Asymmetric perception of HL and LH pitch patterns in Japanese

In Japanese, a lexically specified High–Low (HL) pitch accent distinguishes word meaning, whereas Low–High (LH) patterns typically occur post-lexically at the level of minor phrases. This raises the question of whether listeners are more sensitive to pitch patterns that serve lexical contrasts or less sensitive due to categorical perception. We conducted a perception experiment with native Tokyo Japanese speakers using an 11-step Fo continuum manipulated with a existing word /iru/ from HL (Step 1) to LH (Step 11). Results revealed a significantly sharp perceptual boundary. Step 6, in which both syllables have the equal Fo, was perceived as ambiguous. By Step 7, where the second syllable is slightly higher than the first one, stimuli were consistently perceived as LH. However, Step 5, despite featuring a higher Fo on the first syllable, was only identified as HL near chance level, suggesting that HL categorization requires a sufficiently steep Fo fall. These findings indicate an asymmetry in pitch accent perception: Fo must exceed a certain acoustic threshold to be reliably perceived as HL by Japanese native listeners. This result implies a perceptual imbalance caused by lexical prosodic constraints.