Patients with metamorphopsia perceive objects or faces as being distorted and/or different in size. In most cases, recognition is not impaired. The stimulus specificity, particularly in the case of face perception, has led to the suggestion that metamorphopsia is a deficit at the entry level of category-specific recognition systems; in this case, the face processing system. An explanation in terms of a visuosensory deficit (i.e., Funktionswandel) that affects the perception of specific stimulus categories has not been systematically evaluated. In this study, we report two patients (MZ and CM) who experienced hemi-metamorphopsia for faces after a stroke in the posterior part of the brain. Despite the distortions, they could still match and recognize faces. We carried out a detailed evaluation of their visual-sensory status and found that both MZ and CM had specific problems with discriminating and estimating sizes and shapes, especially in the contralesional visual field. It was concluded that these cases, metamorphopsia was not due to a higher-order perception impairment specific for faces, but rather of a specific impairment in shape perception in the contralesional visual field that proportionally affects the perception of faces.

中文翻译：

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Funktionswandel在变态中的作用。

患有变形症的患者认为物体或面部变形和/或大小不同。在大多数情况下，识别不会受到影响。刺激的特异性，特别是在面部感知的情况下，导致人们提出，在特定类别识别系统的入门级，变态是一种缺陷。在这种情况下，是人脸处理系统。关于影响特定刺激类别感知的视觉感觉缺陷（即Funktionswandel）的解释尚未得到系统评估。在这项研究中，我们报告了两名患者（MZ和CM）在大脑后部卒中后面部出现半形变。尽管存在扭曲，但它们仍然可以匹配并识别人脸。我们对他们的视觉感觉状态进行了详细的评估，发现MZ和CM在辨别和估计尺寸和形状时都存在特定的问题，尤其是在对侧视野中。可以得出结论，这些情况，变态不是由于面部特有的高阶知觉障碍所致，而是归因于在对侧视野中按比例影响面部知觉的形状知觉中的特定障碍。