眼球運動 Oculomotor System
P1-1-90 自動車運転中のマイクロサッカードと超短間隔Square wave jerkの評価 Evaluation of microsaccades and ultra-short-interval square wave jerk during car driving ○三木俊太郎1, 平田豊1 ○Shuntaro Miki1, Yutaka Hirata1 中部大・工・情報工1 Dept. Computer Science, Chubu University College of Engineering, Aichi, JAPAN1 Microsaccades are fixational eye movements that are involuntarily produced during attempted visual fixation. Recently the relationship between the properties of microsaccade and attention has been studied intensively in laboratory environment. However very few attempts have been made to evaluate microsaccades under more natural visual conditions, such as during car driving. In the present study, we recorded binocular eye movements of human subjects by using portable video eye tracking system (EyeSeeCam, Univ. of Munich Hospital) while they were driving a car on the road, and evaluated their microsaccades to argue the usefulness of microsaccade in estimating car driver's attentional states. It was found that microsaccades indeed occur under the car driving condition, and the number of microsaccades changes depending upon road situation. Namely, more microsaccades are generated when more cars and pedestrians are around. We further found peculiar microsaccade-like small eye movements that consist of a small saccade followed immediately by another small saccade in the opposite direction with almost identical size. Although their bi-directional nature is similar to square wave jerk, the interval between the 1st and the 2nd microsaccade seems much shorter than that of ordinary square wave jerk. Thus in our presentation, we shall call them ultra-short-interval square wave jerk, and compare their characteristics in relation to subject's spatial attention with those of ordinary square wave jerk and other microsaccades that were recorded both during car driving and a common visual fixation task in the laboratory.	P1-1-91 EOGとVOG同時計測による固視微動の同定 Identifying the fixational eye movements with simultaneous EOG and VOG ○田中靖人1, 藤江博幸2, 玉田靖明2, 藤江龍登2 ○Yasuto Tanaka1, Hiroyuki Fujie2, Yasuaki Tamada2, Ryuto Fujie2 神経数理学研究所1, 株式会社　三城　R＆D2 Neuro Mathematics Laboratory1, Miki Inc. R&D Kobe Japan2 Our eyes move microscopically even when we fixate a static visual image. Recent studies show that such eye movements are critical to our visual perception. Although fixation eye movements arguably consist of three different types: (1) flick (microsaccade), (2) drift, and (3) tremor, little is known as to their spatial and temporal details in classification. Here we developed a system to identify three different types of movements by conducting simultaneous measurement of video oculogram (VOG) and electro-oculogram (EOG).VOG was obtained by focusing images on vessels on the sclera using the ultra-high speed camera (300Hz) and the macro conversion lens. EOG was acquired by a traditional electrode placed vertically and horizontally across eye ball. Temporal precision was assured by giving independent trigger signals to the system. Video images are processed by SURF (Speed-Up Robust Features) object tracking algorithm to extract a feature of the x-y coordinate of image motion. The VOG and EOG signals were analyzed statistically by the Fourier and the Wavelet transforms. Human observers (a) fixated a static fixation point (fixation task), and (b) tracked a fixation point that shifted either vertically and horizontally by a degree (tracking task). Frequency analysis (fast Fourier transform) on the EOG signal extracted fast movements of tremor (frequency=30 to 150Hz) with continuous occurrence, which was assured by discrete Wavelet analysis. Furthermore, the VOG tracking resulted in stochastic movements of drift (Brownian motion, magnitude=8.0 to 32.0 minarc) as well as occasional flicks (magnitude=24.0 to 120.0 minarc) in both tasks. These results demonstrate identification of the three fixational eye movements with appropriate temporal precision and spatial resolution.
