Ghost beat

[Oleg Isaac]

Hello

When heating the thirds beat without concentration on the 5:4 partial, I
hear a kind of "ghost beat at the upper note level (i;e; at het A3 level
for a F3 A3 third.

The beats seems to be a little bit slower than the partial beat.

Is there a consensus to explain that. (I read Virgil Smith's article on
the "pure tone hearing" subject)

Any input, any reading ?

Thank you in advance.

Isaac OLEG