角广泛存在于自然界中，在正式学习之前往往已经被人们注意和熟悉。在在数学家的严格定义中，直角、锐角和钝角共同构成劣角的三种类别。锐角、钝角均包含连续角度范围构成的的一组角，但直角仅包含90°一个角度，因此直角是一种特殊的类别。在角的概念层级中，直角所处的地位是一个核心问题。本研究通过知觉和概念的两个偏离觉察范式，探究劣角是否存在类别知觉和成人心中的劣角概念层级，关注在知觉和概念层面直角的特殊性是否存在。

保证除角度外其他维度不变，实验一探究被试对于不同类别角度中角度变化的敏感性；实验二探究被试在直角、锐角和钝角同时呈现时是否会将直角看作特殊的类别。研究结果表明：（1）直角（90°角）不仅是锐角、直角、钝角概念分类的分界线，也是劣角三种类别知觉分类的分界线；（2）人们将直角看作特殊的类别。在劣角的概念结构中，直角、锐角、钝角是同一层级的三种概念类别。

Angles are widely found in our life. Before learning them in school, we are very familiar with angles. In the strict definition of Euclidean geometry, minor angles are divided into right angles, acute angles and obtuse angles. Both acute and obtuse angles contain a continuous range of angles, but right angles only contain 90°, so right angle is a special category. In the conceptual hierarchy of angles, the position of the right angle is a core problem. This study wants to explore whether there is a category perception of minor angles, and to find the angle concept hierarchy in adult.

Experiment 1 tests the sensitivity of angle changing in different angle categories. Experiment 2 explores whether subjects regard right angles as special categories when different kind of minor angles are presented at the same time. The results show that : (1) Right angles (90 degrees) are not only the perceptual boundary between the two categories, but also the dividing line of right angles, acute angles and obtuse angles. (2) People regard right angles as special categories. Acute angles, obtuse angles and right angles are at the same hierarchy.