Voice Onset Time is a good example of a distinctive feature that babies perceive, but we as adults may not.
In English, if we start the laryngeal tone exactly at the beginning of the "P" sound, it becomes (is perceived as) the "B" sound. If we delay progressively longer in small increments the beginning of the voice (voice onset time), there is a point in time that it would become the "P" sound. If a line under the wordd represents the beginning of the voice, it would look like this:
Because as babies, we were exposed to verbal experiences in which those phonemic boundaries were used, we can discriminate these sound differences today.
But there are some languages that include a Voice Onset time before the beginning of the consonant:
If the two words above were spoken and heard by a speaker of such a language, the two would be heard as different words--although to us they would sound and be the same.