以功能性磁振造影探討統計規律性下情緒表情處理的年齡差異

Abstract

外在環境中物體或事件的出現有其統計特性，而先前經驗會影響人類認知系統擷取這類環境中所具有的統計規律性的能力。本研究以統計規律性的角度，探討隨年齡而增加的表情感知經驗是否會影響對他人接下來表情的預測，並利用功能性磁振造影(fMRI)就生理層面探究其神經機制。實驗招募24位年輕人和24位年長者參與，在fMRI儀器內觀看四張連續且等距(0%, 10%, 20%, 30%)的臉部表情變化圖片，變化的表情可能是開心或厭惡其中一種情緒價位。實驗參與者被要求依據先導序列表情圖片變化的規律，預期接下來的表情，並在第五張圖片(目標表情)呈現時按下反應鍵判斷是否符合預期。實驗操弄了目標表情和先導序列表情的遠近程度(近或遠)以及先導圖片和目標圖片表情在情緒價位的一致性（一致或不一致）。研究假設，與年輕人相比，年長者(1)對表情會展現出更遠的預期；(2)處理正向表情會表現出正向偏好；(3)當目標圖片表情和本身預期出現遠近程度或情緒價位的衝突時，會有不同於年輕人的衝突處理反應。結果顯示在前後一致的表情序列中，年長者在厭惡表情序列展現出比年輕人更遠的預期，並在神經處理上有更多額葉區域的涉入；而在開心表情序列中，年長者則更投入於刺激本身，而大腦影像也顯現出更多基礎視知覺處理的腦區活化。當在處理不一致的表情序列時，年長者在表情程度的衝突處理與年輕人類似，顯示其能力並未隨年齡而退化，然而在處理情緒價位衝突則表現較差。根據研究結果，年長者在兩種情緒價位的表情展現出不同的擷取統計規律性能力：厭惡表情能預測較遠，但開心表情則能正確反映規律性，而年輕人則無兩情緒價位差異。本研究結果顯示表情知覺經驗的確會隨著年齡增長而影響對情緒表情的預測，並反映在大腦神經機制上。

The occurrence of objects or events in the environment comes with statistical properties, and prior experience affects the ability of the human cognitive system to capture such statistical regularity to better predict upcoming events. As perceptual experience of facial expression increases as people age, we examined the change of predictive coding in the context of emotional regularity with aging, and its neural mechanism by behavioral and functional magnetic resonance imaging (fMRI) experiments. Participants were 24 young adults (mean ± SD = 22.46 ± 2.80 years old) and 24 older adults (mean ± SD = 65.96 ± 3.74 years old) who viewed picture quartets of a sequence of facial expressions that changed in 10% intervals (i.e., 0%, 10%, 20%, 30%) from neutral to emotional (happy or disgusted) face. At the fifth frame a target facial expression was presented that was either at a near or far distance and with either congruent or incongruent valence from the last frame of the sequential expression. Participants then responded whether the target facial expression met the expectation following the sequence of changing facial expression. We hypothesized that, compared to younger adults, older adults (1) tend to make farther facial expression predictions; (2) show the positivity effect while processing positive facial expressions; (3) have different conflict processing responses if the sequence-target distance or valence of emotion violates the expectation. Results showed that with congruent emotions, older adults had a farther prediction than younger adults in a disgusted sequence, which involved more frontal areas. Older adults also focused more on happy sequence than young adults and more perception-related brain regions were activated. With incongruent emotions, older adults were worse in processing conflicts of the valence, whereas their ability to process the conflict of distance remained intact. According to our results, older adults showed different statistical regularity to facial expression in two kinds of emotional valence: They tended to predict farther on the regularity of disgusted expressions but accurately predicted happy ones, while younger adults did not show valence difference. Experience with facial expressions as people age indeed alters the predictive coding of emotional expression and reflects in the neural mechanisms of the brain.