Awareness is necessary for differential trace and delay eyeblink conditioning in humans

Squire et al. have proposed that trace and delay eyeblink conditioning procedures engage separate learning systems: a declarative hippocampal/cortical system associated with conscious contingency awareness, and a reflexive sub-cortical system independent of awareness, respectively (Clark and Squire, 1998 and Smith et al., 2005). The only difference between these two procedures is that the conditioned stimulus (CS) and the unconditioned stimulus (US) overlap in delay conditioning, whereas there is a brief interval (e.g., 1 s) between them in trace conditioning. In two experiments using the same procedure as Clark and Squire's group, we observed differential conditioning only in participants who showed contingency awareness in a post-experimental questionnaire, with both trace and delay procedures. We interpret these results to suggest that, although there may be multiple brain regions involved in learning, these regions are organized as a coordinated system rather than as separate, independent systems.

► Differential Pavlovian eyeblink conditioning was only observed in participants who showed conscious awareness of the stimulus relationships.
► The relationship between conditioning and awareness was observed with both trace and delay procedures.
► The results contradict the proposal that delay conditioning is carried out by an automatic, unconscious system that is independent of other cognitive processes.