Initial performance, learning and observer variability for hyperacuity tasks.

Psychophysically-experienced and -inexperienced human observers were tested on 34 different non-stereo and 49 stereo hyperacuity stimuli. Performance reached hyperacuity levels within the first five trials for the non-stereo stimuli. For stereoacuity tasks the results were very different. Even extremely experienced observers with very low thresholds for certain stereo tasks required considerable practice to achieve their best performance for slightly different stereo tasks. Performance on both types of tasks showed considerable observer variability. These results suggest that adults do not synthesize new visual modules for hyperacuity tasks early in the visual pathway on a task-driven basis. We also interpret these results to suggest that there can be many equally general models of hyperacuity performance that show only the qualitative general trends of a "standard" observer. Incorporating individual variability might provide sufficient constraints on such models to provide clues about physiological mechanisms.