Tilt aftereffect from orientation discrimination learning.

Using psychophysical methods, the present study aims to investigate whether orientation discrimination learning can modify the visual cortex and how the modification is related to the development of perceptual learning (performance improvement). In Experiment 1, subjects were trained with an orientation discrimination task at the orientation of 15° right tilted from the vertical. The training not only improved subjects' orientation discrimination performance, but also shifted their perceived vertical toward the trained orientation, which resembles a well-known visual illusion-tilt aftereffect. Interestingly, the change of perceived vertical and performance improvement had different dynamics. Subjects' performance levels were maintained at a constant level, even 2 months after training. However, their perceived vertical changes reduced dramatically 1 week after training. In addition, Experiment 1 showed that there was only a weak transfer of the perceived vertical change from the trained location to the untrained location. Experiment 2 demonstrated that subjects' perceived vertical was not affected by training at 75°. These results suggest that the orientation discrimination training could modify neuronal responses in human retinotopic visual areas and the development of perceptual learning is not a single neural process.