Independence of spectral contrast effects across different frequency regions in speech perceptiona)

Identification of speech sounds is influenced by spectral contrast effects (SCEs), the perceptual magnification of spectral differences between successive sounds. SCEs result in the categorization of a target sound being biased away from spectral properties in the preceding acoustic context. Given remarkable consistency in the magnitudes of these contrast effects within the same frequency region [Stilp (2019) J. Acoust. Soc. Am. 146(2), 1503-1517], it was hypothesized that they would also show stable relationships across different frequency regions. In this study, normal-hearing listeners' phoneme categorization and contrast effects were assessed where phonetic contrasts were driven by changes in low-frequency F1 ("big"-"beg" continuum), mid-frequency F3 ("dot"-"got"), or high-frequency frication spectrum regions ("sheet"-"seat"). On each trial, listeners heard a precursor sentence that was filtered to emphasize energy in the lower or higher range within one of these frequency regions, followed by a target word that hinged on the frequency region that was filtered. Results showed that SCEs influenced categorization in each frequency region, as expected. However, effect magnitudes were not correlated with each other across frequency regions within or across two participant samples. This clarifies perception-in-context on a broader scale as the influence of spectral contrast is independent across different frequency regions.