Seiji Nishifuji

Automatic on-line measurement of ship's attitude by use of a servo-type accelerometer and inclinometers

For an accurate automatic on-line measurement of the ships attitude the paper develops an intelligent sensing system which uses one servo-type accelerometer and two servo-type inclinometers which are appropriately located on the ship. By considering the dynamics of the servo-controlled rigid pendulums of the inclinometers, linear observation equations are derived on the rolling and pitching signals of the ship. Moreover, one accelerometer is utilized to extract the heaving signal. Through the introduction of linear dynamic models and the linear observation equations for the three signals, their online measurement is reduced to the state estimation of the linear dynamic systems. A bank of Kalman filters is used to execute the on-line state estimation and to overcome changes in parameters in the dynamic models with time lapse.

EEG recovery enhanced by acute aerobic exercise after performing mental task with listening to unpleasant sound

The present paper investigated response of electroencephalogram (EEG) to aerobic exercise with low intensity after performing mental task with listening to acoustic stimuli in order to measure a recovery effect of the acute exercise on the EEG. The mean amplitude of the alpha wave (8–13 Hz) was significantly reduced during performing mental arithmetic and/or listening to 5 KHz unpleasant tone. In particular, the mean reduction rate of the amplitude was more than 20 % in the low-frequency range of the alpha wave (8–10Hz) under both stressors. On the other hand, the alpha wave was fixed after an acute exercise of 20 min; the mean amplitude of the alpha wave exceeded 30 % of spontaneous level prior to stressed conditions in the low-frequency range but unchanged in the high-frequency range. Response of the theta wave was similar to the low-alpha wave, while beta and gamma waves showed no significant change in response to the stressors and exercise. The observation indicates that the acute exercise with low intensity may be responsible for the rapid recovery and enhancement of the alpha wave in the low-frequency range and theta wave.

Automatic on-line measurement of dynamic ship's attitude

For an accurate automatic online measurement of ships attitude we develop an intelligent sensing system which uses one servo-type accelerometer and two servo-type inclinometers, which are appropriately located on the ship. By considering the dynamics of the servo-controlled rigid pendulums of the inclinometers, linear observation equations are derived on the rolling and pitching signals of the ship. Moreover, one accelerometer is utilized to extract the heaving signal. Through the introduction of linear dynamic models and the linear observation equations on the three signals, their online measurement is reduced to the state estimation of the linear dynamic systems. A bank of Kalman filters are used to execute the online state estimation and to overcome changes in parameters in the dynamic models with time lapse.<<ETX>>

Evidence of stochastic resonance of auditory steady-state response in electroencephalogram for brain machine interface

Stochastic resonance is a phenomenon observed in nonlinear systems for which random noise with optimal level amplifies a weakly periodic signal. In some biological systems, stochastic resonance has been found to be utilized to improve signal transmission. Recently stochastic resonance have been evidenced in photic-driven human electroencephalogram (EEG) and demonstrated to improve performance of brain machine interface (BMI) based on steady state visual evoked potentials. The present study is aimed at giving evidence of stochastic resonance behavior in human auditory steady state response (ASSR) in EEG for developing a high-performance auditory BMI available without visual function. Seven healthy subjects aged 21-24 years old with normal hearing ability participated in the experiment in which their EEG responses to sinusoidally modulated tone with modulation frequency of 40 Hz contaminated by random noise were measured over the entire scalp with varying the carrier frequency (500 and 4,000 Hz), sound pressure of the tone (40-60 dB) and the random noise level (0-50 dB). In four subjects, ASSR amplitude showed a bell-shaped fluctuation with a maximum at noise level of 40 or 50 dB following an increase of noise level, hence the stochastic resonance effect may be elicited in the auditory system. Moreover in the four subjects, we investigated the times when ASSR significantly appeared under two conditions of no noise and the optimal noise that maximized ASSR amplitude. With addition of optimal noise, detection time of ASSR was shortened in three subjects, and ASSR was elicited in other subject. Detection time of ASSR at optimal noise was distributed between three and seven seconds across subjects. These results will be necessary in order to design novel ASSR-based BMIs. Further investigation on the stochastic resonance behavior would provide useful observation for development of auditory BMIs with high classification accuracy by improving the signal to noise ratio in the modulation of ASSR associated with users intent.

Toward binary brain computer interface using steady-state visually evoked potential under eyes closed condition

It is highly difficult for severely amyotrophic lateral sclerosis and heavily spinal cord injury patients to use the brain computer interfaces (BCIs) based on the steady-state visual evoked potential (SSVEP) which need to control the direction of their eye gaze. We investigated amplitude change of the SSVEP associated with mental concentration on flicker to develop the SSVEP-based BCI usable under eyes-closed condition. Under the stimulus conditions of the flickering frequency of 10 Hz and the stimulus intensity of 5 lx, significant difference between the SSVEP amplitude in relaxed state and that in concentrated state was observed in the wide region of the scalp except the left frontal region, while such significance was also seen in the bilateral occipital lobes and left parietal region under the conditions of 14 Hz and 5 lx. Such an impact of mental concentration on the SSVEP amplitude was reproducible.

