Abstract

Many people with vision loss have difficulty identifying objects encountered in common daily experiences. The measurement of contrast thresholds over a range of spatial frequencies (contrast sensitivity function) has been investigated in low vision observers to explain these difficulties and to recommend techniques for better identification by compensating for reduced contrast sensitivity. However, objects encountered in common daily experiences are rarely viewed in low contrast environments. Although contrast discrimination functions have been shown to be similar in shape and superimposed when normalized by the contrast thresholds in normally sighted observers (e.g., Legge and Kersten, 1987), very little is known about the contrast discrimination function for observers with low vision. That is, while the entire contrast discrimination function can be specified by the contrast sensitivity function for a stimulus in normally sighted observers, it is not known whether this relationship is also true for observers with vision loss. Leat and Millodot (1990) report that contrast discrimination and contrast sensitivity are independent in observers with vision loss. Therefore, it is possible that identification of suprathreshold objects has no relationship to the contrast sensitivity function in observers with vision loss (e.g., Rubin and Schuchard, 1990). The characteristics of contrast discrimination functions in observers with vision loss were studied as they related to the contrast sensitivity functions.

© 1992 Optical Society of America