呈現時間對平均臉孔情緒產生左側偏誤之影響

Abstract

整體感知讓人們能夠從多個物件刺激中快速擷取出整體資訊。過去研究發現在平均多個低層次物件時（例如估計圓盤的平均大小），參與者較依賴左側刺激的訊息進行平均估計，產生左側偏誤的現象。然而，目前仍不清楚平均多個較高層次物件，如群體臉孔表情，是否也會有此現象。因此，本研究探討平均群體臉孔表情是否也存在左側偏誤，並透過三個實驗操弄不同的呈現時間（200毫秒、500毫秒和1800毫秒）對於此偏誤的影響。在每個實驗試驗中，參與者觀看螢幕上八個情緒臉孔刺激，並隨後透過調整法估計出平均群體臉孔表情。在臉孔刺激畫面中，左半邊四張臉孔以及右半邊四張臉孔的平均情緒強度可能為左側較強、右側較強、或兩側相等這三種情況。結果顯示平均臉孔表情的左側偏誤出現在500毫秒的呈現時間（實驗二），但沒有出現在呈現時間較短（200毫秒）或較長（1800毫秒）的情況。由此推測在500毫秒時平均臉孔表情產生的左側偏誤，在較充足的時間資源下，透過較細緻的個體表徵對整體估計進行修正而削弱了左側偏誤。本研究為首篇以實徵證據驗證平均群體臉孔表情也存在左側偏誤，但其效果會受到呈現時間的調節。

Ensemble perception is the process of rapidly forming summary representations of multiple items. While previous research has found that participants relied more on visual inputs from the left side of the scene and yielded a left-side bias (LSB) in the mean size estimation of discs, it is unknown whether this bias extends to the ensemble representations of higher-level features such as emotional faces. This study aimed to explore the LSB in averaging facial expressions, specifically examining its processing at varied exposure times (200 ms, 500 ms, and 1800 ms) across three experiments. Participants were asked to average the facial expressions of eight faces in each trial, with the mean emotion intensity of the face crowd on two sides (four faces on each side) manipulated to be stronger on one side or equal on both sides (left-stronger, right-stronger, and equal). Results showed that the LSB in averaging facial expressions occurred only at 500 ms exposure time, while it was absent at the shorter (200 ms) or the longer (1800 ms) exposure time. These results suggest that the development of the LSB takes time, and it is later corrected by incorporating local features of individual items during a longer exposure time of 1800 ms, thereby eliminating the LSB. This is the first study demonstrating the LSB in ensemble perception of facial expressions as a function of exposure time in such bias.