Luminance-Controlled Pupil Size Affects Word Reading Accuracy

The present study extends our prior visual performance studies to a complex resolution task which is representative of tasks in typical workplace environments: word reading presented at a fixed high contrast (black print on white background), but with varying sized letters.

We examined the effect of pupil size on the letter size-acuity function using accuracy of word recognition as the endpoint. Word reading acuity has been extensively used in vision research as a measure of visual performance and has been shown to correlate well with face recognition and other complex recognition tasks. In this study, the task was shielded from the surround lighting, allowing the luminances of the surround and task to be controlled independently. Two pupil size conditions were compared, where pupil size is controlled by high or low luminance levels of a single surround illurninant. We chose to use a single illuminant to control pupil size to avoid changes in induced color which occur when pupil size is changed by varying the surround spectrum.

The results here for nine subjects, ages 23 to 59, years replicate and extend our prior visual acuity studies using Landolt C tasks, and show again that smaller pupils improve visualsperformance even though task retinal illuminance is substantially reduced. We also found that improvement in visual performance with smaller pupils occurs despite an increased disability glare under the high luminance surround condition. Our results are directly applicable to self-illuminated tasks (e.g., computer terminals) operating with black print on a white background.