The linear regression N1–P1 slope of VEP amplitudes over all blocks differed significantly between the three groups (F2,74 = 12.219, p < 0.0001, partial η2 = 0.248, op = 0.995; raw data are shown in Fig. 2). Post-hoc analysis showed that the slope of N1–P1 VEP amplitude changes over all 6 blocks was less steep in MA and in MA+ patients than in HV (p = 0.0001, p = 0.001 respectively, raw data are shown in Fig. 3), but it was equally steep between MA subgroups (p = 0.894).