多彩視覺刺激下人類視網膜黃斑中央窩和黃斑周邊高頻穩態視覺誘發電位反應之比較

Abstract

一般的腦機介面（Brain-computer Interface, BCI）都採用低頻光源來當作刺激源來達到更強訊號反應，但如此低頻率的刺激光源將會帶給受測者視覺疲勞、偏頭痛、癲癇等不良影響。過去已有研究將視覺刺激頻率從5Hz到65Hz以5Hz為間隔，並以刺激黃斑中央窩（視角2°）與黃斑周邊（視角16°-18°）之圖樣來進行完整的探索，證明視覺刺激閃爍頻率高於人類視覺閃爍融合的閥值依然可作為有效的刺激，並降低對於受測者不良的影響，本研究將延伸過去研究色彩上只用單色白光為刺激色彩，將此實驗設計應用於多色光源（紅色、綠色、藍色）來實踐，探索其他顏色光源在高頻穩態視覺誘發電位應用上的可行性和影響性。十位受測者（年齡20-33歲）參與本實驗，利用64通道電極帽擷取腦電訊號，並記錄受測者對視覺刺激主觀的閃爍感受分數。實驗結果顯示特定顏色、頻帶視覺刺激下（紅光：30-35Hz；綠光：10-50Hz），相同刺激頻率比較下黃斑中央窩之訊躁比在統計上顯著大於黃斑周邊之訊噪比，而藍色刺激光源下兩區域無顯著差異。紅、綠與藍光刺激光源下，大部分受測者在刺激黃斑中央窩區域下之閃爍感知分數都是低於刺激黃斑周邊區域。整體而言，若要在高頻維持與低頻視覺刺激下有較佳之訊噪比，且視覺刺激圖樣為黃斑中央窩下，最佳顏色選擇為綠光，紅光次之，藍光則不是較合適的選擇。

It usually used slower frequency visual stimuli to acquire stronger steady-state visual evoked potentials（SSVEP） response to make brain-computer interface（BCI）system more robust. However, such visual stimuli had risk of inducing epileptic seizures and being fatiguing. Previous research studied the SSVEP from retinal foveal and perifoveal in response to a 2 ° circular and a 16 ° –18 ° annular white light stimuli flickering between 5 and 65 Hz by 5 Hz increments. It suggest that lights flashing above human vision flicker fusion thresholds can be potentially used as an effective visual stimuli tool in SSVEP BCI applications. Our research studied SSVEP from foveal and perifoveal of human retina in response to high-frequency polychromatic stimuli. Using red, green, blue LED lights flickering between 5 and 65 Hz by 5 Hz increments as foveal and perifoveal stimuli to induce SSVEP. Ten subjects (age 20-33 years old) participated in this experiment. Their EEG signals were recorded using a commercial 64-channel NeuroScan system. Their flickering perception was also studied. Our results showed in specific combination of color and frequency band (Red: 30-35Hz, Green: 10-50Hz), almost all subjects showed distinctively higher signal-to-noise ratios (SNR) in their foveal SSVEP responses. They also noticed less flickering and felt more comfortable especially blue light. Overall, green is the better color to hold higher SNR in foveal SSVEP response to high-frequency stimuli, followed by red light. Blue is not suitable color to be high-frequency stimuli.