Modulatory Effect of Emotional Facial Expression on Inhibitory Control Revealed by Pinch-Force Measures and Electrophysiological Indices

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Title:	Modulatory Effect of Emotional Facial Expression on Inhibitory Control Revealed by Pinch-Force Measures and Electrophysiological Indices
Authors:	林靜儀;Lam, Cheng-I
Contributors:	認知與神經科學研究所
Keywords:	情緒;抑制衝動;停止信號作業;事件相關電位;Emotion;Inhibitory Control;Stop Signal Task;N1;Event-related Mode
Date:	2019-01-09
Issue Date:	2019-04-02 15:08:38 (UTC+8)
Publisher:	國立中央大學
Abstract:	背景﹕情緒臉部表情在我們日常溝通中扮演重要的角色，根據趨向與避免動機理論，正面情緒與趨向動機相關而負面情緒與避免動機相關。相比中性情緒的臉部表情，正面情緒的臉部表情在抑制衝動能力的難度比較高。以前研究大多利用Go Nogo作業探討不同情緒向性的臉部表情與抑制衝動能力的關係，但是，很少研究利用停止信號作業探討不同情緒向性的臉部表情怎樣影響我們的抑制衝動能力。停止信號作業的其中一個優點是它提供抑制反應時間 (SSRT) 與抑制功能 (Inhibition Function)的測量，從而對抑制衝動過程的時間性有更清楚的了解。Pessoa與其團體運動停止信號作業，並利用不同臉部表情的人臉當作停止信號 (中性、開心及害怕)，探討臉部表情怎樣調節抑制衝動能，他們發現當開心及害怕的臉當作停止號時，受試者的SSRT比中性情緒的人臉短，但開心與害怕的臉之間的SSRT並沒有顯著的差異，由於在先前研究中，不同臉部表情的人臉混合在實驗裡，受試者可能在任何人臉出現時抑制他們的反應，而並沒有真正關注臉部表情的差異。此研究目的探討臉部表情如果影響我們的抑制衝動能力，並考慮到現實生活中的選擇性，因此利用刺激選擇性停止信號作業為主要實驗作業。在過去的研究中，事件相關電位的N2及P3認為是探討抑制衝動能力的主要成份，但是，除了抑制衝動能力之外，N2也被提到跟衝突檢測有關，因此N2的角色是模糊的。另一方面，SSRT的時間大約為200毫秒，而P3出現的時間太晚並無法解釋抑制衝動能力的過程。因此，有研究提出早期的事件相關電位成份例如N1能更好地反映抑制過程。此研究目的旨在區分N1及N2在運動抑制中的作用，除了基本停止條件外，作業中加上一個繼續條件，繼續信號與停止信號具有相似注意特徵，但在繼續條件中，受試者需要忽略信號並繼續他們的動作。透過比較成功停止條件 (SST)、不成功停止條件 (USST)以及繼續條件 (Cont. Go)，N1及N2在抑制衝動過程的角色能被澄清。方法﹕我們量測了30名受試者的腦電波，為了探討情緒臉部表情跟動作抑制能力之間的關係，此實驗操縱兩個實驗條件探討其關係﹕1) 害怕人臉用作停止信號以及開心人臉用作繼續信號，當害怕人臉出現時，受試者需要抑制他們的動作，而當開心人臉出現時，受試者需要忽略信號並繼續他們的動作。2) 開心人臉用作停止信號而害怕人臉作用繼續信號。除此之外，目前的作業通過以下兩種方法進行了修改﹕1) 透過採用固定停止信號延遲 (SSD) 方法代替樓梯追蹤方法，探討不同情緒向性跟抑制衝動過程之間的時間關係。2) 採用指握力器代替傳統鍵盤按鍵，我們認為與傳統鍵盤按鍵相比，力度測量可以為提供抑制衝動過程提供更多的資訊。結果﹕腦電波結果顯示成功停止條件引起的N1波幅比不成功停止條件的N1波幅大，但在成功停止條件及繼續條件之間並沒有顯著的差異。這結果表示N1成份不僅代表停止信號及繼續信號的辨別，更在抑制過程扮演重要的角色。此外，不成功停止條件跟繼續條件的N2 波幅並沒有顯著的差異，而在繼續條件及不成功停止條件中，N2波幅隨著信號延遲增加，推論出比起抑制過程，N2成份反映衝突檢測。另一方面，在比較臉部表情對抑制衝動能力之影響，行為結果顯示不同之臉部表情對抑制功能產生差異，在早期的停止信號延遲時，開心人臉是停止信號的錯誤率比害怕人臉停止信號的錯誤率高，在中期及後期的停止信號延遲，兩者之間的錯誤率並沒有顯著的差異。腦電波結果並顯示害怕人臉的N1波幅比開心人臉的N1波幅大。力度測量顯示，害怕人臉及開心人臉之間的力度並沒有顯著的差異。結論﹕總括而言，此研究提供了證據支持N1在抑制控制中的重要角色，比起分辨信號，N1更可能反映抑制控制的過程，另外，N2更可能反映衝突檢測。行為結果與腦電波結果支持正向情緒的臉部表情跟趨向動機相關，並比負向情緒更難被抑制的假設，除此之外，情緒影響在運動執行過程的早期階段更為顯著。力度測量結果顯示，不同情緒向性的臉部表情在動作力度之間並沒有顯著的差異，証明了情緒效應對抑制能力的調節主要發生在腦部。總而言之，目前研究提供了証據區分N1跟N2在抑制衝動扮演的角色，不同情緒向性的臉部表情影響我們的抑制衝動能力，而情緒效應在運動執行過程的早期階段更為顯著。 ;Background: Emotional facial expression plays an important role in our social interaction and communication. According to the approach and avoidance motivation, negative emotions have been generally thought to be avoidance oriented and positive emotions to be approach oriented. Facial expression in positive valence is related to approach behavior and is more difficult to inhibit than responses to neutral faces. Prior go/nogo studies found that perceived facial expression in different emotional valences could modulate motor inhibition. Intriguingly, little studies focus on how perceived emotional facial expression in difference valences modulate our motor inhibition by adopting stop signal task. Since stop signal task provides measurement of SSRT and inhibition function, the advantage of the task is that the time course of inhibition process can be assessed. Pessoa and colleagues investigated how perceived emotional facial expression modulates inhibitory control by utilizing emotional faces (i.e. fearful, happy and neutral faces) as stop signals in stop signal task. SSRT found to be shorter for emotional faces than neutral faces. No difference in SSRT between fearful and happy face proposed that emotional faces enhanced inhibitory control but there is no modulatory effect of emotional valence in inhibition. The limitation of prior study is that participants might inhibit their responses only when faces appeared without concerning the facial expressions. Current study aims to elucidate how perceived facial expression modulate motor inhibition by utilizing stimulus-selective stop signal task, because it addresses the selectivity and is more representative of real life situation. Previously, electrophysiological N2 and P3 component were proposed as important components in inhibition in some studies. However, the role of N2 is ambiguous as it is reported to be involved in conflict detection. Because SSRT is around 200 ms, the appearance of P3 is too late to account for the inhibition process. It was proposed that early component like N1 may better reflect the inhibition process. Current study aims to differentiate the role of N1 and N2 component in motor inhibition by utilizing additional continue go trials that share similar attentional characteristics with stop trials, but participants are required to respond. We argue that the role of N1 and N2 can be clarified by comparing successfully stopped trials (SST), unsuccessfully stopped trials (USST) and continue go trials (Cont. Go). Method: