Post masking outlasts premasking and can skew frequency-modulation measurements by nearly 20 dB.

Evidence

Because post masking lasts much longer than premasking, these differences are to be expected. For a modulation frequency of 8 Hz, this effect becomes more pronounced leading to differences of almost 20 dB in masked threshold for the positions indicated by “2” and “6” at lower critical-band rates. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 547