue shifts at +9 Gz occurred as frequently as blackout and G-LOC together. However, statistical analyses showed no significant effects for +Gz-load. CONCLUSIONS: Absolute identification of the color stimuli of medium saturation was stable and was not significantly affected by the rapid onset +Gz-loads up to and including +9 Gz.

Effects of normobaric hypoxic confinement on visual and motor performance.

INTRODUCTION: The use of reduced oxygen levels has been suggested for fire prevention in closed spaces, such as submarines. However, if humans are to work and live in environments with reduced oxygen levels, the effect of hypoxia on human performance must be further assessed. METHODS: In 3, 11- to 14-d confinements a total of 22 subjects were exposed to different levels of normobaric hypoxia (13, 14, and 15 kPa O2), for up to 10 d, with intervening periods of normoxia. In each experiment eight subjects were divided into two teams, working in 6-h shifts around the clock. Subjects performed tests of spatial orientation, visual reaction time, parallel processing and motor skills. Performance tests and questionnaires were administered once or twice in every 24-h period. RESULTS: All of the subjects appeared to tolerate the acute reduction in oxygen partial pressure well. In many of the tests performance improved with time as a result of learning, despite reductions in the oxygen level. No reduction in performance or decrease in rate of learning was observed at any of the oxygen levels tested. CONCLUSIONS: Oxygen levels down to 14 kPa appear not to impair visual and motor performance during rest.

Central and peripheral normal contrast sensitivity for static and dynamic sinusoidal gratings.

Contrast sensitivity for moving and stationary sine grating patterns was determined in central and peripheral parts of the visual field. The method was primarily developed as a possible screening procedure for visual defects in glaucoma. Contrast sensitivity to moving patterns seemed maximal both in central and in 10 degrees of eccentric viewing for square wave reversals of temporal frequencies 0.5-5 Hz. We selected 2Hz for the clinical procedure. Further, we have determined normal central and peripheral contrast sensitivity in 10 subjects 61-71 years-old, to serve as a basis for the glaucoma studies. We used this age group since glaucoma mainly affects elderly people. We confirmed that contrast sensitivity was higher for dynamic than for static presentation of gratings of low spatial frequencies (below 1 c/d) both centrally and peripherally. For patterns of medium or high spatial frequencies, dynamic and static stimuli were equally detectable. The absolute level of contrast sensitivity was higher centrally than peripherally in the interval 0.3-4 c/d. The lower visual hemifield exhibited greater sensitivity, for both static and dynamic gratings, than the upper one.

Picture simulation of contrast sensitivity in organic and functional amblyopia.

We have tried to illustrate some contrast sensitivity defects by picture simulation. We have used data obtained from 2 patients: a woman with optic nerve lesion (Snellen VA 0.5) and a 7.5-year-old boy with anisometropic amblyopia (VA 0.6). The optic nerve lesion was represented by profound contrast sensitivity loss for all spatial frequencies, while the anisometropic eye showed loss only at high spatial frequencies. A positive picture was decomposed into 1.25 X 10(6) pixels (picture elements), using a drum scanner. In a computer each spatial frequency component of the picture was multiplied by the ratio between the patient sensitivity value and that of an age-matched reference group and a modified image was processed. The pictures illustrate the poor image quality that is associated with general contrast sensitivity loss, even when Snellen visual acuity is only moderately impaired.

Age variations in normal human contrast sensitivity.

The visual contrast sensitivity (the reciprocal of contrast threshold) was studied as a function of age. Psychophysical measurements of binocular and monocular contrast thresholds were made for 33 normal observers at spatial frequencies within the range 0.5 to 40 cycles/degree. The observers were divided into three different age groups: young, middle-aged, and old subjects with the age ranges 6--10 years, 20--40 years, and 60--70 years, respectively. All observers had healthy eyes, normal vision, and Snellen visual acuity of 1.0 or better in both eyes. In all groups, contrast sensitivity for binocular and monocular viewing peaked at a spatial frequency around 3--5 cycles/degree and showed the typical attenuation at low and high spatial frequencies. The binocular contrast sensitivity was higher than the monocular. There was no significant difference between young and middle-aged subjects with regard to contrast sensitivity. Subjects aged 60 years or more showed significantly lower contrast sensitivity than younger subjects for most spatial frequencies above 4 cycles/degree. We may thus conclude that both the binocular and monocular contrast sensitivity seemed independent of age within the range of 6 to 40 years. For higher ages studied (above 60 years), there was a loss of sensitivity in the middle and high frequency regions.