Kagoshima University · Graduate School of Science and Engineering

Research keywordsmotion perception・image gradient tracking・optical flow・melanopsin vision・contrast sensitivity・audiovisual simultaneity・pupillary pathway phase

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• Takeichi H, Suzuki W, Yamashita W, Hiyama A. . Perception of nonrigid structures from motion using tracking image gradient vectors. . Frontiers in Psychology162025 · 記述言語： 英語 掲載種別： 研究論文（学術雑誌） DOI： 10.3389/fpsyg.2025.1586648
• Chien S.E., Yeh S.L., Yamashita W., Tsujimura S.i. . Enhanced human contrast sensitivity with increased stimulation of melanopsin in intrinsically photosensitive retinal ganglion cells2023 · 記述言語： 英語 掲載種別： 研究論文（学術雑誌） 出版者・発行元： Vision Research The intrinsically photosensitive retinal ganglion cells (ipRGCs) are known to serve non-image-forming functions, such as photoentrainment of the circadian rhythm and pupillary light reflex. However, how they affect human spatial vision is largely unknown. The spatial contrast sensitivity function (CSF), which measures contrast sensitivity as a function of spatial frequency, was used in the current study to investigate the function of ipRGCs in pattern vision. To compare the effects of different background lights on the CSF, we utilized the silent substitution technique. We manipulated the stimulation level of melanopsin (i.e., the visual pigment of ipRGCs) from the background light while keeping the cone stimulations constant, or vice versa. We conducted four experiments to measure the CSFs at various spatial frequencies, eccentricities, and levels of background luminance. Results showed that melanopsin stimulation from the background light enhances spatial contrast sensitivity across different eccentricities and luminance levels. Our finding that melanopsin contributes to CSF, combined with the receptive field analysis, suggests a role for the magnocellular pathway and challenges the conventional view that ipRGCs are primarily responsible for non-visual functions. DOI： 10.1016/j.visres.2023.108271 Scopus PubMed
• Tsujimura S.I., Matsumoto A., Yamashita W. . Intrinsic Phase Difference between Cone and Melanopsin Signals in the Pupillary Pathway . Proceedings - 2023 24th International Conference2023 · 記述言語： 日本語 出版者・発行元： Proceedings - 2023 24th International Conference on Control Systems and Computer Science, CSCS 2023 Humans have adapted to a light environment with natural light in the course of evolution. A novel light environment control system is needed to address the problems of inadequate adaptation to the modern artificial light environment. For a long time, only cone and rod cells were thought to be photoreceptors in the retina (i.e. light sensors in human), but a new photoreceptor was discovered around 2000. These photoreceptors are called melanopsin ganglion cells (ipRGCs: intrinsically photoreceptive retinal ganglion cells). However, at present, the understanding of the functions of melanopsin cells is extremely limited and little is known. For example, many people are getting more sunlight in the morning to improve their sleep quality, wearing blue light-cutting glasses or using the Night Shift function in iOS, suggesting that it is important to activate or inhibit melanopsin cells depending on the light environment, but it is necessary to understand the function of melanopsin cells in order to make appropriate decisions on when to activate or inhibit melanopsin cells. Melanopsin cells have a slower response than cones. They receive signals from classical photoreceptors, indicating that cone and melanopsin signals are integrated at the retina. In the present study, we measured the intrinsic phase difference between cone and melanopsin signals in the pupillary pathway using a silent-substitution technique. The goal of the present study was to investigate how these signals are temporally integrated. We used three different test stimuli: (i) varying melanopsin stimulation without changing L-, M-, and S-cone stimulation (melanopsin stimulus); (ii) varying L-, M-, and Scone stimulation only, without changing melanopsin stimulation (cone stimulus); and (iii) varying the radiant flux of the stimuli, without changing the spectral composition, which reduces or increases the radiant flux uniformly at all wavelengths (lightflux stimulus). Consistent with previous studies, we found a delayed pupillary response to the melanopsin stimulus. The cone signal leads the melanopsin signal by approximately 100 ms in onset constriction of the pupil response. In addition, we measured pupillary responses to the light-flux stimulus, consisting of cone and melanopsin stimuli. The timings of the melanopsin stimuli were set at variable physical phases. When we estimated the intrinsic phase difference from the first harmonic component of the pupil trace, the melanopsin signal leads the cone signal by approximately 32° and the contribution of cone signals is approximately five times greater than that of melanopsin signals at a temporal frequency of 0.5 Hz; this could be accounted for by a linear summation model of cone and melanopsin signals. These results suggest that the intrinsic phase difference between the cone and melanopsin signals is not a simple latency difference between photoreceptors at the retina. The difference in onset time of pupil constriction could be explained by the simple latency difference between cone and melanopsin photoreception, whereas the intrinsic phase difference could be explained by an integration process in the melanopsin receptive field. DOI： 10.1109/CSCS59211.2023.00047 Scopus
• Chien, SE., Chen, YC., Matsumoto, A., Yamashita, W., Shih, KT., Tsujimura, S., Yeh,SL. . The modulation of background color on perceiving audiovisual simultaneity . Visio2020 · 記述言語： 英語 掲載種別： 研究論文（学術雑誌） DOI： 10.1016/j.visres.2020.04.009

