Abstract
Learning to associate written letters/characters with speech sounds is crucial for reading acquisition. Most previous studies have focused on audiovisual integration in alphabetic languages. Less is known about logographic languages such as Chinese characters, which map onto mostly syllable-based morphemes in the spoken language. Here we investigated how long-term exposure to native language affects the underlying neural mechanisms of audiovisual integration in a logographic language using magnetoencephalography (MEG). MEG sensor and source data from 12 adult native Chinese speakers and a control group of 13 adult Finnish speakers were analyzed for audiovisual suppression (bimodal responses vs. sum of unimodal responses) and congruency (bimodal incongruent responses vs. bimodal congruent responses) effects. The suppressive integration effect was found in the left angular and supramarginal gyri (205–365 ms), left inferior frontal and left temporal cortices (575–800 ms) in the Chinese group. The Finnish group showed a distinct suppression effect only in the right parietal and occipital cortices at a relatively early time window (285–460 ms). The congruency effect was only observed in the Chinese group in left inferior frontal and superior temporal cortex in a late time window (about 500–800 ms) probably related to modulatory feedback from multi-sensory regions and semantic processing. The audiovisual integration in a logographic language showed a clear resemblance to that in alphabetic languages in the left superior temporal cortex, but with activation specific to the logographic stimuli observed in the left inferior frontal cortex. The current MEG study indicated that learning of logographic languages has a large impact on the audiovisual integration of written characters with some distinct features compared to previous results on alphabetic languages.
Highlights
Learning to read involves the integration of multisensory information and combining it with meaning
We presented Chinese characters and speech sounds as stimuli in A, V, audiovisual congruent (AVC), and audiovisual incongruent (AVI) conditions to native speakers of Chinese and used native speakers of Finnish, who were naive to Chinese, as a control group to verify the effects of long-term exposure to these stimuli
Our findings demonstrated the effect of long-term exposure to logographic language on audiovisual integration processes for written characters and speech sounds
Summary
Learning to read involves the integration of multisensory information (primarily from the auditory and visual modalities) and combining it with meaning. The ability to read is not hard-wired in the human brain through the evolution since written language is a recent cultural invention which has only existed for a few thousand years (Liberman, 1992). It takes years of repetition and practice to form the long-term memory representations of audiovisual language objects, which would enable fluent readers to successfully automatize the integration of language-related auditory and visual sensory information (Froyen et al, 2009). Understanding of such character-speech integration in logographic languages may provide more insights into the universal and language-specific brain circuits underlying audiovisual integration in reading acquisition
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