Long-term learning in vernier acuity: effects of stimulus orientation, range and of feedback.

In hyperacuity, as in many other tasks, performance improves with practice. To better understand the underlying mechanisms, we measured thresholds of 41 inexperienced observers for the discrimination of vernier displacements. In spite of considerable inter-individual differences, mean thresholds decreased monotonically over the 10,000 stimuli presented to each observer, if stimulus orientation was constant. Generalization of learning seemed to be possible across offset-ranges, but not across orientations. Learning was slightly faster with error feedback than without it in one experiment. These results effectively constrain the range of conceivable models for learning of hyperacuity.