Learning a covert sequence of effector movements: limits to its acquisition

Abstract

Sequence learning in serial reaction time (SRT) tasks is an established, lab-based experimental paradigm to study acquisition and transfer of skills based on the detection of predictable regularities in stimulus and motor response sequences. Participants learn a sequence of targets and responses to these targets by associating the responses with subsequently presented targets. In the traditional paradigm, however, actions and response targets are directly related. In contrast, the present study asked whether participants would demonstrate acquisition of a sequence of effector movements of the left vs. right hand (e.g., hand sequence learning), whilst the actual targets and associated finger responses are unpredictable. Twenty-seven young adults performed a SRT task to visually presented characters with the index or middle fingers of both hands. While the specific fingers to respond with were randomly selected for each target presentation, both hands followed a covert sequence. We asked whether participants would learn the underlying hand sequence as demonstrated by shortened response latencies and increased accuracy compared to a fully randomized hand sequence. The results show sequence-specific learning effects. However, categorization of hand responses depending on the previous response suggested that learning occurred predominantly for subsequent finger responses of the same hand, which added to general hand-based priming. Nevertheless, a marginally significant effect was observed even for predictable shifts between hands when homologous fingers were involved. Our results thus suggest that humans are able to benefit from predictable within-hand finger shifts but less so for predicted shifts between hands.

Fig. 1

Performance curves of the response latencies (A) and percent error (B). In Blocks 1, 2 and 10, the sequence of stimuli was random, while in the remaining Blocks 3 to 9 as well 11 and 12 the respective hand sequence was presented 20 times. Error bars represent 95% confidence intervals

Fig. 2

Performance curves of the response latencies (A) and percent error (B) as a function of the finger shift within or between hands. In the Blocks 1, 2 and 10, the sequence of stimuli was random, while in the remaining Blocks 3 to 9 as well 11 and 12 the respective hand sequence was presented 20 times. Error bars represent 95% confidence intervals