| 摘要: | 視覺選擇性注意力能?助以有限的能力處理周遭環境，而旁側抑制作業（Flanker task）是研究注意力的經典範式之一。以往研究發現腦電波（Electroencephalography, EEG）頂葉及枕葉α波（約10Hz）在視覺注意力上有抑制干擾物的作用。但是先前研究對α波扮演的作用多來自不同頻率組合間的比較，而非以典型旁側抑制作業為基準。本實驗除了採用無閃動及在目標和干擾位置上增設不同頻率閃爍的旁側抑制作業（如: 6 Hz、10 Hz 或15 Hz），觀察受到不同頻率調控後的表現，並加入目標物和干擾物均為10Hz情況作為刺激閃爍控制組，以進一步探索10Hz α波在注意力中的作用。
結果發現：
(1) 15T|10F（T跟F分別代表目標物和干擾物: 15T|10F 表示15 Hz目標物伴隨 10 Hz干擾物）下整體反應時間不僅比10T|15F短，也比10T|10T和無閃動的情況快；但6T|10F和10T|6F的對比中沒有類似情況。
(2) 10T|15F的一致性效果 (congruency effect) 造成的反應時間差異比其他的情況更長。
(3) 使用全息希爾伯特頻譜（Holo-Hilbert Spectral Analysis, HHSA）分析後發現3 ~ 4 Hz震幅調控10Hz的穩態視覺誘發電位（Steady State Visual Evoked Potential, SSVEP）強度會受注意力調控，但只在15Hz的組合中有顯著差異。
(4) 在10T|10F、10T|6F和6T|10F調控的情況，SSVEP 10Hz的強度與反應時間呈正相關。
(5) 10T|15F相較於無閃動的情況，由一致性效果造成之反應時間差異的增加量與10Hz無調控的載波的增強量正相關。
本研究透過操弄不同外在閃爍刺激引起的10Hz能量變化及其對應的行為變化，並與未受調控的情況比較。從6 Hz 和15 Hz 組合所引發的不同結果，推斷因為不同頻率的SSVEP經由不同腦區產生，α波在視覺注意力所扮演的抑制作用可能受到頻率組合的影響。本實驗中在15 Hz組合（10T|15F對比15T|10F）看到10Hz SSVEP受注意力顯著的調控，也就是局部空間的10Hz SSVEP 調控，發現對一致性效果造成影響；相反的，在6 Hz 組合中，則是影響不相容情況(incongruent condition)的反應時間。這些研究結果可增加外在閃爍刺激如何調控腦波的理解，並解析10Hz α波對注意力運作上的影響，以對未來視覺注意力實驗研究提供新的思路。
;Visual selective attention is an important cognitive function that assists us to prioritize the processing of surrounding stimuli with a limited capacity. The flanker task is one of the conventional paradigms for investigating visual selective attention. Previous studies have found that the electroencephalography (EEG) alpha activity in the parieto-occipital lobe plays a crucial role in both visual processing and selective attention. However, due to the lack of essential baseline conditions, the entrainment effect on behavioral indexes was only inferred from the comparison of different stimulus manipulations rather than changes from the typical flanker task performance. Therefore, to decipher the role of alpha oscillation in the selective attention task, we investigated the behavioral performance as well as the corresponding EEG indexes while the participants performed a modified Eriksen flanker task, in which the stimuli were composed of target and flankers flickering at different frequencies (i.e., 10Hz, 6Hz or 15Hz), that is 10T|15F, 15T|10F, 10T|6F and 6T|10F (the flicker frequency of target and flanker position is denoted as T and F, respectively). The typical no-flicker flanker task and 10T|10F trials were also added as one of the baselines to facilitate the interpretation of the 10 Hz entrainment effect.
The results show that:
(1) The overall RT, which is calculated as the average of congruent and incongruent RT, is significantly faster in the 15T|10F condition compared to 10T|15F, as well as 10T|10F and typical flanker conditions. Similar patterns are not found in any 6 Hz combinations.
(2) The congruency effect of the 10T|15F condition is significantly faster than both 15T|10F and typical flanker conditions, but no difference is observed for 6 Hz combinations.
(3) The attentional modulation of the 3 ~ 4 Hz AM modulating 10 Hz SSVEP response decomposed by HHSA is only observed in 15 Hz but not 6 Hz combination.
(4) The stronger the 10Hz power is, the larger the incongruent RTs of the 10T|10F, 6T|10F, and 10T|6F are.
(5) The increment of the congruency effect in 10T|15F trials from the typical flanker condition of each participant can be predicted by their enhanced 10 Hz power elicited by the flicker.
Collectively, in the current study, by depicting the direct relationship between the 10 Hz power change modulated by the external flicker and behavioral performance difference between each condition and the typical no-flicker condition, we aim to elucidate the alpha role in visual selective attention. Moreover, the distinct behavioral performance and the EEG responses in different conditions, which is probably due to the frequency-specific cortical network eliciting SSVEP responses, imply that the alpha inhibitory effect may depend on tagging frequency combinations. Specifically, 3 ~ 4 Hz AM modulating 10 Hz is significantly modulated by attention for 15 Hz combinations, suggesting spatial-specific 10 Hz entrainment, and then leads to the modulation on the congruency effect. On the contrary, for 6 Hz combinations, the incongruent RTs are modulated. The present findings thus contribute to the understanding of the interaction between flicker-induced response and intrinsic oscillation and further shed new lights on the interpretation of the entrainment effect. |
