The experiments that Dowling talks about show that there is this period where you will lose these abilities if you dont use them. It is much harder to lose them afterward and much harder to recover them. For example, he says “If in a young animal a closed eyelid is opened after a short period of deprivation, little recovery is observed after months to years of the eye remaining open.” A trick that ophthalmologists have learned is to put a patch over the good eye so the bad eye can gain more neurons in the visual cortex.

Anyway so the point is not that we lose these abilities permanently, we can obviously re-learn them. But its much easier to use them when your brain is first wired for them than to lose them and have to re-learn them later.