======= ABSTRACT SUBMITTED TO ANNUAL MEETING of SFN, NOV, 1998 ====== EVIDENCE FOR EFFECTOR INDEPENDENT AND DEPENDENT COMPONENTS IN MOTOR SEQUENCE LEARNING. R. S. Bapi*, K. Doya. Kawato Dynamic Brain Project, ERATO, JST. Seika, Kyoto, Japan 619-0288. To investigate the representation of motor sequence, we tested transfer effects in a motor sequence learning paradigm. It is hypothesized that sequence representation is mediated by two componentsÑeffector independent and dependent. Six subjects were tested in a modified 2x10 task (Hikosaka et al., 1995). Subjects learned to press two keys (set) successively on a keypad in response to two lighted squares on a 3x3 display. Ten such sets called a hyperset was used. Training was given in the NORMAL condition and sequence recall was assessed during test blocks in the early and late stages in three conditionsÑNORMAL, VISUAL, and MOTOR. In VISUAL condition access of the arm to the keypad was rotated 90¡ while the keypad-screen mapping kept identical to NORMAL. In MOTOR condition the keypad-screen mapping was also rotated 90¡, resulting in an identical finger-screen mapping as in NORMAL. Reaction time (RT) and errors during recall were recorded. Errors did not significantly differ based on position showing that effector movements did not affect recall accuracy. With training, RTs in NORMAL and MOTOR conditions became similar and significantly lower than in VISUAL condition. Using RTs for single button pushing in different conditions as baseline indices, it was observed that RTs improved significantly in NORMAL & MOTOR conditions (from 26.5% & 22.8% in early stage to 46.5% & 42.6% in late stage, respectively). In contrast RTs in VISUAL condition improved slowly (from 21.3% to 33.3%), supporting the hypothesis that MOTOR condition benefits more than VISUAL because it uses identical effector movements to the NORMAL condition. Together these results extend the "effector independent sequence representation hypothesis," originally proposed for implicit sequences to explicit sequences. These results also support an effector dependent component in motor sequence learning which develops relatively slowly. The difference in the time course of learning may account for the differential involvement of brain areas in early and late learning phases found in lesion and imaging studies. (Internally funded)