• 映像情報の視聴に関する子どもの知覚認知機能発達の解明2024 · 担当区分： 研究代表者
• 視覚的自然場面における人物の動き処理に関する発達過程の解明2021 · 担当区分： 研究代表者 資金種別： 競争的資金
• 非撮像経路信号の制御による脳内明るさ符号化機構の解明2000 · 配分額： 17420000円 （ 直接経費： 13400000円 、 間接経費： 4020000円 ） 平成２９年度には多原色光源表示装置を用いて、瞳孔反射経路における機能解明を実施した。メラノプシン細胞は瞳孔径を制御していることが知られている(e.g.Tsujimura et al. 2010)。本研究で用いる多原色光源表示装置では、任意の刺激パターンの提示が可能である。様々な時空間テスト刺激パターンを提示し、また、同時にメラノプシン細胞や錐体細胞への刺激量を可変することによって、非撮像系経路信号と瞳孔径変化との機能的関連性について検証した。測定は継続中である。本装置を用いることによって錐体への刺激量とメラノプシン細胞への刺激量を独立に制御することにより、瞳孔の対光反射メカニズムを駆動している脳内の明るさ符号化処理がどのように錐体細胞起因の信号とメラノプシン細胞起因の信号を統合しているかを実験的に検証することが可能である。 さらに瞳孔の対光反射メカニズムにおけるメラノプシン細胞と錐体細胞間の潜在的な位相差を測定する実験をおこなった。メラノプシン細胞は錐体細胞よりもその反応が遅いと言われている。瞳孔の対光反射の潜時を測定した実験の成果の一部は、７月に台湾で開催されたアジアパシフィック視覚会議(APCV)、および９月に開催された国際瞳孔学会の招待講演で発表した。国際瞳孔学会では多くの研究者から貴重な意見を得た。平成２９年度の研究成果は論文１件、学会発表５件である。学会発表５件中、１件は国際会議の基調講演（招待講演）であった。
• メラノプシン神経節細胞の視知覚処理における機能の解明2000 · 配分額： 14820000円 （ 直接経費： 11400000円 、 間接経費： 3420000円 ） 本課題では、メラノプシン神経節細胞の視知覚機能への影響について、心理物理学的手法、および神経生理学的手法を用いて明らかにすることを目的とした。先行研究で申請者らが開発した積分球を用いた多原色刺激提示装置を用いて瞳孔の対光反応および様々な視知覚機能の感度を心理物理学的手法、および神経生理学的手法により測定した。実験では研究代表者が先行研究で確立したメラノプシン神経節細胞の独立刺激法を適用した。さらに近年開発した多原色表示装置を改良し、空間パターン刺激を提示し様々な空間周波数刺激条件下でのデータを得た。

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