A trained perceptual bias that lasts for weeks.

Classical (Pavlovian) conditioning procedures can be used to bias the appearance of physical stimuli. Under natural conditions this form of perceptual learning could cause perception to become more accurate by changing prior belief to be in accord with what is statistically likely. However, for learning to be of functional significance, it must last until similar stimuli are encountered again. Here, we used the apparent rotation direction of a revolving wire frame (Necker) cube to test whether a learned perceptual bias is long lasting. Apparent rotation direction was trained to have a different bias at two different retinal locations by interleaving the presentation of ambiguous cubes with presentation of cubes that were disambiguated by disparity and occlusion cues. Four groups of eight subjects were subsequently tested either 1, 7, 14, or 28 days after initial training, respectively, using a counter-conditioning procedure. All four groups showed incomplete re-learning of the reversed contingency relationship during their second session. One group repeated the counter-conditioning and showed an increase in the reverse bias, showing that the first counter-conditioning session also had a long-lasting effect. The fact that the original learning was still evident four weeks after the initial training is consistent with the operation of a mechanism that ordinarily would improve the accuracy and efficiency of perception.