普拉德—威利症候群是一種與輕度和中度智能遲緩有關的先天性基因異常疾病。本研究以一名普拉德—威利症候群的病友(AH)為主要研究對象，旨在探查語意分類的兩個重要層面:語意類別外部的「階層結構」與語意類別內部的「原型效應」。透過兩組使用語言/非語言刺激的線上語意作業，我們發現與心理年齡相同的國小孩童相比，AH在整體的表現上落後許多。進一步的質性訪談證實AH的分類階層結構不完全，並且對於一些分類結構下的典範例子也缺乏固有的語意知識。然而，在AH較能掌握的語意類別裡，原型效應就略有示現。最後，本研究也在AH的言談中發現其的語言問題，再再驗證AH相較於正常孩童確實有概念知識上的缺損。

Prader-Will Syndrome (PWS), a multiple genetic anomaly disorder, is mainly associated with mild to moderate mental retardation. The purpose of the present study was to investigate the intactness of a PWS patient’s (AH) conceptual structure through “taxonomical hierarchy” and “prototypicality”, two vital dimensions capturing the external and internal structure of semantic categorization. Two experiments with linguistic and non-linguistic conceptual tasks revealed that the patient’s performance was much poorer than that of the mental age-matched normal controls. Further corroborated by follow-up qualitative interviews, AH’s incompleteness in her taxonomical hierarchy and deficiencies in the semantic representations were demonstrated for some exemplars under certain categories. However, prototypicality in AH was manifest to a certain degree in categories which AH had better knowledge of. Other linguistic impairment not directly related to hierarchy and prototypicality was also observed, evidencing the incompleteness of her conceptual knowledge as opposed to that of normal controls.