Just as the advent of palm-sized organizers reduced our ability to recall dozens and sometimes even 100s of phone numbers of friends etc, AI will reduce our ability to perform a range of functions.
I think the evidence for this is quite clear. Humans are NOT going to expend any energy - even mental energy, to think about something if they don't have to.
Or Google Maps our ability to navigate when GPS signal is lost
But on the flip side of the coin, I've been traveling so much more since I got access to map software on my phone. Especially when vacationing abroad, remembering the days before smart phones, we would need to carefully plan specific attractions on a map ahead of time, and would generally not go far from these areas, unless we had the entire rest of the day available and didn't mind getting lost. But these days, I can be in a foreign city where I don't know more than a dozen words of the language and spontaneously pick a spot on the map and get there with local public transport in a very predictable time, being able to focus my time on deciding where I want to be, rather than how I get there.
Google Maps has made me a total idiot. I can't remember routes to places where I have gone quite a few times!