Answer: Infants dishabituated to /pa/ but not the "new" /ba/.
Step-by-step explanation:
Before the study by Peter Eimas and colleagues (Brown University, 1971) psychologists were unsure whether or not infants could recognize different phonemes.
Eimas found that even young infants seemed to recognize the difference between a ‘b’ sound and a ‘p’ sound.
Such results imply that we are born with the ability to categorize even imperceptibly different sounds, which is one of the basic elements of language learning.