Color perception of warning identifiers under normal and simulated microgravity conditions

As space exploration missions extend further and last longer, ensuring astronaut safety in microgravity environments has become a critical challenge. Microgravity induces notable physiological and visual perceptual changes, which pose new challenges for the effectiveness of color-coded warning identifiers in conveying critical information. This study investigates differences in the visual perception of warning identifiers with various color schemes under normal and simulated microgravity conditions, providing insights for the optimized design of warning identifiers. We employed a −6° head-down tilt bed rest (HDTBR) protocol to simulate microgravity and used eye-tracking, skin conductance level (SCL), and subjective evaluations based on the User Experience Questionnaire Plus (UEQ+) to systematically assess the visual perception of eight typical color combinations of warning identifiers under normal and simulated microgravity conditions. Twenty-two healthy participants completed two tasks, namely observing scene images and observing identifier images, under both environments to collect subjective and objective data. The results revealed that under normal gravity conditions, the red background with white text attracted the highest proportion of fixation duration and fixation count, with the highest perceived information efficiency and a high reliability score but relatively low aesthetic ratings. In contrast, under simulated microgravity conditions, the blue background with white text demonstrated greater visual salience, outperforming other combinations in objective fixation metrics, while showing a balanced subjective profile with the highest aesthetic score. Identifiers with black backgrounds performed poorly in both environments. These findings highlight a shift in color perception priorities induced by microgravity and provide valuable insights for designing effective warning identifiers in space stations and other extreme environments.