David A. Stamper

Task-specific symptomatology changes resulting from prolonged submaximal bicycle riding

ABSTRACTKey Cluster Analysis of 31 selected symptoms in the physical activity questionnaire of Kinsman et al. (9) separated the Fatigue Cluster into two components subsequently labeled General Fatigue and Leg Fatigue. Following prolonged strenuous exercise on a bicycle ergometer at 56% of estimated

Symptomatology Subscales for the Measurement of Acute Mountain Sickness

Additional information regarding the development of symptomatology subscales for the measurement of Acute Mountain Sickness (AMS) is presented. High item intercorrelations and strong factor loadings of items comprising symptom clusters (i.e., Arousal Level, Somatic Discomfort, Tired, and Mood) support the previously reported breakdown of the General High Altitude Questionnaire (GHAQ) into subscales. Rapid transition from low to high altitude resulted in an increase of these symptomatology subscale scores. Several subscale differences were also noted between Phenformin and Placebo Ss at low altitude. Such subscale measures could provide improved estimates of symptomatology, useful in assessing the effectiveness of various treatments intended to ameliorate AMS.

Subjective Symptomatology and Cognitive Performance at High Altitude

Further standardization of the General High Altitude Questionnaire (GHAQ) for use in quantifying the severity of Acute Mountain Sickness is described. The results show, as did an earlier study, the questionnaire reliably reflects changes in symptom severity. The amount of decrement on a number of psychomotor tasks was directly related to the degree of severity of the subjective symptomatology of Acute Mountain Sickness. The results also showed several conceptually clear symptom clusters of the GHAQ that appear to reflect different states of subjective symptomatology.

Laser flash effects on tracking performance and the aversion response

Introduction: For an accidental laser exposure, the duration of the incident radiation on a specific retinal site depends on the initial fixation, the kinetics of the aversion (blink reflex) and the orienting response (eye movement) toward or away from the light image. Pupilary constriction during the exposure will attenuate the retinal irradiance. Methods: In this study, tracking performance was measured in eight volunteers exposed to O1, LO, and 10 second laser flashes while tracking a dynamic target (O28 degs) through a monocular telescope equipped with a miniature video camera to monitor eye response. The collimated 514 nm argon laser beam produced corneal radiant exposures of 0. 16, 0.33, and LO mJ/cm2 for the 0. 1, LO, and 3O second conditions respectively. Total time off target and maximum absolute error scores were measured for bright (430 nits) and dim (43 nits) ambient luminance conditions. Eye response (blink and pupilary response) was assessed by evaluation of the video from the eye camera. Volunteer reports of the visual experience were recorded. Results: Total time off target (> 0.5 mrad) was maximal for the 3 second exposure condition and minimal for the 0. 1 second conditions. Analysis of the data indicated that there was no photic induced blink reflex for the 0. 1 second condition under the bright light condition. For some volunteers, blinks did occur during the longer duration exposures but were not classic reflex blinks. Pupil responses following the laser presentation showed pupil diameters decreased from initial values of approximately 6 mm to 23 mm which reduced the total energy into the eye at that point by a factor of 10. Volunteers reported smeared and multiple afterimages for the 3 second condition, however, only a single, focal, afterimage was reported for the 0. 1 second condition. This information reflects a history of eye movements during the exposure; Summary: For durations of 100 msec or less, physiological mechanisms that would limit the retinal radiant exposure are not operative for the conditions investigated in this study. For the a 1 second exposure condition, fracking performance was not affected for the bright light vials and only minimally affected foe the dim light trials.

Laser-induced afterimages in humans.

Afterimages induced by incoherent light sources have been studied as complex visual perceptions for over 200 years; however, individuals who have viewed a coherent source (a laser) on-axis have reported visual experiences unlike those observed for full-field flashes from incoherent sources. In the present study, 10 volunteers viewed all combinations of blue, green, and red laser light and background colors that matched the wavelengths of the laser sources (a total of 9 conditions). The bright focal (50 μm retinal irradiance diameter) 3-sec. exposures (approximately 9 log trolands-40% of the maximum permissible exposure level) given to the volunteers were administered as they performed a simulator tracking task. A 50/50 mirror (a mirror which reflected 50% of the laser beam into the optical pathway while allowing the 50% of the light from the visual scene to pass through the mirror) permitted simultaneous intrabeam viewing of the laser source and the scene. The volunteers were asked to report what they saw immediately after the laser was turned off and 1-min. postexposure. The immediate reports indicated that the image they observed was the same color as the laser source and not the complementary color. Also, the images were often surrounded by well-defined borders and, regardless of lasers or backgrounds color, were generally red. One minute following presentation of the laser light the images seen were predominantly purple, dark or no longer present; however, the edge color when present generally appeared red. The immediate appearance of the images was inferred to be neural in nature and not photochemical. These results suggest the properties of the laser source, i.e., coherency, monochromaticity, and the lasers capacity to place an intense beam of light in a small retinal area, all contributed to the unique appearance of the postflash images.

