Mesopic visual efficiency III: Discrimination threshold measurements

The authors represent a research consortium which has adopted a task performance based approach for nighttime driving to obtain mesopic spectral sensitivity functions. This study describes investigations based on discrimination threshold techniques and compares the results with those obtained from detection threshold measurements. It forms a continuation of `Mesopic models — from brightness matching to visual performance in night-time driving: a review'. 1 The achromatic increment contrast threshold for discrimination of a quasi-static target represents the ability to correctly identify a target which has low contrast with the background and is therefore a highly relevant visual task in the context of nighttime driving. The psychophysical experiments reported here are carried out in the laboratory and in dynamic nighttime driving tests. The spectral sensitivity functions resulting from the discrimination threshold contrast investigations show a significant contribution from the colour-opponent (or chromatic) channels of the visual system. Similar features have been observed in results from investigations using detection threshold techniques.