Final answer:
Infants typically develop the ability to discriminate between the sounds [ba] and [ga] at around six months of age, as part of their auditory and cognitive development associated with language acquisition.
Step-by-step explanation:
Infants can hear the difference between the sounds [ba] and [ga] at around six months of age. This ability develops as part of their auditory perception and cognitive milestones. It aligns with the stage where babies start to engage in more complex vocal play and begin to babble, which is an essential precursor for language development. As infants grow, they refine their hearing and start to discriminate between phonemes, which are the distinct units of sound in a language. By the end of their first year, infants typically can discriminate among phonemes used in languages in their environment, so the differentiation of sounds such as [ba] and [ga] is part of this linguistic maturation process.