How Implicit Sequence Learning and Explicit Sequence Knowledge Are Expressed in a Serial Response Time Task

Sequence learning in the serial response time task (SRTT) is one of the few learning phenomena that are widely agreed to be implicit in nature (i.e., that learning may proceed in the absence of awareness), while it is also possible to explicitly learn a sequence of events. In the past few decades, research into sequence learning largely focused on the type of representation that may underlie implicit sequence learning, and whether or not two independent learning systems are necessary to explain qualitative differences between implicit and explicit learning. Using the drift-diffusion model, here we take a cognitive-processes perspective on sequence learning and investigate the cognitive operations that benefit from implicit and explicit sequence learning (e.g., stimulus detection or encoding, response selection, or response facilitation). To separate the processes involved in expressing implicit versus explicit knowledge, we manipulated explicit sequence knowledge independently of the opportunity to express such knowledge, and analyzed the resulting performance data with a dynamic drift-diffusion model to disentangle the contributions of the aforementioned processes on. Results revealed that implicit sequence learning does not affect stimulus processing, but benefits response selection. Moreover, beyond response selection, response execution was affected. Explicit sequence knowledge did not change this pattern if participants worked on probabilistic materials, where it is difficult to anticipate the next response. However, if materials were deterministic, explicit knowledge enabled participants to switch from stimulus-based to plan-based action control, which was reflected in ample changes in the cognitive processes involved in performing the task. First implications for theories of sequence learning, and how the diffusion model may be helpful in future research into implicit and explicit sequence learning, are dicussed.