How sleep redraws phonemic categories after auditory selective adaptation.

After information has either been perceived or brought into working memory from long-term memory, it may remain active for hours or days. There is extensive evidence that sleep can consolidate newly learned material into long-term memory, and some recent work shows that sleep may also help clear out either unneeded or already established information. We examine the effect of sleep on a third type of information: adjustments to established speech categories caused by repeated exposure to a speech sound-selective adaptation. We find that sleep does not consolidate selective adaptation per se. Instead, sleep implements a change in phoneme category frequency to reflect the properties of the input-the many instances of the adapting sound that had been presented repeatedly. While adaptation temporarily reduces the perception of tokens similar to the repeating sound, sleep increases their perception, producing a "reverse adaptation" pattern. The results constrain models of phoneme category adjustment, favoring those that have separate mechanisms for assimilative versus contrastive effects over those with a single mechanism for both types of effects.