Exp Brain Res (2011) 214:427–435 angle. Thus, in the PLT an error only reXects the choice of a nonoptimal movement direction in the Wrst phase of the movement toward the target, a direction that can be cor- rected during the later stages of the movement. An increase in error rate in block R2 relative to that recorded for L4 was taken to indicate implicit sequence learning. Repeated-measures multivariate tests (GLM) were con- ducted with block (2 levels: L4-R2) as within-subject factor and group (patients vs controls) as between-subject factor. Overall group diVerences were analyzed over blocks R1-L4. Furthermore, repeated-measure multivariate analyses (GLM) were conducted with block (2 levels: L4-R2) as within-subject factor and explicit knowledge (explicit knowledge vs no-explicit knowledge) as between-subject factor in both the patient and control group. Alpha was set at 0.05 throughout the study. Correlations were computed between reaction time and percentage of errors to investi- gate the speed-accuracy trade-oV in both tasks. Results SRTT performance The mean RTs for the two groups on each of the six blocks are presented in Fig. 2. As expected, the controls had signiWcantly lower mean RTs than the patients (F(1,32) = 17.30, P < 0.001), and, also as anticipated, both groups showed implicit learning of the Wxed sequence, as reXected by an increase in RT between blocks L4 and R2 (F(1,32) = 97.23, P < 0.001). The increase from L4 to R2 was not signiWcantly diVerent between the groups: the interaction between Group and Block was not signiWcant (F(1,32) = 1.99, P = 0.168). The mean SRTT error rate on the six blocks for both groups is presented in Fig. 3. The percentage of errors did not diVer signiWcantly between the groups (F(1,32) = 0.57, P = 0.46) and increased signiWcantly between blocks L4 and R2 (F(1,32) = 10.74, P = 0.003). The Group £ Block interaction was not signiWcant (F(1,32) = 0.74, P = 0.395). Correlations between error rates and RTs in blocks L4 and R2 within the two groups were not signiWcant (L4: r = 0.12 and r = 0.03; R2: r = ¡0.07 and r = ¡0.16 for patients and controls, respectively). PLT performance Figure 4 presents the means and standard errors for the TTs, RTs, and MTs on the six blocks of the PLT for both groups. The controls had signiWcantly lower mean TTs than the patients (F(1,32) = 19.23, P < 0.001), and both groups showed implicit learning of the Wxed sequence, as shown 431 Fig. 2 Mean reaction times per group for the random blocks (R1 and R2) and the Wxed-sequence blocks (L1-L4) of the Serial Reaction Time Task (SRTT). Error bars reXect standard errors Fig. 3 Mean error rates across the random blocks (R1 and R2) and the Wxed-sequence blocks (L1-L4) of the Serial Reaction Time Task (SRTT) by the increase in TT between blocks L4 and R2 (F(1,32) = 39.08, P < 0.001); the Group £ Block interac- tion was not signiWcant (F(1,32) = 0.64, P = 0.430). The increase in RT between blocks L4 and R2 reXects implicit mastery of the Wxed sequence in both groups (F(1,32) = 41.23, P < 0.001); the Group £ Block interaction was not signiWcant (F(1,32) = 1.12, P = 0.297). The MTs in blocks L4 and R2 (F(1,32) = 8.93, P = 0.005) also revealed a between-block diVerence; however, for both groups, the MTs were signiWcantly lower in block R2, not higher. The Group £ Block interaction was not signiWcant (F(1,32) = 2.19, P = 0.148). 123