Abstract
[Purpose] By presenting a high-contrast grating to one eye, stable ocular dominance can be produced and a stimulus subsequently presented to the other eye would be phenomenally suppressed (permanent suppression). In the previous study, we showed that the pupillary responses to color and luminance changes were significantly attenuated during permanent suppression and suggested that the pupillary responses can be used as an objective index to evaluate interocular suppression (Kimura et al., VSS2007). The present study extended our previous work and investigated how the pupillary responses to grating patterns were affected during permanent suppression.
[Methods] The pupillary response was recorded under both permanent- and no-suppression condition. Permanent suppression was produced by presenting a 10° high-contrast vertical sinewave grating flickered in counterphase at 5 Hz to the right eye. During continuous dominance of the suppressing grating, a test grating of the same size and orientation was presented to the left eye for 400 ms. Spatial frequencies of the suppressing and test gratings were 0.5 or 2.8 c/deg. During the measurement, a 12° white background field of 4 cd/m2 was always presented to each eye. Under the no-suppression condition, only the test grating was presented to the left eye.
[Results and Discussion] The pupillary responses to grating patterns were largely suppressed during permanent suppression. The response amplitudes were reduced over a wide range of test contrast and the responses were generally delayed relative to those under the no-suppression condition. However, the magnitude of the suppressive effects did not clearly depend upon spatial frequency particularly when the test grating of 2.8 c/deg was used. In contrast, the sensitivity loss evaluated with psychophysical detection thresholds was highly selective to spatial frequency. These findings suggest that the visual mechanisms mediating the pupillary suppression are at least partially different from those underlying the perceptual suppression.