The serial reaction time task: implicit motor skill learning?

Since its development 20 years ago, the serial reaction time task (SRTT) has gone from being a tool used by psychologists (Nissen and Bullemer, 1987) to one that, in the last few years, has been embraced by a wider community (Fig. 1). Embedded within this task is a sequence, a connected series of events, that engages processes supporting the temporal organization of behavior, the formation of high-order associations, and the prediction of future events (Keele et al., 2004; Chafee and Ashe, 2007). Thus, this task has been used to explore the processes underlying a broad range of behaviors, including the cognitive and biological principles of learning and memory. Despite this success, it remains a task that is frequently misunderstood. Questions surround how task performance should be measured, whether it is appropriate to conceptualize the SRTT as an implicit learning task, whether it is a motor task, and whether it is dependent on the integrity of the medial temporal lobe (MTL). Here we briefly describe the SRTT and discuss these questions. An appreciation of these questions will aid the design and interpretation of future neuroscientific experiments. The serial reaction time task In this task, a visual cue can appear at any one of four positions arranged horizontally on a computer screen. Each screen position, designated 1– 4, corresponds to a button on a response pad. When a cue appears, at the start of each trial, a participant selects the appropriate response button, which ends the trial (Fig. 1). The duration of each trial, defined by the participant’s response time, is the primary task measure. At the end of each trial, there is a short fixed delay, often between 200 and 500 ms, before another cue is presented. The visual cues play out a repeating sequence of positions (for example, 2-3-1-4-3-2-4-1-3-4-2-1). These sequential trials are then followed by random trials in which the visual cue no longer plays out a repeating pattern of positions. Thus, the SRTT is an apparently straightforward four-choice reaction time task containing a repeating sequence that participants come to predict, and so learn. However, there are a number of misunderstandings and open questions that continue to surround this seductively simple task. Here we briefly touch on some of these issues.