上重偏好不再：嬰兒的早期臉孔與種族專化歷程

No More Top-Heavy Bias: On Early Specialization Process for Face and Race in Infants

本文主要目的在回顧嬰兒對於臉孔和種族的知覺發展的早期專化歷程。我們首先回顧探討新生兒臉孔偏好的幾篇經典研究，接著進一步介紹解釋此臉孔偏好的三大理論取向，包括八零年代的「線性模式取向的感官假說」、九零年代的嬰兒對「特定臉孔表徵的先天性偏好理論」，以及近十年內Turati等人主張的「非特定的知覺偏好理論」。本文的第三部分深入討論Turati等人的「上重偏好假說」的一些限制與相關的後續研究，利用強迫選擇新奇偏好注視法和眼動追蹤儀，我們重新檢驗此假說並發現二、三個月大的嬰兒並未顯現出上重偏好；表示此非特定的上重結構的偏好可能只是個很短暫的趨力，當嬰兒開始累積視覺經驗，他們會轉而傾向去注意到真正的臉孔表徵。本文的第四大段闡述生命早期的臉孔學習與專化歷程，除了回顧來自於神經生理方面的支持證據外，也探討嬰兒對於臉孔的種族訊息的敏感度如「他種族效應」的研究。「他種族效應」的研究結果發現，三個月大的嬰兒較偏好自己種族的臉孔，而我們研究台灣地區四到九個月大的嬰兒辨識不同種族臉孔的能力，發現嬰兒且辨識自己種族臉孔的能力會最早出現，且會隨著年齡增長而有所精進；而辨認他種族的能力會較晚出現且進步有限。整體而言，綜觀我們所回顧的西方文獻與本土的研究，本論文支持早期臉孔知覺發展與專化的「經驗─期待」觀點。

Neonates display reliable visual preferences for human faces and face-like stimuli, which has been taken as strong evidence for an innate domain-specific bias toward faces. Alternatively, neonatal face preference can be explained by an innate non-specific top-heavy configuration bias on the basis that faces are inherently top-heavy. This review article aims to address the early specialization process for face and race in Taiwanese infants based our recent work. In the first two sections, we will review the classic findings on the neonatal face preference research. Three broad theories, the sensory hypothesis by linear system approach in the late 80s, the innate domain-specific representation hypothesis in the early 90s, and the non-specific top-heavy bias hypothesis in the last decade, will be addressed and compared. In the third section, we further explored some deeper issues regarding the top-heavy configuration bias hypothesis as well as our recent follow-up work. Using a forced-choice novelty preference method, we found that 2.5- to 4.5-month-old infants showed significant and equal novelty preferences, suggesting a reliable discriminability between the two configurations and a disappearance of the top-heavy bias. Moreover, using an eye-tracker, we investigated whether the top-heavy bias is still present in 3- to 5.5-month olds and in adults as a comparison group, and found no evidence for the top-heavy bias in both infants and adults. In the forth section, we illustrated the idea of an early specialization process for human face and race. Several recent developmental cognitive neuroscience studies on the infant brain as well as the behavioral studies on the other-race-effect in Caucasian and Taiwanese infants were reviewed. Taken together, our position on early face processing is in line with experience-expectant view; this view considers the brain specialization as emerging gradually from the interaction between small innate constraints and the critical input provided by the species-typical or race-typical environment.