Perceptual Learning:
No Transfer Between Similar Stimuli
In The Same Retinal Position

Manfred Fahle and Michael Morgan


Abstract

Background: Recent experiments demonstrated a remarkable amount and specificity of learning simple visual tasks in humans as well as considerable plasticity of receptive fields in adult monkeys' visual cortex. We tested the specificity of improvement through learning for two almost identical stimuli in human observers.

Results: Two groups of 6 observers each were trained in two hyperacuity tasks, 3 dot bisection and 3 dot vernier discrimination. The groups started with different tasks and switched tasks after 1 hour of training. Training improved performance significantly in spite of considerable inter-observer variance, 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 obviously not based on the development of a more exact map of the individual photoreceptor positions, or by learning to fixate or accommodate the eye, but by 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 for the two similar tasks.