When obvious covariations are not even learned implicitly

The present experiments examine the impact of covariation type and attention on implicit covariation learning. Experiments 1 and 2 compare learning of stimulus–stimulus (s–s) and stimulus–response (s–r) covariations. Although stimuli and responses were predicted by a distinct feature of the display, implicit learning neither of s–s nor of s–r covariations was observed. Experiments 3–5 explore the impact of attention on implicit learning of an s–r covariation. Distinct features either of the targets or of an incidental but centrally presented object predicted the responses. Implicit covariation learning was restricted to predictors that were part of to-be-attended targets. Finally, Experiment 6 shows implicit learning of a partial s–r covariation in which only one of two responses is predicted by target features. It is argued that implicit learning is based on the formation of associations between simultaneously activated distinct representations. Because only attended stimuli seem to reach a sufficient level of mental distinctiveness, attending the predictive information most likely is an indispensable prerequisite for implicit covariation learning to occur.