Background: Recent experiments have demonstrated a remarkable amount of specificity in the learning of simple visual tasks in humans, as well as considerable plasticity of receptive fields in the visual cortex of adult monkeys. Here, we tested the specificity of improvement through learning in the performance of human observers on two tasks using almost identical stimuli.
Results: Two groups, of six observers each, were trained in two hyperacuity tasks - three-dot bisection and three-dot vernier discrimination. The groups started with different tasks, and switched tasks after one hour of training. Training improved performance significantly, in spite of considerable variability between observers, but improvement did not generalize from one of these tasks to the other. This result indicates that perceptual learning can be extremely stimulus specific, and that deviations from the same standard but in orthogonal directions require completely new training.
Conclusions: Learning is not based on the development of a more exact map of positional information, or on training to fixate or accommodate the eye, but on a better discrimination between the stimuli using one specific stimulus dimension. We also demonstrate that observers differ considerably, not only in their speed of learning, but also in their relative level of performance on the two similar tasks.