Sleep does not consolidate selective adaptation per se but instead implements a change in phoneme category frequency to reflect the properties of the input, producing a 'reverse adaptation' pattern.
Key Findings
Results
Sleep produces a 'reverse adaptation' effect on phonemic categories rather than consolidating selective adaptation.
While auditory selective adaptation temporarily reduces perception of tokens similar to a repeating sound, sleep subsequently increases their perception.
This pattern is described as 'reverse adaptation' — the opposite of the original adaptation effect.
The finding indicates sleep does not simply strengthen or maintain the adapted state but instead shifts perception in the contrastive direction.
Results
Sleep implements a change in phoneme category frequency to reflect the statistical properties of the auditory input during adaptation.
The repeated exposure to an adapting sound (many instances) during selective adaptation is interpreted by the sleeping brain as evidence about the frequency of that phoneme in the environment.
Rather than consolidating the perceptual suppression caused by adaptation, sleep adjusts category boundaries to reflect the high frequency of the adapting token.
This assimilative shift (increasing perception of sounds similar to the adapting token) is distinct from the contrastive suppression seen during waking adaptation.
Discussion
The results favor models of phoneme category adjustment that have separate mechanisms for assimilative versus contrastive effects.
Models with a single mechanism for both assimilative and contrastive effects are not supported by these findings.
The dissociation between waking selective adaptation (contrastive) and post-sleep change (assimilative) requires at least two distinct processes.
The authors state 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.'
Background
Sleep can affect a third type of information beyond consolidation of newly learned material and clearing of unneeded information: adjustments to established speech categories.
Prior research established sleep's role in consolidating newly learned material into long-term memory and in clearing out unneeded or already-established information.
This study identifies a distinct role: modulating temporary adjustments to pre-existing, established phonemic categories.
Selective adaptation represents a transient perceptual shift in an established category, not new learning, making its interaction with sleep theoretically distinct.
Background
Adapted speech information can remain active and be processed during sleep hours after initial exposure.
The authors note that after information has been perceived or brought into working memory, 'it may remain active for hours or days.'
Sleep-dependent processing acts on the memory trace of the adaptation experience, not just on the original long-term category representation.
This suggests sleep has access to relatively recent perceptual experiences involving established categories, not only explicit newly learned content.
What This Means
This research suggests that sleep plays a surprising role in reshaping how we perceive speech sounds. The study examined a well-known phenomenon called 'selective adaptation,' where hearing the same speech sound repeatedly (like the sound 'b') makes you temporarily less likely to identify similar sounds as belonging to that category — a kind of sensory fatigue. The key question was what happens to this temporary perceptual shift after a period of sleep. Rather than simply preserving or strengthening the adaptation effect, sleep actually reversed it: after sleeping, participants became more likely to perceive sounds as belonging to the frequently heard category, the opposite of what adaptation produces while awake.
The researchers interpret this reversal as sleep essentially 'updating' the brain's internal tally of how common different speech sounds are. When a person hears a particular sound dozens of times during an adaptation experiment, sleep appears to treat that repeated exposure as meaningful statistical information — evidence that this sound is frequent in the environment — and adjusts the brain's phoneme category accordingly. This is an assimilative effect (pulling perception toward the repeated sound), while waking adaptation is a contrastive effect (pushing perception away from it), and the two appear to be driven by separate mechanisms in the brain.
These findings matter because they reveal that sleep does more than just consolidate new memories or clear out old ones — it can also reshape well-established perceptual categories based on recent experience. This has implications for understanding how the brain maintains and updates its representations of language sounds over time, and suggests that models of speech perception need to account for at least two distinct processes: one for the immediate, contrastive effects of sensory repetition, and another for the longer-term, assimilative adjustments that occur during sleep.
Dumay N, Samuel A. (2026). How sleep redraws phonemic categories after auditory selective adaptation.. Psychonomic bulletin & review. https://doi.org/10.3758/s13423-025-02819-x