Perception Time and Visual Fatigue

An experiment is reported on the times taken to porceive accurately two Landolt rings undor conditions requiring a chango of accommodation from a far to a near distance, to determino whether thero is any inereaso in this time aftor performing a prolongod visual task. This experiment was part of a study of mothods of moasuring visual fatigue. Measurements were made on oight students before and after two-hour periods of sotting a vornier gauge under two different levels of illumination (1 lm/ft2 and 30 lm/ft2). Thero was a significant increase in average time required if the two lovcls of illumination wore considered together. Change of time required did not diffor significantly between the two different lovols of illumination of the vornier gaugo during setting. Contrary to eortain provious work, no average rise in variance of the settings of the vornier gauge was found during the two-honr periods ovor which tho task was continued