Auditory Brainstem Response (ABR) or Brainstem Auditory Evoked Response (BAER) is a test that checks the brain’s response to sound. The test does not rely on a baby's response. The baby needs to be sound asleep or at a minimum very tranquil and not moving, so the brain response to very soft sound can be detected. If your child is younger than 6 months of age, the ABR test usually can be done while he or she naps, most often after feeding.