2000 年 7 巻 4 号 p. 275-291
Two experiments are reported examining how identity and orientation are perceived and employed for the purpose of orientation-invariant shape recognition. In Experiment 1, observers judged the degree of similarities between two-dimensional line patterns. There were three experimental conditions: shape-variable, transformation-variable, and shape-and-transformation-variable. Comparisons among the derived configuration of each condition revealed that shape and transformation are represented independently as separate perceptual similarity subspaces. Whereas shape refers to the categorical spatial relations of distinctive features necessary for identification, orientation, or transformation, is estimated from the absolute location of the orientation-informative feature within a perceived shape. Generally, such orientation-informative features are defined by structural properties. In Experiment 2, using a yes-no recognition memory task, it was shown that observers were more sensitive to the structural properties of the rotated line patterns compared to the upright line patterns. This indicated that orientation-transformation information that was perceived independently of shape-identity information biased the establishment of the canonical, or upright, form of the rotated pattern. The results of these two experiments suggested that the recognition system efficiently decomposed the perceived shape of an object into identity and orientation at the perceptual stage of recognition for the purpose of achieving orientation-invariance. The relation with recent findings in neuroscience is also discussed.