Continuous dynamics in behavior reveal perceptual nonlinearities aid speech categorization in noise

Spoken language comprehension requires listeners map continuous features of the speech signal to discrete category labels. Categories are however malleable to surrounding context; listeners’ percept can dynamically shift depending on the sequencing of adjacent stimuli resulting in a warping of the heard phonetic category (i.e., hysteresis). Here, we investigated whether such perceptual nonlinearities—which amplify categorical hearing—might further aid speech processing in noise-degraded listening scenarios. We measured continuous dynamics in perception and category judgments of an acoustic-phonetic vowel gradient via mouse tracking. Tokens were presented in serial vs. random orders to induce more/less perceptual warping while listeners categorized continua in clean and noise conditions. Listeners’ responses were faster and their mouse trajectories closer to the ultimate behavioral selection (marked visually on the screen) in serial vs. random order, suggesting increased perceptual attraction to category exemplars. Interestingly, order effects emerged earlier and persisted later in the trial time course when categorizing speech in noise. These data describe a new functional benefit of perceptual nonlinearities to speech perception yet undocumented: warping strengthens the behavioral attraction to relevant speech categories while simultaneously assisting perception in degraded acoustic environments.