Over the course of language acquisition, the brain becomes specialized in the perception of native language speech sounds or phonemes. As a result, adult speakers are highly efficient at processing their native language, but may struggle to perceive some non-native phonemes. This specialization is thought to arise from changes that occur in a person’s brain as a result of maturation and language experience. In this study, adult native speakers of English were asked to discriminate between phonemes of varying degrees of difference from English (similar to English: Tagalog /na/-/ŋa/; different from English: Ndebele /k||i/-/k!i/), as their brain activity was measured using functional near infrared spectroscopy imaging. The left inferior frontal region showed activation only during the native condition; this finding is discussed in the context of developmental and adult neuroimaging work and suggests that the left inferior frontal region is critical for perceiving native phoneme contrasts during development and in adulthood.