一般而言，穩態視覺誘發電位（steady state visual evoked potential ,SSVEP）的選項方式，其中的各單一選項使用不同頻率閃爍刺激誘發的方式。而本論文中，提出一種新的穩態視覺誘發電位閃爍方法，本研究在單一選項的閃爍刺激中，使用兩個不同頻率誘發的穩態視覺誘發系統，稱為雙頻穩態視覺誘發電位（dual-frequency SSVEP），並經由多個受測者的實驗結果證明本方法的可行性。在實驗的過程中，將受測者的腦電訊號（electroencephalography , EEG）使用傅立葉轉換（fourier transform, FFT）分析，發現受測者的腦電訊號裡，有時含有除了主要刺激頻率以外的訊號，此多出的頻率訊號與兩個主要誘發頻率有對稱的現象，稱為對稱諧波現象（symmetric harmonic phenomena），有助於加強辨識。本研究亦提出一個新的相關性計算方法（correlation method）處理這種雙頻閃爍刺激誘發的腦電訊號。經由實驗中發現，本研究所提出的方法在辨識率方面優於傳統被大量使用的快速傅利葉轉換的方法。此外，本論文將所提出的雙頻穩態視覺誘發電位，加入了多相位編碼的閃爍序列。然而，大腦是一個非線性系統，而腦電訊號是其輸出的訊號。而這種包含不同頻率甚至不同相位的腦電訊號是否可被成功的分析，亦是本研究所探討的重點。This dissertation presents a new steady-state visual evoked potential (SSVEP). Differentfrom the general SSVEP using only one frequency flicker for each selection of flashstimulators, this work uses a dual-frequency flicker. This dissertation verifies the feasibility ofthe proposed method, and the symmetric harmonic phenomena are found in this study. Thenthis dissertation proposes a novel correlation method for frequency recognition ofdual-frequency SSVEP. The results further demonstrate that the proposed correlation method has a higher recognition rate than the widely used fast Fourier transform (FFT)method in the proposed system. Moreover, the dual-frequency embedded with the multi-phase flickering sequences stimulation method is proposed. But the brain is a nonlinear dynamic system, and Electroencephalography (EEG) signal can be regarded as its output. The EEG signals in this dissertation include difference frequencies even phases. However, whether this kind of signals is treated as the meaningful signals is researched.
