ABSTRACT
Spectral sensitivity functions for the threshold detection of mesopic incremental targets were compared for different target eccentricities (10, 20, and 30 degrees ) and for different mesopic backgrounds (0.1, 0.5 and 1.0 cd m(-2)). Relative responsivities of achromatic mechanisms (L + M and rods) and chromatic mechanisms (S and /L-M/) were estimated for each eccentricity and background. Chromatic mechanisms contribute significantly to detection but their effect is lower at 30 degrees . A new contrast metric (C(CHC2)) is introduced to account for the selective adaptation of the photoreceptors and the effects of the chromatic mechanisms i.e. broadening of the range of spectral sensitivity with multiple local maxima and yellow sub-additivity of detection performance. The C(CHC2) metric is compared with the achromatic contrast metric of the MOVE model (C(MOVE)). For the same target, C(CHC2) generally predicts a higher visibility level than C(MOVE). However, in accordance with visual observations, for grey or yellowish incremental targets appearing at the eccentricities of 20 and 30 degrees , the visibility predicted by C(CHC2) is less than the visibility predicted by C(MOVE).
Subject(s)
Color Perception/physiology , Sensory Thresholds/physiology , Color Perception Tests , Computer Simulation , Contrast Sensitivity/physiology , Discrimination, Psychological , Humans , Light , Mathematics , Models, Biological , Photic StimulationABSTRACT
Human vision works in a complex way in the mesopic luminance range which is not yet clearly understood, although several important visual tasks are performed at these luminance levels. In this study, spectral data for detection visibility and recognition contrast sensitivity were obtained in visual experiments. From our data it appears that chromatic channels also influence mesopic contrast sensitivity. An achromatic model of spectral sensitivity is fitted to our experimental data and the remaining chromatic components are discussed.
