The opto-kinetic cervical reflex during formation flight.

BACKGROUND: Weather formation flight is a difficult task prone to episodes of spatial disorientation. Therefore, investigation of sensory reflexes under these conditions is critical. Recent studies have shown that the opto-kinetic cervical reflex (OKCR) occurs during VMC flight conditions and serves to establish the horizon retinal image as a stabilized primary visual-spatial cue. The purpose of this research was to investigate the OKCR and field of view (FOV) during formation flight under VMC and IMC. HYPOTHESES: During VMC tasks pilots will align their heads with the visible horizon, but not under IMC. As FOV is decreased, there will be a significant reduction in OKCR-induced head movement. METHODS: There were 2 experiments conducted in which a total of 26 pilots completed simulated flight tasks in a stationary dome. Head tilt was examined as a function of aircraft bank with unrestricted FOV in Experiment I. Experiment II examined head tilt under three FOV conditions (40 degrees , 60 degrees and 100 approximately circular). RESULTS: During VMC maneuvers pilots exhibited significant OKCR. There were no differences in head tilt between Solo Figure 8 and Formation Figure 8 VMC conditions. Pilots did not tilt their heads under IMC Formation Flight. FOV did not significantly affect the OKCR. CONCLUSIONS: Pilots exhibit the OKCR during Formation and Solo VMC tasks. However, the OKCR is reduced when compared with low level navigation tasks, indicating a difference in the visual cues between tasks. Pilots do not exhibit OKCR during IMC flight; therefore, the OKCR will have an impact on formation flights in and out of clouds leading to sensory conflicts caused by repeated realignment of visual and vestibular systems.

Effects of FOV and aircraft bank on pilot head movement and reversal errors during simulated flight.

BACKGROUND: Recent studies have shown that while flying under visual meteorological conditions (VMC) pilots tilt their head to keep the horizon stabilized on their fovea. This reflex, referred to as Opto-Kinetic Cervical Reflex (OKCR), may improve spatial awareness by establishing the horizon retinal image as a stabilized primary visual-spatial cue. Since the limited field of view (FOV) provided by helmet-mounted displays (HMDs) significantly decreases visual stimuli, the purpose of this research was to determine how reduced FOV affects head movements. HYPOTHESES: As FOV is decreased, there will be a significant reduction in OKCR-induced head movement. Reduced FOV will also increase control reversal errors. METHODS: Twelve pilots completed simulated flight tasks in a stationary dome. Head tilt, pitch, and yaw were examined as a function of aircraft bank and FOV (40 degrees, 60 degrees and 100 degrees circular). The number of control reversal errors was analyzed to investigate signs of spatial disorientation. RESULTS: During VMC manuevers pilots exhibited significant OKCR; however there were no significant differences among the three levels of FOV. FOV significantly affected head pitch movements under both VMC and instrument meteorological conditions (IMC). Pilots yawed their heads in the direction of aircraft bank under VMC. Pilots committed 22 reversal errors out of 72 trials (30.55%). The magnitude of the error was largest for the 40 degrees FOV condition. CONCLUSIONS: Pilots exhibit the OKCR under all tested levels of FOV and also make head yaw movements in order to keep the way point in sight during banking maneuvers. Pilots demonstrated stick reversal errors when transitioning from following a lead aircraft under both VMC and IMC conditions.

Aviation spatial orientation in relationship to head position and attitude interpretation.

BACKGROUND: Conventional wisdom describing aviation spatial awareness assumes that pilots view a moving horizon through the windscreen. This assumption presupposes head alignment with the cockpit "Z" axis during both visual (VMC) and instrument (IMC) maneuvers. Even though this visual paradigm is widely accepted, its accuracy has not been verified. The purpose of this research was to determine if a visually induced neck reflex causes pilots to align their heads toward the horizon, rather than the cockpit vertical axis. HYPOTHESIS: Based on literature describing reflexive head orientation in terrestrial environments it was hypothesized that during simulated VMC aircraft maneuvers, pilots would align their heads toward the horizon. METHODS: Some 14 military pilots completed two simulated flights in a stationary dome simulator. The flight profile consisted of five separate tasks, four of which evaluated head tilt during exposure to unique visual conditions and one examined occurrences of disorientation during unusual attitude recovery. RESULTS: During simulated visual flight maneuvers, pilots tilted their heads toward the horizon (p < 0.0001). Under IMC, pilots maintained head alignment with the vertical axis of the aircraft. CONCLUSION: During VMC maneuvers pilots reflexively tilt their heads toward the horizon, away from the Gz axis of the cockpit. Presumably, this behavior stabilizes the retinal image of the horizon (1 degree visual-spatial cue), against which peripheral images of the cockpit (2 degrees visual-spatial cue) appear to move. Spatial disorientation, airsickness, and control reversal error may be related to shifts in visual-vestibular sensory alignment during visual transitions between VMC (head tilt) and IMC (Gz head stabilized) conditions.

Walking when utilizing a sensory feedback system and an electrical muscle stimulation gait orthosis.

Electrical muscle stimulators (EMS) have been combined with a reciprocating gait orthosis (RGO) to produce an EMS-RGO system for constant velocity ambulation exercise in a spinal cord injured (SCI) individual. The objective of this study is to evaluate an auditory feedback system (AFS) used by the SCI subject when ambulating with the EMS-RGO. Three different types of auditory signals (M = metronome alone, MSL = metronome plus stride length information, and NONE = no auditory feedback) were examined at three different constant walking velocities (WV1 = 0.64 kph, WV2 = 1.22 kph, and WV3 = 1.80 kph). The experimental design was 3 x 3 full factorial with repeated measures, and the dependent variable was the absolute error (AE) of walking distance (absolute value of the distance the subject walked in one minute subtracted from the target distance). A block diagram and circuit schematic of the AFS is provided. The results indicate that at WV1 there is no significant difference of AE among the three auditory conditions (M, MSL and NONE). At WV2, the AE for the NONE auditory condition is significantly greater than the AE for M and MSL (p < 0.05). At WV3, the AE for the NONE auditory condition is significantly less than the AE for M and MSL (p < 0.05). Finally, there was no significant difference in AE between both the M and MSL auditory conditions at any of the three walking velocities. This study indicates that an adequate sensory feedback system for constant velocity control of ambulation in this SCI subject consists of metronome only auditory feedback.(ABSTRACT TRUNCATED AT 250 WORDS)

Effectiveness of the C-Sharp: reducing ergonomics problems at VDTs.

The use of visual display terminals (VDTs) has been associated with complaints of visual fatigue and body discomfort. In an effort to eliminate some of these problems, an ergonomic emphasis has been placed on the design of computer workstations. A new device, the C-Sharp, has been developed to help reduce some of the ergonomics problems related to long-term VDT usage. The C-Sharp was designed to alleviate visual strain and temporary myopia by reducing the amount of muscular work associated with accommodation and convergence to near targets. It was also designed to eliminate glare. The present study is an ergonomics evaluation to determine whether the C-Sharp meets accepted standards and guidelines. Specifically, the objectives of the research are to determine the effects of the C-Sharp on operator reading and search performance, perceived comfort, body posture, and visual acuity. The C-Sharp is compared with mesh-glare filter and no-glare filter device conditions. Subjects were blocked into three groups based on age and type of vision correction (with or without bifocals). Results indicate that the C-Sharp meets the recommendations of the Americal National Standard for human factors engineering of visual display terminal workstations. No differences in objective performance were found between the three glare device conditions. The C-Sharp allowed bifocal wearers to keep their necks in natural postures rather than tilted backwards. Post-session far visual acuity worsened regardless of the device condition.