Emotions play an important role in human communication. We conducted a study to identify the effect of emotions in language sounds in terms of brain functions. The sounds of Japanese sentences spoken with and without emotion were reversed to eliminate their semantic influence on the subjects’ emotional perception. Three sets of sentences with non-emotional and happy, sad, and angry emotional tones were recorded and reversed. The brain activities of 20 native Japanese speakers in their twenties were monitored by near-infrared spectroscopy (NIRS) while they listened to the reversed Japanese sounds with and without the emotions. Our analysis of the experimental results demonstrated that almost all the brain areas monitored by the NIRS probes were activated more when the subjects listened to emotional language sounds than to non-emotional sounds. In particular, the frontopolar cortex area, which is associated with short-term memory, was significantly activated. Since short-term memory is known to provide important information for communication, these results suggest that emotional aspects of language sounds are essential for successful communication and thus should be implemented in human–robot communication systems.
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