Quantitative assessment of visual acuity in projective head mounted displays

One issue of head mounted display design relates to the tradeoff between field of view (FOV) and resolution, which can lead to reduced visual acuity (VA). Essentially, an increase in FOV causes a decrease in visual acuity, for a given LCD display that has a fixed number of pixels. The effects of enhanced brightness on VA using two different types of retroreflective material (cubed or beaded) were tested using a 52 deg. FOV projective helmet mounted display with VGA resolution. Three lighting conditions were also tested. Based on the display size, resolution, and FOV, we estimated a maximum visual acuity of 4.1 minutes of arc. In a counter-balanced between measures design, subjects' psychometric acuity functions were determined using a computer-generated 4AFC Landolt C test presented stereoscopically and probit analysis. The results confirmed that the maximum visual acuity possible within the setup was 4.1 arc minutes, the limit imposed by the microdisplay, and not the retroreflective material.