Contingent negative variation

The contingent negative variation (CNV) was one of the first event-related potential (ERP) components to be described. The CNV component was first described by W. Grey Walter and colleagues in an article published in Nature in 1964. The importance of this finding was that it was one of the first studies which showed that consistent patterns of the amplitude of electric responses could be obtained from the large background noise which occurs in electroencephalography (EEG) recordings and that this activity could be related to a cognitive process such as expectancy.

Grey Walter and colleagues conducted the experiment in the chronometric paradigm. They had noticed that the electric response became attenuated, or habituated when a single stimulus is repeated. They also noticed that the amplitude of the electric response returned when a second stimulus was associated with the first stimulus. These effects were strengthened when a behavioral response was required for the second stimulus. In a chronometric paradigm, the first stimulus is called the warning stimulus and the second stimulus, often one that directs the subject to make a behavioral response, is called the imperative stimulus. The foreperiod is the time between the warning and imperative stimuli. The time between the imperative stimulus and the behavioral response is called the reaction time. The CNV, then, is seen in the foreperiod, between the warning and imperative stimulus.

Walter and colleagues also noticed that electric responses to warning stimuli seemed to have three phases: a brief positive component, a brief negative component, and a sustained negative component. They noticed that the brief components varied due to sensory modality, while the sustained component varied with the contingency between the warning and imperative stimuli and the attention of the subject. They labeled this component the “contingent negative variation” because the variation of the negative wave was contingent on the statistical relationship between the warning and imperative stimuli.

In their study, Walter et al. (1964) presented clicks or flashes, singly or in pairs, at intervals between 3-10 sec. The warning stimuli were single clicks or flashes and the imperative stimuli were repetitive clicks or flashes. The modality of the imperative stimuli was opposite that of the warning stimuli. The behavioral response was a button press which terminated the repetitive stimuli.

Walter et al. (1964) showed that a single click elicits a brief positive peak and a brief negative peak. Repetitive flashes elicit brief positive and negative peaks. If these stimuli are separated by 1 sec the same individual patterns result. After around 50 presentations, these peaks are indistinguishable from noise. On the other hand, when a single click is followed by the repetitive flashes which are terminated by a button press, there is a large gradual negative peak which ends sharply with the button press. This is the contingent negative variation. Another classical study was described by Joseph Tecce in the Psychological Bulletin in 1972. In this review, Tecce summarizes the development, morphology, and locus of appearance of the CNV.

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