Fig. 2

Identification of cone vision as a function of scene luminance. (a) Percent correct identification of the location of photopically-mismatched but scotopically-matched trials using a three-alternative forced-choice method in normals as a function of scene luminance. Near normal scotopic threshold (7–8 log attenuation), subjects cannot differentiate between door and wall any better than chance. Upon increase in scene luminance, colors become visible and door identification accuracy reaches 100 %. The sigmoidal curve is a logistic function fitted to the data, with parameters θ = −5.01 log (threshold) and σ = 0.28 log (spread). (b) Five GUCY2D-LCA patients that fail to perform the visual orientation task with scotopically-matched trials across the full 8 log unit dynamic range of scene luminances (symbols). Four of the patients successfully orient with unmatched control trials (upper gray bars) over a range of scene luminances suggesting their use of scotopic vision. (c) Two GUCY2D-LCA patients who can correctly perform visual orientation task with scotopically-matched and unmatched trials but require greater scene luminance than normal. Fitted function and parameters as in (A) except for the shifted threshold parameter, which resulted in θ = −3.3 log. Both green/blue and green/red data are shown