Pupil response to color signals in cone-contrast space.
OBJECTIVE
It is widely accepted that pupil responses to visual stimuli are determined by the ambient illuminance, and recently it has been shown that changes in stimulus color also contributes to a pupillary control mechanism. However, the role of pupillary responses to chromatic stimuli is not clear. The aim of this study was to investigate how color and luminance signals contribute to the pupillary control mechanism.


METHODS
We measured pupillary iso-response contours in M-and L-cone contrast space. The iso-response contours in cone-contrast space have been determined to examine what mechanisms contribute to the pupillary pathway. The shapes of the iso-response contour change when different mechanisms determine the response.


RESULTS
It was shown that for all subjects, the pupillary iso-response contours form an ellipse with positive slope in cone-contrast space, indicating that the sensitivities to the chromatic stimuli are higher than those for the luminance stimuli. The pupil responds maximally to a grating that has a stronger L-cone modulation than the red-green isoluminant grating.


CONCLUSIONS
The sensitivity of the chromatic pathway, in terms of pupillary response, is three times larger than that of the luminance pathway, a property that might have utility in clinical applications.
Tsujimura
Sei-ichi
S
Department of Bioengineering, Kagoshima University, 1-21-40 Koorimoto, Kagoshima 890-0065, Japan. tsujimura@be.kagoshima-u.ac.jp
Wolffsohn
James S
JS
Gilmartin
Bernard
B
D003118:Color Perception / Q000502:physiology*; D015350:Contrast Sensitivity / Q000502:physiology*; D006801:Humans; D008027:Light; D011680:Pupil / Q000502:physiology*; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*