Pf. Dominey et Ts. Lelekov, Dissociable processes for learning the surface structure and abstract structure of sensorimotor sequences, J COGN NEUR, 10(6), 1998, pp. 734-751
A sensorimotor sequence may contain information structure at several differ
ent levels. In this study, we investigated the hypothesis that two dissocia
ble processes are required for the learning of surface structure and abstra
ct structure, respectively, of sensorimotor sequences. Surface structure is
the simple serial order of the sequence elements, whereas abstract structu
re is defined by relationships between repeating sequence elements. Thus, s
equences ABCBAC and DEFEDF have different surface structures but share a co
mmon abstract structure, 123213, and are therefore isomorphic. Our simulati
ons of sequence learning performance in serial reaction time (SRT) tasks de
monstrated that (1) an existing model of the primate fronto-striatal system
is capable of learning surface structure but fails to learn abstract struc
ture, which requires an additional capability, (2) surface and abstract str
ucture can be learned independently by these independent processes, and (3)
only abstract structure transfers to isomorphic sequences. We tested these
predictions in human subjects. For a sequence with predictable surface and
abstract structure, subjects in either explicit or implicit conditions lea
rn the surface structure, but only explicit subjects learn and transfer the
abstract structure. For sequences with only abstract structure, learning a
nd transfer of this structure occurs only in the explicit group. These resu
lts are parallel to those from the simulations and support our dissociable
process hypothesis. Based on the synthesis of the current simulation and em
pirical results with our previous neuropsychological findings, we propose a
neurophysiological basis for these dissociable processes: Surface structur
e can be learned by processes that operate under implicit conditions and re
ly on the fronto-striatal system, whereas learning abstract structure requi
res a more explicit activation of dissociable processes that rely on a dist
ributed network that includes the left anterior cortex.