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.