Yuta Suzuki¹, Shigeki Nakauchi², Hsin-I Liao¹; ¹NTT communication science laboratories, ²Department of Computer Science and Engineering, Toyohashi University of Technology

Intrinsically photosensitive retinal ganglion cells (ipRGCs), which contain melanopsin as a photoreceptor that is maximally sensitive to short-wavelength light (460-480 nm; blue or cyan light), are known to mediate physiological responses such as circadian regulation and the pupillary light reflex. Additionally, previous studies have shown that exposure to blue light improves performance on working memory tasks compared with exposure to amber light. However, it remains unclear whether the improvement in cognitive task performance when comparing blue light with reddish light involves other photoreceptors or blue-specific factors, such as color perception. This study investigates the role of ipRGC activation on working memory performance using a silent substitution method that allows selective manipulation of ipRGC activity while minimizing the influence of LMS cone responses. For each subject (N=26 in total), we designed two metameric lights with different levels of ipRGC activation, both perceived as magenta. These lights were implemented using two projectors and optical filters (e.g., Allen et al., 2018). After completing the color matching protocol, participants performed two blocks of a working memory experiment. Each block consisted of several runs of a 1-, 2-back task under the different light conditions, along with two questionnaires on sleepiness and fatigue ratings. The results showed that the correct rate in the 2-back task was significantly higher under the high-ipRGC light than under the low-ipRGC light. Furthermore, the high-ipRGC light reduced subjective sleepiness and fatigue. Taken together, our results confirm that the effect of ipRGC on working memory performance does not necessarily require perceptual blue. This is consistent with the role of ipRGC in projecting to brain areas involved in working memory tasks. These findings highlight that ipRGC activation can enhance cognitive performance independent of blue light perception, broadening the potential applications of lighting environments to support cognitive function.