Effects of cognitive load on the categorical perception of Mandarin tones

Purpose: This study investigated the effect of cognitive load (CL) on the categorical perception (CP) of Mandarin lexical tones to discuss the application of the generalized pulse-skipping hypothesis. This hypothesis assumes that listeners might miss/skip temporal pulses and lose essential speech information due to CL, which consequently affects both the temporal and spectral dimensions of speech perception. Should CL decrease listeners’ pitch sensitivity and impair the distinction of tone categories, this study would support the generalized pulse-skipping hypothesis.
Method: Twenty-four native Mandarin-speaking listeners were recruited to complete a dual-task experiment where they were required to identify or discriminate tone stimuli while concurrently memorizing six Chinese characters or graphic symbols. A no-load condition without a memory recall task was also included as a baseline condition. The position of categorical boundary, identification slope, between-/within-category discrimination, and discrimination peakedness were compared across the three conditions to measure the impact of CL on tone perception. The recall accuracy of Chinese characters and graphic symbols was used to assess the difficulty of memory recall.
Results: Compared to the no-load condition, both load conditions showed a boundary shift to Tone 3, shallower identification slope, poorer between-category discrimination, and lower discrimination peakedness. Within-category discrimination was negatively affected by CL in the graphic symbol condition only, not in the Chinese character condition.
Conclusions: CL degraded listeners’ sensitivity to subtle F0 changes and impaired CP of Mandarin lexical tones. This provides support for the generalized pulse-skipping hypothesis. Besides, the involvement of lexical information modulated the effect of CL.