However, the TMT is a neuropsychological test with a ???floor effect???, which is the same in the STT. Almost all of the above indexes are not suitable in subjects who could not complete Part B. In our study, in cognitively normal controls, 1.5% subjects could not complete the STT-B. In patients with aMCI and mild AD, even more subjects failed in part B (4.8% and 30.4%).