Why is L1 not easy to hear?

Abstract

We naively believe that L1 is easier to hear than L2. Generally, this belief is correct, but not always. Japanese contrastive focus is more challenging to identify than English focus even for L1 speakers. To account for why Japanese is hard to perceive, we first conducted production and perception experiments, to understand linguistic mechanisms.  We found that Japanese lacks a part of focus effects and is an acoustically weak language contra previous studies. English, on the other hand, is an acoustically strong language and uses the F0 feature as a focus cue. We then conducted an fMRI experiment to see whether or not linguistic mechanisms for them are implemented in the brain. We found that we employ different neural networks to process English and Japanese; the right dorsolateral frontal cortex is activated to process Japanese CF, but not English CF. Japanese is a pitch language and requires processing both lexical accents and pitch contours. English, on the other hand, needs to process lexical accent only, and it activates left superior temporal gyrus, insular, and supramargical regions, but not right dorsolateral frontal cortex. We conclude that processing burdens lead to perception difficulty, even for L1 Japanese speakers.