Contingent Negative Variation. An "expectation" response usually evoked by a stimulus that the subject associates with a second subsequent stimulus, often of a different modality. For example paired stimuli may be an auditory tone followed by a visual flash. If the subject has been repeatedly exposed to many pairs of these stimuli, not only does the tone evoke its own auditory response, a distinct response occurs in readiness for the flash, even if it is not given.