Thirty participants were recruited from National Central University in this study. Stimulus-selective stop signal task with electroencephalography (EEG) measurement was employed. In order to investigate the relationship between emotional facial expression and motor inhibition, two experimental conditions were manipulated to investigate the relationships: 1) Fearful Face adopted as stop signal that the subjects are required to inhibit their pre-potent action while happy face adopted as Continue Go signal that the subjects have to ignore it and continue with their action. (i.e. Fearful Stop and Happy Continue Go Condition) 2) Happy face was adopted as stop signal and happy face adopted as Continue Go signal (i.e. Happy Stop and Fearful Continue Go Condition). Moreover, the current paradigm was modified in two following ways: 1) Fixed SSD method was utilized instead of the staircase tracking method. In this way, the non-cancelled rate can be plotted in the function of stop signal delays (SSDs) and the effect of emotional valences on the time course of the inhibition process can be elucidated. 2) Force pincher was used instead of traditional key pressing. In light of this, the peripheral stage and graded nature of inhibition process can be characterized by force measurement, we think that, compared to traditional key pressing, force pincher can provide more measures for the investigation of motor inhibition process. Results: Larger N1 amplitudes were observed in successfully stopped trials (SST) than in unsuccessfully stopped trials (USST) but no difference between successfully stopped trials (SST) and continue go trials (Cont. Go). This pattern of results suggests that N1 component may not only represent the discrimination between the stop and continue go signals, but also the inhibition process due to the overlapping and successful inhibitory processes in SST and Cont. Go trials. No difference found in N2 amplitude between USST and Cont. Go trials. The N2 amplitude increased along with stop signal delays (SSDs) in both USST and Cont. Go trials, inferring that N2 is likely to reflect conflict detection rather than the inhibition process. In a comparison of emotional facial expression in motor inhibition, the behavioral result shows that there is a significant difference in the inhibition function to stop signals in different emotional valences. When the happy face was used as a stop signal, the non-cancelled rate was higher than that of the fearful face in early SSD but there was no difference in middle and late SSDs. For the electrophysiological result, larger N1 amplitude elicited by fearful face than happy face in SST. In the comparison of force measurement, no difference in force measurement between emotional valences in USST. Peak force rate to happy face was larger than that of the fearful face in early stop signal delay in continue go response. Conclusion: In sum, current study provides evidence supporting the important role of the N1 component in inhibitory control. Compared to discrimination, N1 component is more likely to account for inhibition process. On the other hand, N2 is proposed to reflect conflict detection rather than inhibitory control. The lower non-cancelled rate in early SSD and larger N1 amplitude to fearful face than happy face in SST supports the idea that facial expression in positive valence is related to approach motivation, and is more difficult to be inhibited than negative valence. The effect of emotional valence is more robust at an early stage of the motor execution process. As revealed by force measurement results, no difference in peak force and peak force rate between emotional facial expressions in unsuccessfully stopped response suggesting that the modulatory effect of emotional valence on inhibition to be more robust in the central stage than in the peripheral stage of motor inhibition process. Furthermore, larger peak force rate was observed to be larger to happy face than to fearful face in early SSD in continue go response, inferring that the happy face results in higher efficiency to reinitiate the go response due to the sudden signal and the effect of emotional valence is more robust in the early stage of motor response. Taking together, the current study provides evidence to differentiate the role of N1 and N2 component in inhibitory control. From the combination of electrophysiological and peripheral pinch-force measurement, it is concluded that motor inhibition can be modulated by emotional facial expression in different valences. Moreover, emotional facial expression modulates our motor inhibition in the early stage of motor response and the modulatory effect is more robust in the central level rather than peripheral level along the motor inhibition process.
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