臺灣博碩士論文加值系統

背景：現代生活中人們無時無刻不在多樣化的環境和各式人群接觸，而我們的內在情緒和偏好影響外在行為表現。1968年Zajonc提出的單純曝光效果(Mere exposure effect)指出對個體不具任何正向獎賞意義的刺激，隨著呈現次數的增加，個體對刺激的喜歡程度也隨之上升。單純曝光效果的形成原因眾說紛紜，其中之一為重複曝光可增加個體對刺激的熟悉性，進而提升個體自身的正向情緒狀態，然而單純曝光效果形成的神經機制，至今尚未釐清。本研究旨為利用腦磁圖，探討閾下呈現單純曝光效果之動態活化表現。
資料與方法：本研究採用二因子完全受試者內設計，兩個因子分別為曝光臉孔情緒(快樂或中性)與曝光次數(重複曝光或單次曝光)。實驗分成快樂曝光、中性曝光兩部分，每部分包含重複及單次曝光兩種，每種曝光內容依序為觀看和內隱評分兩階段。觀看階段每張臉孔呈現時間為17毫秒，後面緊接出現700毫秒遮蔽(mask)圖片。觀看階段結束後為內隱評分階段，受試者依照螢幕呈現的中性圖片與形容詞「愉悅」進行符合程度的判斷。每部分最後為喜歡程度評分，受試者依據螢幕呈現的中性表情人臉進行喜歡程度的評分。實驗共招募三十三位受試者。實驗使用全頭式腦磁圖(magnetoencephalography, MEG)量測腦磁波訊號、相位鎖定因子(phase-locking factor)找出與事件相關之頻帶，以及最大對比光束構成法(maximum contrast beamformer, MCB)整合腦磁波訊號與其大腦結構影像，推估神經訊號源位置及活化強度，並對行為資料和MCB結果進行後續統計分析。
結果：相較於中性單次曝光，中性重覆曝光顯著提升受試者的正向情緒狀態，且增強左側楔前葉(precuneus; 70 ms)和減弱左側旁中央迴(paracentral gyrus; 70和100 ms)活化。此外，依據受試者內隱評分將其分為三組，相較於中性單次曝光，中性重覆曝光在高分組和低分組均減弱右側楔狀葉(cuneus; 100 ms)活化，然而左側下頂葉(inferior parietal gyrus; 100 ms)的活化分別在高分組和低分組受到減弱和增強，且僅在高分組減弱中腦(midbrain; 100, 120 和150 ms)活化。
結論：本研究發現閾下重複曝光可能經由提升熟悉感及降低生理激發、知覺負荷、注意力和警覺，誘發個體正向情緒狀態，而上述發現或許為解釋單純曝光效果之情緒理論、激發理論與知覺流暢∕歸因理論提供神經造影證據。

Introduction: Affect has been recognized as an important factor of judgment and decision making. Numerous studies have demonstrated the effect of mere exposure, repeatedly presenting a stimulus to an individual, on increasing her/his positive attitude or preference for that stimulus. One speculation of this phenomenon is that repeated exposure modulates one’s affective state toward positive through enhanced familiarity. However, the neural mechanism underlying mere exposure effect (MEE) is still unclear. This study aimed at elucidating neural correlates of formation of mere exposure effect and their temporal profile. We hypothesized that repeated exposure increases positive affect through enhancing activation of the precuneus related to familiarity and reducing activation of visual cortex because of perceptual fluency.
Methods: We conducted a subliminal experiment with a 2 (emotion; happy vs. neutral) x 2 (exposure; repeated vs. single) factorial design. Each emotion condition consisted of two exposure blocks (repeated and single) and one liking rating block. Each exposure block included one viewing stage and one implicit rating stage. During the viewing stage, subjects were presented 27 faces for 17 ms each and subsequently masked with a scrambled face image. Liking ratings for each exposed face and implicit ratings for unexposed neutral object images were measured by a four-button response pad. Thirty-three healthy volunteers were recruited in this study. Their magnetoencephalography (MEG) (Vectorview, Elekta Neuromag, Finland) were recorded and T1-weighted MRI (Siemens Medical, Erlangen, Germany) images were obtained. The MEG data were analyzed by estimating neural synchrony using phase-locking factor and spatiotemporal mapping using maximum contrast beamformer. For behavioral data, two separate two-way ANOVAs including the exposure (R/S) and facial expression (H/N) factors were performed. For neuroimaging data, paired t-test (NR vs. NS) and difference-in-difference estimate ((High group: NR-NS) vs. (Low group: NR-NS)) were performed.
Results: The behavioral results showed that repeated exposure significantly increased positive affect. The left precuneus showed increased activity and the left paracentral gyrus showed decreased activity to repeated exposure. Furthermore, we divided subjects into high and low groups based on their implicit ratings. For both groups, the right cuneus showed decreased activity to repeated exposure. The left inferior parietal gyrus showed repetition suppression in the high group, but showed repetition enhancement in the low group. Besides, only the high group had repetition suppression in the midbrain.
Conclusions: This study found that subliminal repeated exposure increased positive affect, which was associated with enhanced activation of the left precuneus and reduced activation of the left paracentral gyrus, the right cuneus, the left IPG and the midbrain. These findings suggest that possible mechanism underlying the subliminal mere exposure effect through elevated familiarity and eliminated arousal, perceptual loading, attention and alert.

Chapter 1Introduction 1
1.1 Mere exposure effect 2
1.2 Neuroimaging study 4
1.2.1 Familiarity 4
1.2.2 Repetition suppression 5
1.3 Magnetoencephalography 6
1.4 Thesis scope 7
Chapter 2 Materials and Methods 8
2.1 Subjects 9
2.2 Experimental design 10
2.3 Stimuli 11
2.4 MEG and MRI recordings 11
2.5 MEG data analysis 12
2.6 Statistical analysis 13
Chapter 3 Results 14
3.1 Behavioral results 15
3.2 Neuroimaging results 16
3.2.1 Sensor-level results 16
3.2.2 Source-level results 18
Chapter 4 Discussion 46
Chapter 5 Conclusions 49
References 51

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