Many years ago, I remember hearing of a psychology experiment where participants were asked to listen to two sounds and choose which one was higher or lower.
The two sounds were a mix of pure tones. If we number the standard notes numerically, then one sound would be all the even numbered notes and the other sound would be all the odd numbered notes. So, the two sounds should sound almost identical but that's not how they were perceived.
I can't remember who did the experiment, where, or what conclusions, if any, were drawn from the results.
Hoping someone else remembers it. Thanks.