Sound stimulus. Stimuli were grouped into two categories according to whether the sound was the same (S) as or different (D) from the preceding stimulus. In the present paradigm, the probability of the S trial and D trial was even. According to the number of same or different preceding stimuli, S stimuli were grouped into two subgroups (1S and 2S), and D stimuli into three subgroups (1D, 2D and 3D).
Inui et al. BMC Neuroscience 2010 11:135 doi:10.1186/1471-2202-11-135