Impact of mental focus on steady-state visually evoked potential under eyes closed condition for binary brain computer interface

The steady-state visually evoked potential (SSVEP), is found to be affected by mental focusing on the stimuli under eyes closed condition. The amplitude d change of the SSVEP in concentrating on flicker stimuli was investigated for a novel brain computer interface (BCI) based on the SSVEP with eyes closed for severely disabilities who were not able to control their eye movement to use conventional SSVEP-based BCIs. The amplitude of the SSVEP in the posterior region was found to be reduced by more than 20% in 10 out of 11 healthy adults when the subjects concentrated on the flicker stimuli under the conditions of flicker frequency of 10 Hz and stimulus intensity of 5 lx. Such an effect was observed in the occipital region under the condition of 14Hz and 5 lx. These results suggest the possibility of SSVEP-based binary BCI with eyes closed in terms of the mental focus.

Destabilization of alpha wave during and after listening to unpleasant and pleasant acoustic stimuli

Spatiotemporal responses of brain alpha wave to unpleasant and pleasant acoustic stimuli are investigated in terms of the amplitude and phase of the alpha wave. The amplitude of the alpha wave is significantly reduced not only during listening to unpleasant acoustic stimuli but also after listening to the stimuli such as teeth gnashing and a single frequency tone with a frequency of 5 K Hz. Amplitude fluctuation is monotonically increased from the onset to 100 s after the offset of listening to the unpleasant stimuli. Such amplitude instability is also observed during listening to pleasant acoustic stimuli such as classical music and babble of a stream, but is not statistically significant after listening to the stimuli. Temporal phase change rate of the alpha wave is significantly increased during and after listening to the unpleasant acoustic stimuli, whereas it is not significantly changed for the pleasant music. The destabilization effect of the unpleasant stimuli on the alpha wave seems to remain for a longer period than that of the pleasant stimuli.

Spatiotemporal Phase Characteristics of Brain Alpha Wave Entrained to Alternating Red and Blue Flicker Stimuli

We investigate spatiotemporal phase characteristics of the brain alpha waves in the entrainment to red, blue and alternating red/blue flicker stimuli. The alternating red/blue stimuli induce two distinct phase relationships between the alpha waves over the scalp dependent on subjects: 1) an antiphase relationship in approximately half the subjects in which the phases of the alpha waves are in the state of antiphase between the occipital and frontal lobes and 2) an in-phase relationship for the remaining subjects in which the phases of the alpha waves over the entire scalp are almost identical with only small phase differences. In the in-phase relationship, there occurs a phase difference approximately 90 deg between the occipital alpha wave and the alternating red/blue flicker stimuli, whereas the phase difference becomes almost zero in the antiphase relationship. The former anomalous phase response at the occipital lobe triggers the in-phase relationship over the entire scalp.

Phase response of brain alpha wave to temporally alternating red/blue light emitting diode stimuli

Spatial phase response of the alpha wave is investigated under the condition that red and blue flicker stimuli are temporally alternately applied. The alternating stimuli lead to two distinct phase distributions depending on the subjects: 1) a phase reversal, in which the phases of the alpha waves are antilocked between the occipital and frontal regions, and 2) a quasi-phase-locking, in which the phase difference distribution includes the temporal alternation of a phase locking over the entire scalp and the phase reversal between the occiput and front. The result suggests possibilities for the underlying mechanism of the hyper-synchronization of the brain waves seen in photosensitive epilepsy.

Event-related modulation of steady-state visual evoked potentials for eyes-closed brain computer interface.

Brain computer interfaces (BCIs), also be referred to be as brain machine interfaces, transform modulations of electroencephalogram (EEG) into users intents to communicate with others without voice and physical movement. BCIs have been studied and developed as one of the important means for communication-aid between disabled with severe motor disabilities such as amyotrophic lateral sclerosis and muscular dystrophy patients and their caregivers. State-of-art BCIs have achieved the outstanding performance in information transfer rate and classification accuracy. However, most of conventional BCIs are still unavailable for patients with impaired oculomotor control due to requirement of visual modality. The present study aimed at developing a novel 2-class BCI which was independent of oculomotor control including eye-opening using event-related modulation of steady state visual evoked potential (SSVEP) associated with mental tasks under eyes-closed condition. Eleven healthy subjects aged 21-24 years old were recruited and directed to perform each of two mental tasks under an eyes-closed condition; mental focus on flicker stimuli and image recall of their favorite animals, respectively. The magnitudes of SSVEP in the posterior regions of almost all the subjects were seen to be modulated by performing the mental tasks under the conditions of the flickering frequency of 10 Hz and stimulus intensity of 3-5 lx, which was used to express a users binary intent, namely, performing one of the mental tasks or not (rest). The classification performance on the mental focus, 80 %, was larger than that on the image recall, 75 %, in average across all the subjects. Shortening of the data length used for classification would improve the information transfer rate of the proposed BCI.