The impact of tone systems on the categorical perception of lexical tones: An event-related potentials study

Abstract

This study investigates the categorical perception (CP) of pitch contours (level and rising) by native listeners of two tone languages, Mandarin and Cantonese, for both speech and nonspeech. Language background was found to modulate participants’ behavioural and electrophysiological responses to stimuli presented in an active oddball paradigm, comprising a standard and two equally spaced deviants (within- and across-category). The stimuli were divided into two sets according to the results of a two-alternative forced-choice identification test: a rising set, using a standard that listeners identified as high rising tone, and a level set, using a standard that listeners identified as high level tone. For the rising set, both groups of listeners exhibited CP in terms of their behavioural response. However, only Cantonese listeners exhibited a significant CP effect in terms of P300 amplitude. For the level set, the behavioural data revealed a shift in category boundary due, in part, to the range–frequency effect. According to the d′ scores, the CP effect elicited from Mandarin listeners was greater for nonspeech stimuli than for speech, suggesting the presence of apsychophysical boundary. There was no such behavioural contrast for Cantonese listeners. However, Cantonese listeners exhibited a significant CP effect in P300 amplitude that was influenced by the range–frequency effect, as well as a possible secondary phonological boundary. P300 amplitude is believed to index the ease of discrimination of speech stimuli by phonological information. We conclude that Cantonese listeners engaged phonological processing in order to discriminate speech stimuli more efficiently than Mandarin listeners. These findings may be due to the different tonal inventories of Mandarin and Cantonese, with Cantonese listeners required to make finer distinctions in perception of pitch height and slope than Mandarin listeners in order to discriminate the denser tone system of Cantonese.

Keywords:

• Categorical perception
• Lexical tone
• Chinese Mandarin
• Cantonese
• Event-related potentials
• P300
• Oddball paradigm

Acknowledgements

The work described in this paper was partially supported by research grants awarded to William S-Y. Wang by the Shun Hing Institute of Advanced Engineering of The Chinese University of Hong Kong (Project No. BME-8115020) and by the Research Grants Council of the Hong Kong Special Administrative Region, China.

Notes

¹Mandarin also has a neutral tone, but this tone does not provide lexical contrast.

²Cantonese also has three entering tones on syllables with stop endings. The entering tones, referred to as Tones 7, 8, and 9, have similar pitch contours to Tones 1, 3, and 6, respectively, but have shorter duration.

³In a follow-up test, five Mandarin listeners and three Cantonese listeners were instructed to rate the naturalness of the speech stimuli on a 5-point scale, ‘1’ indicating least natural, ‘5’ indicating most natural. The Mandarin listeners rated the stimuli to have naturalness 3.89±0.27 (mean±standard error); the Cantonese listeners rated the stimuli to have similar naturalness, 3.90±0.35.

⁴Two groups (10 subjects per group) of Mandarin speakers participated in a follow-up experiment. One group was instructed to identify stimuli within the rising set (stimuli #1–#7) while the second group was instructed to identify stimuli within the level set (stimuli #4–#10). The categorical boundary for the rising set was observed to lie between #4 and #5 for both speech and nonspeech, while the boundary for the level set lay between #7 and #8 for speech, confirming the presence of a range–frequency effect—for nonspeech, the position of the boundary was slightly higher at stimulus #8.

⁵We will continue to use the terms across-category and within-category to refer to the category memberships obtained from participants during the forced-choice identification test described in Procedure irrespective of changes in category boundary position due to the range–frequency or other effects.