Figure 1.

Stimuli and procedures in Experiment 1. A. Procedures of the whole experiment. B. Orientations and category. The arrow points to the orientation as the category boundary, which was randomly selected from 42.5° 87.5° 132.5° and 177.5° clockwise from the vertical for each subject. The orientations in the red zone belonged to Category 1 and those in the blue zone belonged to Category 2. C. The procedure of each trial in the category training. D. Three orientations used in the VPL pre- and posttest stages, the trained orientation, an untrained orientation belonging to the same category as the trained orientation (same category orientation) and the other untrained orientation belonging to the other category (different category orientation). The angular difference between the trained orientation and the same category orientation was equal to that between the trained and the different category orientation. E. The procedure of each trial in the orientation detection task. See also Figure S1.