Abstract
The natural blind spot (BS) in the visual field has been known as a region, where our visual system cannot receive any optical input. The BS corresponds to the optic disk on the retina where ganglion-cell axons converge and leave the eye as the optic nerve and no rod/cone photoreceptors exist. Therefore, we cannot register any visual signals if they are presented inside the BS focally. Recently, we found that the light illuminating inside the BS enhances pupillary light reflex (PLR), even though it cannot trigger PLR by itself (Miyamoto and Murakami, 2015), suggesting possible existence of a physiological mechanism that receives light inside the BS, or more specifically, melanopsin expressed along the axons of ipRGCs in the optic disk. However, it is unknown if the light illuminating the BS, which contributes to PLR, also affects our visual perception. Here, we addressed this question by visual psychophysics on brightness matching. Two white stimuli, each of which covered a part of the right or left visual hemifield (eccentricity: 5–10 deg), were sequentially presented briefly (duration 50 ms; SOA 150 ms). Participants were requested to judge if the second stimulus (test) was brighter than the first one (reference) by 2AFC. In half of the trials, the test stimulus was accompanied by a bluish oval presented inside the BS, and its effects on the luminance of the test stimulus at the point of subjective equality (PSE) were examined. We found that the test stimulus was judged as darker (t(7) = 3.48, p = 0.010) with the oval inside the BS than without it. Moreover, there was a slight indication that the oval inside the BS led to PLR enhancement, just as in the previous study. These findings suggest contributions of some physiological photo-sensitive mechanism inside the optic disk to our image-forming vision.
Meeting abstract presented at VSS 2017