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Eiji Kimura, Satoru Abe, Ken Goryo; Attenuation of the pupillary response during interocular suppression. Journal of Vision 2007;7(9):51. doi: 10.1167/7.9.51.
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[Purpose] By presenting a high-contrast grating to one eye and a spatially homogeneous field to the other eye, stable interocular suppression can be produced (permanent suppression). The present study investigated the pupillary response to color and luminance changes during permanent suppression and explored a possibility that the pupillary response can be an objective probe of interocular suppression. [Methods] The pupillary response was recorded under both permanent- and no-suppression condition. Permanent suppression was produced by presenting a 3° high-contrast square-wave grating of 2 c/deg to the right eye. During continuous dominance of the grating, a 2.5° test flash was presented to the left eye. The test duration was 100 ms and the flash was ramped on and off over a 100-ms period to eliminate sharp transients. The test direction was defined in the DKL color space (Derrington et al., 1984). During the measurement, a 9.8° white background field of 4 cd/m2 was always presented to each eye. Under the no-suppression condition, the test flash was presented to the left eye while the background field was presented alone. [Results and Discussion] The pupillary responses to luminance as well as color changes were clearly attenuated during permanent suppression. The amount of attenuation was comparable to that determined psychophysically, but the attenuation was observed over a wider range of test contrast extending to well-above the threshold level. However, additional experiments revealed that, in contrast to psychophysical findings, the pupillary response was also attenuated in a similar fashion when the test flash was superimposed on the suppressing grating in the same eye. These findings suggest that the pupillary response can be used to evaluate the interocular suppression but the pupillary suppression would be mediated by a distinct visual mechanism such as the subcortical pupillomotor pathway where visual signals from two eyes are also converged.
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