430 Fig. 1 An example of a ten-trial sequence (A–D–B–C–A–C–B– D–C–B) of the Pattern Learning Task (PLT). The upper panel shows the pen trajectories, and the lower panel displays the absolute velocity of the ten trials. The upper panel depicts the four possible target locations (A, B, C and D) (visible for the participant as open black circles), as well as the cursor (real color: dark blue) and the target (real color: red) positioned at the start of the Wrst movement (from A to D). Directional errors were made in the 5th trial (from A to C) and the 8th trial (from D to C), because these trajectories started in a direction (determined at the periphery; shown as a dotted circle only for A), which deviated by more than 22.5 degrees from the ideal direction. The display seen by the partici- pants consisted only of the dark blue pen cursor and the four black circles (one Wlled red as the target) positioned in the middle of the PC screen Exp Brain Res (2011) 214:427–435 design (two implicit sequence learning tests) necessitated the participants remaining naive with regard to the Wxed sequence till the end of the test session. Data analysis and statistical analysis Learning in the SRTT and the PLT involves both visuomo- tor learning and sequence-speciWc learning. Accordingly, the general decrease observed across learning trials—in this study from block R1 to block L4—is interpreted as the combined result of these two learning components. How- ever, from block L4 to block R2, the eVect of task-speciWc sensorimotor learning will be minimal compared with the disruption caused by the change from a Wxed target sequence to a random sequence. The diVerence between the second random block (R2) and the previous Wxed-sequence block (L4) can be regarded as a measure of sequence learn- ing (Knopman and Nissen 1987). Sequence learning is also reXected by an increase in the number of errors made when the order of the stimuli changes from Wxed (in block L4) to random (in block R2). Therefore, an increase in reaction time (RT) and in the proportion of errors (pressing the wrong button) recorded in the second random block (R2) relative to the fourth Wxed-sequence block (L4) were used as measures of implicit sequence learning for the SRTT. Only correct responses were included in the RT analysis. 123 PLT performance was recorded and analyzed by means of OASIS software (De Jong et al. 1996). In this task, the increase in total time (TT) in the last random block (R2) relative to that recorded in the last Wxed-sequence block (L4) was taken as a measure of implicit learning. TT was subsequently divided into the time needed to initiate a movement (RT) and the time needed to cross the distance between the two circles (movement time or MT). RT was deWned as the time between stimulus presentation and the time at which the pen left the start circle and crossed its 0.4-cm periphery (total diameter: 3.4-cm). This value was measured rather than velocity (a change from standstill to movement) because participants were allowed to start mov- ing the pen toward the anticipated next stimulus before it was actually displayed. This instruction stimulated partici- pants to move more or less continuously, with only very short intermittent stops, between successive target move- ments, but made it impossible to deWne reaction time based on a velocity threshold. MT was deWned as the time taken to cross the distance between the periphery of the start cir- cle and the periphery of the target circle. The TT, RT, and MT analyses excluded trials in which a directional error had been made. Directional errors in the PLT (DE; see Fig. 1) were deW- ned as movements that left the start circle at the wrong angle, i.e., deviations >22.5 degrees from the most optimal