Orientation specificity of learning vernier discriminations

Orientation selective neurons in the primary visual cortex typically respond to a range of orientations that covers 20° or more, while in psychophysical experiments, orientation bandwidth is often clearly narrower. Here, we measure the orientation specificity of perceptual learning for vernier discriminations. More than 70 observers, in separate groups, practiced a vernier discrimination task with a constant stimulus orientation. After a 1 h session of training, the vernier was rotated by 2°, 4°, 10°, 20°, 45° or 90°. Improvement through training in the first session transferred to the second session (tested on the next day) up to 10° of stimulus rotation. We found no transfer for rotations of 20°, 45° and 90° Hence, the orientation half-bandwidth of perceptual learning is around 15°, leading to a bandwidth of 30° and corresponding to that of single neurons in early visual cortices, while being narrower than that in higher cortical areas.