Asymmetric Discrimination of Pitch Contours among Non-native Tone Listeners

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A well-established perceptual bias exists in both infants and adults, favoring the shift from a less peripheral vowel to a more peripheral one. However, the perceptual processes and the information on which these processes operate are not yet fully understood. This study explored the role of frequency modulation in the development of perceptual asymmetries in speech tonal stimuli and tested the hypothesis that a shift from a less spectrally dynamic stimulus to a more spectrally dynamic one is more perceptually salient. The effects of memory load, a factor not considered by previous studies, were also explored. Fifteen native speakers of American English discriminated pairs of speech tonal stimuli varying in pitch contour (falling, rising, level) at short (250 ms) and long (1,000 ms) inter-stimulus intervals. Consistent with the spectral dynamics account, a change from a level pitch contour to a falling and a rising pitch contour was easier to detect than the opposite direction. However, inconsistent with the spectral dynamic hypothesis, a change from a falling tone was easier to discriminate than a change from a rising tone, but it resulted in a longer reaction time compared to a level tone. Poorer sensitivity to pitch contour, as opposed to pitch height or average pitch, among non-tonal language speakers may explain the results.