Phoneme quality and quantity are processed independently in the human brain.
In speech perception, the primary cue of phoneme recognition is typically the spectral quality of the speech sound. In some languages, however, even speech-sound duration may serve as a phonological cue. This distinction is called quantity. We used a component of event-related potential, the mismatch negativity, to determine whether phoneme quality and quantity are processed independently in the human brain. We found that the mismatch negativity responses to phoneme quality and quantity changes are additive, indicating that the analysis of these features is independent of each other. This suggests that phoneme quality and quantity are processed by separate neural processes that, in a system model, may be regarded as different levels in the phonological system.