Opposite patterns of hemisphere dominance for early auditory processing of lexical tones and consonants

Abstract

In tonal languages such as Mandarin Chinese, a lexical tone carries semantic information and is preferentially processed in the left brain hemisphere of native speakers as revealed by the functional MRI or positron emission tomography studies, which likely measure the temporally aggregated neural events including those at an attentive stage of auditory processing. Here, we demonstrate that early auditory processing of a lexical tone at a preattentive stage is actually lateralized to the right hemisphere. We frequently presented to native Mandarin Chinese speakers a meaningful auditory word with a consonant-vowel structure and infrequently varied either its lexical tone or initial consonant using an odd-ball paradigm to create a contrast resulting in a change in word meaning. The lexical tone contrast evoked a stronger preattentive response, as revealed by whole-head electric recordings of the mismatch negativity, in the right hemisphere than in the left hemisphere, whereas the consonant contrast produced an opposite pattern. Given the distinct acoustic features between a lexical tone and a consonant, this opposite lateralization pattern suggests the dependence of hemisphere dominance mainly on acoustic cues before speech input is mapped into a semantic representation in the processing stream.hemispheric specialization ͉ mismatch negativity ͉ preattentive auditory processing

Processing of Acoustic and Phonological Information of Lexical Tones in Mandarin Chinese Revealed by Mismatch Negativity

“…These patterns provide support for the categorical perception of tones, while at the same time evidence for the hypothesis that both hemispheres are involved in the processing of tones (Gandour, 2006), in that the processing of within-category stimuli mainly involves the acoustic processing of pitch information while the processing of across-category stimuli the phonological information. Moreover, within the time window of MMN (200-250 ms), both acoustic information and phonological information are processed in parallel, which contrasts to the two-stage hypothesis of Luo et al (2006).…”

“…MMN responses can be elicited by an oddball paradigm in which several infrequent deviant stimuli are embedded in frequent standard stimuli during auditory presentation. Luo et al (2006) found that the mean amplitude of MMN elicited by tone deviants in the right hemisphere was larger than that in the left hemisphere. Their conclusion was that at the pre-attentive stage, a stage that is characterized by automatic processing when people are unconscious about the detailed properties of the stimuli (Kubovy et al, 1999), listeners mainly process the acoustic information of lexical tones.…”

“…In particular, we relied on the MMN patterns that have been previously used successfully in this area (Luo et al, 2006;Xi et al, 2010). Previous work, including Xi et al (2010) and Zhang et al (2011), has examined only the contrast between acoustic information and phonological information as the contrast between withincategory and across-category variations.…”

“…When a native speaker processes lexical tones in Chinese, 1 the speaker deals with at least two types of information: the acoustic information that includes the physical features of auditory input such as the fundamental frequency (F0), and the phonological information that expresses lexical semantics on the basis of which word categories are identified (Luo et al, 2006;Xi et al, 2010). To investigate the difference between the processes of the acoustic vs. the phonological information in lexical tones, one line of previous research has been to understand whether lexical tonal processing in Chinese is left or right lateralized in the brain.…”

“…Luo et al (2006) used mismatch negativity (MMN) to study the features of tonal processing. MMN is a powerful method to examine the early stages of acoustic and phonological processing, as previous studies have indicated (e.g., Näätänen et al, 1978Näätänen et al, , 2007Näätänen and Alho, 1997).…”