本篇論文以穩態視覺誘發電位(Steady-State Visual Evoked Potential, SSVEP)為基礎，提出了新的編碼設計方式。一般穩態視覺誘發電位之閃光刺激訊號是以頻率編碼為主，使用者須注視以固定頻率持續閃爍之閃光源來誘發出相對應之穩態視覺誘發電位反應；而本論文所提出之編碼方式同時結合了穩態視覺誘發電位之頻率鎖定及時間鎖定特性，其具有特殊的刺激序列結構，將使得閃光源呈現閃爍與熄滅交錯之狀態，如此即可改善一般穩態視覺誘發電位刺激方式容易造成使用者視覺疲勞與不適感之缺點。以此閃光編碼方式所誘發出之穩態視覺誘發電位能量將呈現與刺激序列週期相對應之週期性變化，因此腦電訊號只要經過適當的數位訊號處理即可計算出穩態視覺誘發電位能量變化之週期，並藉此達到辨識閃光選項之目的。最後，本論文已經藉由實驗證實此編碼方式所誘發之穩態視覺誘發電位確實具有上述特性，且可做為大腦人機介面之閃光選項使用。This study proposes a novel stimulation method for steady state visual evoked potential-based brain computer interfaces (SSVEP-based BCIs). The general SSVEP response is induced by a flicker flashing at a fixed frequency. However, visual fatigue evoked by durative stimuli will reduce the amplitude of SSVEP response and make the user uncomfortable. The new coding approach combined of the frequency-locked and time-locked features of SSVEP can eliminate these disadvantages. The flickers will flash for 1 second and turn off respectively for 0.5, 1 and 1.5 seconds by turns. The cycles of the stimulus sequences may cause the corresponding reaction, and the SSVEP energy may appear as periodic variations. This feature will be used in the classification. Finally, the experiment results demonstrate that the SSVEP induced by the proposed method do have the periodic property and can be used in the BCI system.
