Abstract
Abstract: :
Purpose: To characterize the post-receptoral mechanisms that mediate the pupillary response evoked by chromatic changes in the (Δ;L/L, Δ;M/M) plane of cone-contrast space, and to elucidate the relation between the time course of the response and the underlying cone-interaction. Methods: The pupillary responses to chromatic changes from white were recorded. Test stimulus was a 5° circular field located at the center of a white field (19 14°, 28 cd/m2). Test duration was 3 seconds. Stimulus changes were represented as vectors in the (Δ;L/L, Δ;M/M) plane and specified by their direction and contrast. Results: The pupillary responses are generally characterized by a transient constriction following the stimulus onset, a steady-state constriction phase, and/or a constriction/dilation following the stimulus offset. Steady-state constrictions are obvious for higher test contrasts. They are observed even when the stimulus change generates both luminance decrement and chromaticity change, although luminance decrement alone usually evokes the dilation. Iso-amplitude contours for the ON and steady-state portions of the response mostly lie on parallel lines of +45 degree slope and thus exhibit a similar shape to the psychophysical detection contours. The shape of the iso-amplitude contours does not change much with various criterion amplitudes. Conclusions: The properties of the pupillary response measured in the (Δ;L/L, Δ;M/M) plane can be largely described by an (L-M) process that exhibits subtractive cone-interaction similar to that found in psychophysical chromatic detection experiments. The contribution of the (L-M) process is prominent not only for near-threshold but also for suprathreshold stimuli. An (L+M) process seems to mediate the response to a limited range of stimuli around 45 and 225° directions. Furthermore, the present results suggest that (L-M) cone-opponent signals can generate steady-state as well as transient constrictions.
Keywords: 362 color vision • 535 pupillary reflex