It seems obvious to me that it takes some time for people to get used to using a new sense - particularly for higher-order abilities. Differentiating 'round' from 'hard edged' is probably a fairly simplistic function which your brain should be able to quickly figure out, but I don't see how it can just be instant.
I think this is exactly right. Tactile visual substitution systems provide a sensory modality that we may as well call sight, just not via the eyeballs, and it takes time for the blind to become capable with them. Why wouldn't it take time for them to become capable with a sensory modality that is causally associated with the eyeballs? And in fact, it does take time.
It seems obvious to me that it takes some time for people to get used to using a new sense - particularly for higher-order abilities. Differentiating 'round' from 'hard edged' is probably a fairly simplistic function which your brain should be able to quickly figure out, but I don't see how it can just be instant.