Implicit sequence learning processes after unilateral stroke

Implicit learning is durable over time, robust under psychological stress and shows specificity of transfer; characteristics that may be beneficial in stroke rehabilitation. The purpose of this study was to investigate implicit sequence learning processes in unilateral stroke using an extended number of trial blocks in a serial reaction time task (SRTT). Previous research, using a SRTT, has produced equivocal results that may be associated with the small number of trial blocks used. Seven adults, at least one year after stroke, and eight controls performed 54 blocks of a modified SRTT over two weeks. Participants responded with a finger key press during acquisition and retention and with a whole arm movement during transfer. Response times in milliseconds were used to measure learning. The stroke group performed more slowly than the controls during all experimental phases. Response times for both groups decreased with practice of the repeating sequence, increased with introduction of a random sequence, and decreased when reintroduced to the repeating sequence of the SRTT. Both groups demonstrated delayed retention of knowledge of the sequence over a two-week period and exhibited specificity of transfer. These data suggest that with extended practice people with unilateral stroke are able to learn implicitly.