Almost five years ago we showed that patients with pathologies of consciousness, such as the vegetative state, are able to learn the association between a tone and an airpuff to the eye (classic pavloviantrace conditioning) (Nature Neuroscience 12, 1343 - 1349 (2009). This constituted the first demonstration of associative learning in patients with pathologies of consciousness, and a confirmation of trace conditioning as one of the best objective strategies to assess awareness (since that trace conditioning seems to required awareness of the contingencies) without relying on voluntary motor or verbal responses. Since then we have concentrated in testing the limits of human cognition on classical conditioning and its underlying mechanisms (briefly reviewed in Front. Psychology (2011) 2:337).
The manuscript we put forward now addresses the relationship between classical conditioning and cognitive processes in two studies, suggesting healthy human volunteers can learn semantic category-to-US conditioning, that learning is modulated by attention, and is dependent on awareness of stimulus contingencies. Furthermore, when we probed awareness with perceptually masked CSs, learning only occurred in consciously perceived trials.
Conclusion: 1) awareness of the contingencies between CS and US seem to be required, 2) conditioning can be elicited with abstract stimuli as CS, 3) attention modulates degree of learning in a –most likely- nonlinear fashion, and 4) trace conditioning can be used to probe conscious processing.