Extraction of contingencies between features of successive auditory stimuli was studied by exploiting the mismatch negativity component of the event-related potential. According to the rules hidden in the stimulus sequences, one stimulus feature (duration) predicted another feature (pitch) of the next stimulus. Occasional deviant stimuli, violating the rules, elicited a mismatch negativity although the participants were ignoring the stimuli. Mismatch negativity was also elicited when the participants tried to detect the deviant stimuli. Their detection performance, however, was poor and on the basis of subsequent interviews, they were not consciously aware of the rules. The results suggest that contingencies across-features of successive stimuli are extracted already at the early preattentive level in the auditory sensory memory.