Influence of stimulus distance in implicit learning of spatial and nonspatial event sequences

The serial reaction time task has been widely used to investigate implicit learning mechanisms. In the present study, we investigated the effect of stimulus distance on learning of a spatial sequence independent of a sequence of responses. Participants had to respond to objects appearing at four different locations. The objects were presented in a sequence of nine elements, whereas the location at which an object was presented followed a sequence of eight elements. Thus, the spatial and the object sequences were independent of each other. Four groups of subjects for whom the distances of the locations chosen to present objects on the computer screen (3 cm, 6 cm, 12 cm, or 22 cm) differed were tested. Only the nonspatial sequence was learned as indicated by enhanced response latencies in nonsequenced random blocks. Stimulus distance had no effect on the amount of sequence learning. Additional analyses for subgroups of subjects who did not show explicit knowledge of the sequences after completion of the task indicated that for implicit learners also, sequence learning was not influenced by stimulus distance. The results are discussed with respect to current theories of implicit serial learning.