Usability evaluation of monocular optical head-mounted displays on reading tasks

Abstract

This study explores the factors affecting reading time, error rate, visual fatigue, and mental workload of subjects using a monocular optical head-mounted display (OHMD). Forty healthy participants were involved in this study using four factors: gender, reading conditions (walking and sitting), font sizes (12-, 16-, 20-, 24-, 28-, and 32-point), and contrast ratios (3.0:1, 7.5:1, 12.0:1, 16.5:1, and 21.0:1). The reading time, error rate, critical fusion frequency, the National Aeronautics and Space Administration’s raw task load index, and visual fatigue scale were the dependent measures. Gender showed no significant effect on reading time or error rate. Reading conditions, font sizes, and contrast ratios had significant effects on reading time. Large font sizes produced the fastest reading times for both walking and sitting conditions. The walking condition produced significantly more visual fatigue and mental workload than the sitting condition. Font size and contrast ratio had significant effects on reading time and error rate. The fastest reading time was found at the 16.5:1 contrast ratio for both walking and sitting conditions. Combined with the 28-point font size, we found the fastest reading time and lowest error rate performance combination. Considering reading conditions, contrast ratios, and font size combinations, the 16.5:1 contrast ratio with 28-point font size in the sitting condition and the 16.5:1 contrast ratio with 32-point font size in the walking condition showed the best reading times and error rates. The results from this study can provide very useful reference information for OHMDs and related product interface designs.