Transient disruption of human pursuit-tracking performance for laser exposures below permissible exposure limits

The proliferation of lasers for medical care, laser displays, industrial applications and audio- visual presentations has increased the potential for accidental intrabeam exposure to visible laser radiation. The output of these laser devices may be limited to below permissible exposure limits, but they are perceived as bright and can affect performance. The disruption experienced while viewing a laser is related to factors that include the retinal irradiance level, wavelength, ambient light level and mode (continuous wave (CW) and repetitively pulsed (RP)). This report describes studies where these factors were varied to assess the effects of laser light on tracking performance in a laboratory simulator and in a field study. Disruption was determined by measuring maximum error and total time off target. Performance disruption increased as irradiance levels increased and ambient light levels decreased.Under dawn/dusk conditions, relatively low-level laser energy produced performance disruption. Green laser light at the peak of the photopic sensitivity curve was more disruptive than red laser light. Increased error scores during CW and RP trials were attributed to average rather than peak power effects. More than 1500 laser exposures at levels up to MPE/2 have been given to volunteers. Despite transient performance disruption comparison of the pre- and post- laser visual performance tests and fundus evaluations wee unremarkable.

Effect of Practice Schedule on Two-Hand Pursuit Tracking Performance

40 male subjects, ages 18 to 40 yr., practiced tracking a moving target by manipulating a viscous-damped tracking device using two band grips. Eight subjects were assigned to each of five training groups. Four shortened training schedules that were considered as representing massed, distributed, or a combination of massed and distributed trials were compared with a four-day training schedule which had been previously used. Total practice time was the same for all groups. The subjects tracked a target which was moving in a fixed arc at a constant angular velocity of 5 mrad/sec. Horizontal standard deviation (SD) errors were recorded. Analysis showed significant differences in performance among the groups on a subsequent test day; however, one of the massed/distributed schedules visually showed less variability. Comparison of subjective estimates of “Mental Fatigue” and “Eye Fatigue” among the groups were almost the same. The results are discussed in terms of the schedules most likely to produce stable performance by operators.

Effects of bilateral and unilateral laser ocular exposure in humans

INTRODUCTION: The amount of visual disruption experienced by individuals exposed to a visible laser source at levels, which are below that, which will damage the cornea or retina will depend on laser exposure parameters and task demands. Previous work has evaluated the effects of wavelength, duration, ambient light level, and target variables. One factor that has not received attention is monocular vs. binocular exposure. Whether the exposure is monocular or binocular may alter pupil dynamics, eyelid closure, and ultimately affect visual performance. METHODS: In this study 10 males and females were exposed to 0.1 and 3.0 sec laser flashes while tracking a dynamic target at 0.28 deg/sec through a scope that was capable of selecting binocular or monocular viewing. Bright (430 nits) and dawn/dusk (4.3 nits) ambient light conditions were simulated using ND filters. A collimated 514.5 nm argon laser beam produced corneal radiant exposures of 0.16 and 1.0 mJ/cm2 for the 0.1 and 3.0 sec conditions respectively. For each flash trial total time off target and maximum absolute error scores were calculated. Eye response (changes in pupil diameter) was assessed by evaluation of videotape from an IR eye camera. Tracking error scores (total time off target) were calculated for each flash trial. RESULTS: Analysis of variance results for the total time off target scores found all three main factors (light level, exposure duration, and monocular/binocular to be significant. Earlier studies have previously shown dawn/dusk flash exposures be more disruptive than bright light trials. Also three sec exposures were more disruptive than one sec exposures. Finally, monocular exposures produced significantly higher error scores than did binocular exposures. For the pupil diameters the post-flash diameters were significantly smaller that the pre-flash diameters and monocular diameters larger that binocular pupil sizes. SUMMARY: The Total Time Off Target error scores for the monocular viewing condition were significantly higher than the binocular viewing condition supporting bilateral summation contributions to binocular tracking. Pupil recovery diameters were approximately 84% of baseline for monocular viewing regardless of ambient light level and flash duration. Binocular viewing conditions yielded an average 75% pupil recovery. Continuing analysis of the pupil data precludes us from making a more definitive statement.