P1-1-92 ラット内側前庭神経核と舌下神経前位核のコリン作動性ニューロンのニコチン性電流応答の薬理学的解析 Pharmacological analyses of nicotinic current responses in the rat medial vestibular and prepositus hypoglossi cholinergic neurons ○張月1, 柳川右千夫1, 齋藤康彦1 ○Yue Zhang1, Yuchio Yanagawa1, Yasuhiko Saito1 群馬大学大学院　医学系研究科　遺伝発達行動学1 Department of Genetic and Behavioral Neuroscience, Gunma University Graduate School of Medicine1 Cholinergic system in the medial vestibular nucleus (MVN) and prepositus hypoglossi nucleus (PHN) plays important roles in horizontal eye movements. Using whole-cell recordings in brainstem slices obtained from choline acetyltransferase (ChAT)-tdTomato transgenic rats, we have previously found that local pressure application of acetylcholine (ACh) induced inward currents in cholinergic neurons in the MVN and PHN. The inward currents consisted of both muscarine- (Mus) and nicotine-sensitive (Nic) currents, and the Nic currents (1.8 ± 1.9 pA/pF) were larger than Mus currents (0.6 ± 0.5 pA/pF; n = 16; p = 0.02). In the present study, to clarify subtypes of nicotinic ACh receptors (nAChRs) responsive to Nic currents, we performed pharmacological analyses of Nic currents in MVN and PHN cholinergic neurons. The Nic currents were separated into three types based on their activation and desensitization kinetics; Nic currents exhibiting fast kinetics (type I), slow kinetics (type II), and a combination of fast and slow kinetics (type III). Pharmacological analyses revealed that type I and II were mostly blocked by methyllycaconitine (MLA), a specific antagonist of α7 nAChRs and dihydro-β-erythroidine (DHβE), a preferential antagonist of α4β2 nAChRs, respectively (type I: 97.7 ± 2.1% of control, n = 5; type II: 70.3 ± 7.3% of control, n = 8). The type III was blocked by MLA plus DHβE. These findings indicate that type I and II of Nic currents are mostly mediated by α7 and α4β2 subtype of nAChRs, respectively, and type III is mediated by both α7 and α4β2 subtypes. All these results suggest that cholinergic neurons in the MVN and PHN show distinct cholinergic responses, dependent on the expressions of α7 and/or α4β2 nAChRs.	P1-1-93 ヒトの注視行動に影響を与える要因：自然風景に物体画像を配置した複雑な刺激画像による解析 Factors affecting human gaze behavior during free viewing: an analysis with complex natural scenes with superimposed object images ○鈴木実佳1, 山根ゆか子1, 伊藤淳司2, 向将充1藤田一郎1田村弘1 ○Mika Suzuki1, Yukako Yamane1, Junji Ito2, Masamitsu Mukai1, Serge Strokov2, Ichiro Fujita1, Pedro E. Maldonado3, Sonja Gruen2,4, Hiroshi Tamura1 大阪大院・生・認知脳研1 Grad. Sch. Front. Bio., Osaka Univ, Osaka1, INM-6, Forschungszentrum Jülich, Germany2, Progr of Phys. Biophys., Fac. Med., Univ. Chile3, Theoret. Syst. Neurobio., RWTH Aachen Univ, Germany4 Humans perform frequent saccadic eye movements to scan a scene, gaze at an object at a time, and collect visual information from the environment. To study gaze behavior under free viewing conditions, images of natural scenes have often been used as visual stimuli. However, because natural images contain many components and their visual characteristics are difficult to quantify and control, it remains unclear what factors of a scene determine the direction of observer's gaze. In this study, we placed images of 3-10 objects (flowers, human faces, animals, etc., selected from 10 images) at selected positions over natural scene backgrounds (34° × 26°, 4 scenes). With this procedure, we could control conspicuousness of the superimposed objects by manipulating their position, size, and number. We calculated a contrast index defined as the mean difference of RGB values of an object image and those of a patch of background occluded by the object. The index will be low if an object and an occluded patch are similar. In these cases, the object image looks merged into background, because a patch of a scene is in general visually similar to a surrounding region (i.e., the structure of natural scenes is locally correlated). We analyzed eye movements of subjects during free viewing of such scenes with experimentally added objects. Subjects fixated more often on objects with a high contrast index value than on objects with a low index value (p < 0.01, χ2 test). Among the objects added, the subject's first fixation was more often directed towards an object of a higher contrast value (p < 0.05, randomization test). The contrast index value thus allows us to predict gaze position to some extent. However, gaze position was also influenced by other factors; an object near the center of the image was more often fixated than those in the periphery, and human faces attracted subject's gaze more often than other objects of a similar or even higher contrast index value.
P1-1-94 サル前頭眼野の注視ニューロンの活動とその滑動性眼球運動の抑制との関係 Activity of fixation neurons in the monkey frontal eye field and its relation to the suppression of smooth pursuit eye movements ○伊澤佳子1, 鈴木寿夫1, 篠田義一1 ○Yoshiko Izawa1, Hisao Suzuki1, Yoshikazu Shinoda1 東京医科歯科大学大学院 医歯学総合研究科 システム神経生理学1 Dept Systems Neurophysiol, Tokyo Medical and Dental Univ, Tokyo, Japan1 Focal electrical stimulation in the frontal eye field (FEF) suppresses the generation of saccadic and smooth pursuit eye movements at an intensity lower than the threshold for eliciting electrically evoked saccades. We previously found a localized area of the FEF in the caudal part of the arcuate gyrus facing the inferior arcuate sulcus in which stimulation suppressed the generation of saccades and smooth pursuit in bilateral directions and also where fixation neurons discharging tonically during fixation were concentrated. The present study analyzed the activity of fixation neurons in the FEF during smooth pursuit in trained monkeys. Fixation neurons showed a variety of discharge patterns during smooth pursuit, ranging from a decrease in activity to an increase in activity. Of these, more than two thirds of fixation neurons were found to show a reduction in activity during smooth pursuit toward ipsilateral or bilateral directions. The reduction in activity of fixation neurons began at pursuit initiation and continued during pursuit maintenance. When catch-up saccades during the initiation of pursuit were eliminated by step-ramp target routine, the reduction in activity of fixation neurons survived. The present results suggest that fixation neurons in the FEF may contribute to the generation of smooth pursuit suppression. These findings support the idea that this type of fixation neuron assembly as a whole in the FEF may be part of the more generalized visual fixation system with which suppressive control of smooth pursuit as well as saccades is performed.

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