Kota Sampei

Mental Fatigue Monitoring Using a Wearable Transparent Eye Detection System

We propose mental fatigue measurement using a wearable eye detection system. The system is capable of acquiring movement of the pupil and blinking from the light reflected from the eye. The reflection is detected by dye-sensitized photovoltaic cells. Since these cells are patterned onto the eyeglass and do not require external input power, the system is notable for its lightweight and low power consumption and can be combined with other wearable devices, such as a head mounted display. We performed experiments to correlate information obtained by the eye detection system with the mental fatigue of the user. Since it is quite difficult to evaluate mental fatigue objectively and quantitatively, we assumed that the National Aeronautics and Space Administration Task Load Index (NASA-TLX) had a strong correlation with te mental fatigue. While a subject was requested to conduct calculation tasks, the eye detection system collected his/her information that included position, velocity and total movement of the eye, and amount and frequency of blinking. Multiple regression analyses revealed the correlation between NASA-TLX and the information obtained for 3 out of 5 subjects.

Crosstalk analysis, its effects and reduction techniques among photovoltaic devices used as transparent optical sensors for a wearable line-of-sight detection system

Our group has developed a wearable eye-tracking system that comprises transparent optical sensors on eyeglasses to detect the reflection from the eye and thus, the position of the eye, where photovoltaic cells are used as the sensors. In this paper, crosstalk, or electric interference, among the photovoltaic cells is discussed. The crosstalk makes the neighboring sensors dependent on each other, which leads to large errors in eye-tracking. We experimentally investigated the source of crosstalk by testing different designs of photovoltaic cells and their interconnection. It was revealed that sharing of the electrolyte by the photovoltaic devices was dominant. In addition, overlapping circuits were found to contribute to the crosstalk. We revised the design of the sensors and successfully reduced the crosstalk and improved the accuracy.

Workload Assessment with eye Movement Monitoring Aided by Non-invasive and Unobtrusive Micro-fabricated Optical Sensors

Mental state or workload of a person are very relevant when the person is executing delicate tasks such as piloting an aircraft, operating a crane because the high level of workload could prevent accomplishing the task and lead to disastrous results. Some frameworks have been developed to assess the workload and determine whether the person is capable of executing a new task. However, such methodologies are applied when the operator finished the task. Another feature that these methodologies share is that are based on paper and pencil tests. Therefore, human-friendly devices that could assess the workload in real time are in high demand. In this paper, we report a wearable device that can correlate physical eye behavior with the mental state for the workload assessment.

Examination of human factors for wearable line-of-sight detection system

We proposed a wearable line-of-sight detection system that utilizes micro-fabricated transparent optical sensors on eyeglasses. These sensors can detect the reflection of light from the eye, in which the intensity from the white of the eye is stronger than that of the pupil, and can thus deduce the position of the pupil. LOS detection was successfully demonstrated by using the proposed system, but careful calibration was required for each user. Therefore, in the current study, we investigated the dominant factors that affected the LOS detection accuracy. It was experimentally found that the distance between the sensors on the eyeglasses and the pupil was a dominant factor. Thus, we designed a frame that can be adjusted according to this distance, which enabled LOS detection for all subjects.

Dye sensitized photovoltaic miniaturized solar cells, used as optical sensors for line of sight detection

Dye sensitized photovoltaic devices have been studied as transparent and low-cost solar cells. Our group have miniaturized the cells and used them as transparent optical sensors. This paper reports the design and fabrication of the cells and avoids the cross talk among cells, which was found recently and such effect provokes hardware instability. We use these optical sensors as an eye tracking device. The sensor array detects the difference in the intensity of light reflected from the pupil and the sclera and then determines the pupil position. Each sensor consists of two electrodes and electrolyte; hence our device conformed by only four semi-circular shaped sensors on eyeglasses can detect the view angle in both horizontal and vertical directions. Manufacturing process gives us freedom to easily re-arrange, add or remove sensors. In our prior work we had good performance in stand-alone configuration. We used specialized equipment from National Instruments for our measurements. However we found that: A cell is not 100% independent from the others, is affected by the absence or presence of light at the neighbour cells. When our device is connected to other electronic devices (for data processing), all cells have the same voltage among them; therefore, all cells behave the same way when any of them is affected by light. The root cause is, due to all sensors were interconnected via a micro channel and filled with electrolyte, due to its conductive properties, electrolyte does neither need electrodes nor physical paths to conduct electricity, so it creates a liquid wire between sensors, hence the gap between them become inexistent, consequently when our device is connected to other electronic devices, due to this unique channel and by sharing a common electronic ground, this connection provokes the voltage to be the same among all sensors in the array. Our device becomes four separate voltage lines in a parallel circuit. The device was also in short circuit provoked by some overlapping paths, despite that such paths were in different layers and separated by an adhesive film of 100pm thickness, such thickness was not large enough to creates a successful dielectric to isolate the paths.