異なる輝度の点滅刺激による定常視覚誘発電位の符号化に関する基礎的検討

Abstract

本研究では定常視覚誘発電位に基づくBMI(brain-machine interface)への実用化に向けたSSVEPの符号化に関する基礎的検討を点滅刺激の輝度変調に着目して行った.輝度に応じてSSVEP振幅に符号を割り当てれば, 同一の周波数で区別できる点滅刺激のパターン数が増えると考え, 異なる輝度の点滅刺激に注意を向けた際のSSVEPから, 注意を向けた輝度の点滅刺激を判定できるか否かの検討を行なった.実験は2種類行った.まず, 輝度の異なる4つの12Hzの点滅刺激を被験者に呈示し, 12Hz帯の振幅が最大となる輝度と最小となる輝度を選択した.その後, 選択した2つの輝度の刺激を12Hzで交互に被験者に呈示し, 取得した脳波を全試行間で平均して時間領域と周波数領域において解析した.個人毎にSSVEPの振幅が最大となる輝度が存在することや, 異なる輝度の組み合わせにより実際に用いた点滅周波数以外の周波数成分がSSVEPスペクトルに現れること等が判明し, BMIへの有用な知見が得られた.

In this study, we investigated amplitude modulations of SSVEP elicited by flickering visual stimulus with different luminance towards BMI (brain-machine interface) based on SSVEP. It is possible to increase the number of discriminable stimuli in the same frequency with different luminance. Then, we investigated whether amplitudes of SSVEPs were changed by flickering stimuli with different luminance. We carried out two experiments. First, we presented four flickering visual stimuli with different luminance at random and selected two stimuli which elicited the largest and the smallest amplitudes of SSVEPs. Subsequently, we presented the two stimuli which selected in the first experiment alternatively at 12Hz. The measured EEGs were averaged among all trials and analyzed in time and frequency domains. We showed that there was individual difference luminance for obtaining the maximum amplitude of SSVEP. In addition, different frequency components which was not used as flickering frequency, was observed by a combination of different luminance stimuli. These results may provide useful knowledge to construct a practical BMI.