Sound symbolism processing is lateralized to the right temporal region in the prelinguistic infant brain.

Sound symbolism, which is the systematic and non-arbitrary link between a word and its meaning, has been suggested to bootstrap language acquisition in infants. However, it is unclear how sound symbolism is processed in the infants' brain. To address this issue, we investigated the cortical response in 11-month-old infants in relation to sound-symbolic correspondences using near-infrared spectroscopy (NIRS). Two types of stimuli were presented: a novel visual stimulus (e.g., a round shape) followed by a novel auditory stimulus that either sound-symbolically matched (moma) or mismatched (kipi) the shape. We found a significant hemodynamic increase in the right temporal area, when the sound and the referent sound were symbolically matched, but this effect was limited to the moma stimulus. The anatomical locus corresponds to the right posterior superior temporal sulcus (rSTS), which is thought to process sound symbolism in adults. These findings suggest that prelinguistic infants have the biological basis to detect cross-modal correspondences between word sounds and visual referents.

Sound symbolism scaffolds language development in preverbal infants.

A fundamental question in language development is how infants start to assign meaning to words. Here, using three Electroencephalogram (EEG)-based measures of brain activity, we establish that preverbal 11-month-old infants are sensitive to the non-arbitrary correspondences between language sounds and concepts, that is, to sound symbolism. In each trial, infant participants were presented with a visual stimulus (e.g., a round shape) followed by a novel spoken word that either sound-symbolically matched ("moma") or mismatched ("kipi") the shape. Amplitude increase in the gamma band showed perceptual integration of visual and auditory stimuli in the match condition within 300 msec of word onset. Furthermore, phase synchronization between electrodes at around 400 msec revealed intensified large-scale, left-hemispheric communication between brain regions in the mismatch condition as compared to the match condition, indicating heightened processing effort when integration was more demanding. Finally, event-related brain potentials showed an increased adult-like N400 response - an index of semantic integration difficulty - in the mismatch as compared to the match condition. Together, these findings suggest that 11-month-old infants spontaneously map auditory language onto visual experience by recruiting a cross-modal perceptual processing system and a nascent semantic network within the first year of life.

How sound symbolism is processed in the brain: a study on Japanese mimetic words.

Sound symbolism is the systematic and non-arbitrary link between word and meaning. Although a number of behavioral studies demonstrate that both children and adults are universally sensitive to sound symbolism in mimetic words, the neural mechanisms underlying this phenomenon have not yet been extensively investigated. The present study used functional magnetic resonance imaging to investigate how Japanese mimetic words are processed in the brain. In Experiment 1, we compared processing for motion mimetic words with that for non-sound symbolic motion verbs and adverbs. Mimetic words uniquely activated the right posterior superior temporal sulcus (STS). In Experiment 2, we further examined the generalizability of the findings from Experiment 1 by testing another domain: shape mimetics. Our results show that the right posterior STS was active when subjects processed both motion and shape mimetic words, thus suggesting that this area may be the primary structure for processing sound symbolism. Increased activity in the right posterior STS may also reflect how sound symbolic words function as both linguistic and non-linguistic iconic symbols.