The name's Andrew... Just Andrew.

Interesting, thanks!

If the great psychologist Roger Shepard were still with us, he might not have been surprised by this. He proposed a helix model for auditory pitch perception, with one octave per turn.
There is something very human about this finding. It's like catching an LLM counting on its fingers.

A thousand sci-fi body horror stories writing themselves in my mind as I read this abstract

Hmm, good point

AFAIK, before autism, the only real developmental diagnosis for children was "idiocy" (it went by many other names). Some children with autism probably got that label, but many would not have

My pet theory is that it was the introduction of universal education that made the difference.

Once all children had to go to school, it became possible/necessary to notice differences in how individual children behaved, in a way that previously never happened.