This can be difficult because everybody has been overexposed to 440, which is nearly impossible to control for. Even if you log an effect it can be argued that the effect is not of 432 but of a certain deviation from a norm.
Eh, try it across a range of different tunings and see if there's a peak in the effect around 432. If there were, it would be easier for me to believe it's the 432 that's significant rather than "normal - 8Hz"