The effects of whole-body vibration on the perception of the helmet-mounted display 2 Vols

Abstract

The purpose of this research programme was to investigate the extent that whole-body vibration degrades the perception of the helmet-mounted display, and to determine the causes of this degradation and develop methods for correcting or improving perception during vibration. Initially, the areas of visual perception, display design, aircraft vibration, and biodynamics were reviewed in the published literature. Vibration and display factors were identified which were relevant to the perception of helmet-mounted displays in a vibration environment. An experimental program consisting of 17 experiments was then conducted to address the specific effects of these factors. Character legibility experiments measured the effects of seat vibration frequency and level, display format, character size, background luminance, and contrast on reading performance. Biodynamic studies measured the movements of the head, helmet, and helmet-mounted display as a function of the vertical Z axis vibration of the seat. Movements of the eye relative to the display were determined using a subjective measurement technique. Field trials in a Sea King helicopter extended and verified the results of the laboratory experiments. Additional experiments were conducted to assess the effects of vibration on the perception of simulated sensor imagery, and the evaluation of a simple image stabilization system. The main results of the legibility experiments showed that whole-body vibration caused remarkable decreases in display perception. The magnitude and nature of the degradation were functions of the vibration frequency and level and the display conditions under which the visual materials were presented. There were wide variations in the absolute performance of subjects; but generally, vertical sinusoidal vibration of the seat between 4.0 Hz and 5.6 Hz produced the greatest decrements in perception. The biodynamic experiments showed that the vertical motion of the seat induced rotational motions of the head and helmet primarily in the pitch axis. At some frequencies, there were also large motions of the helmet on the head. Tbe rotational motions of the helmet and head also produced displacements of the helmet-mounted display image on the retina causing perception to degrade. Character reading performance was improved by increasing character size and manipulating background luminances and character-to-background contrasts. Improvements to imagery presentations during vibration were provided by the simple image stabilization system. The overall results of the experimental program were used to establish guidelines for improving the utility of the helmet-mounted display in various flight environments. Areas for additional research were also recommended.

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ORCID for M.J. Griffin: orcid.org/0000-0003-0743-9502

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