[en] Procedural learning refers to the ability to learn new perceptual, motor or cognitive skills. While many studies have explored procedural learning abilities in patients with different types of brain damage, the cognitive mechanisms involved in the acquisition of a new skill are still not well understood. The present review focuses on the conditions that optimize skill acquisition, and more specifically on the contextual interference effect (CIE), which refers to the advantage of a ‘random’ over a ‘blocked’ practice condition in skill learning tasks. According to both the ‘elaboration’ and ‘reconstruction’ hypotheses, the CIE can be explained by the fact that the random schedule requires more cognitive activity than the blocked one. However, if the CIE has been consistently demonstrated in laboratory studies, it is not so clear in fieldbased studies. We discuss this ‘laboratory and field dilemma’, and suggest that two main factors – task complexity and individual variables – may explain the discrepancy between the two types of studies.