CNV and SPN: Indices of Anticipatory Behavior

Abstract

In the title of the first report about the Contingent Negative Variation (CNV) two things are suggested: The CNV is a sign of “sensori-motor association” and the CNV is an index for “expectancy” (Walter et al., 1964). In other words, the CNV reflects processes, which are, at first sight, quite different from the processes discussed in the other chapters in this book. Why then is it important to add a “deviant” chapter to this book? There are two reasons. First, the CNV is also a movement-preceding negativity (MPN), just as the Readiness Potential (RP). The RP reflects processes involved in the preparation of voluntary movements, and the CNV reflects processes involved in the preparation of signaled movements. In other words the RP and the CNV are both reflections of anticipatory behavior, at least as far as the motor system is involved. Moreover it doesn’t seem too difficult to put up a case for the view that most of our motor activity is elicited by the presence of some kind of stimuli, rather than being “voluntary”. This being a sufficient reason for a chapter on the CNV, there is a second reason. Anticipatory behavior is not restricted to the motor system; it involves attention to the surrounding and to stimuli, which are relevant for our ongoing behavior. This becomes clear in a simple paradigm such as the forewarned reaction time task, used to elicit a CNV. In such a paradigm, a warning signal (WS) alerts the subject to an upcoming imperative signal (RS) to which the subject has to respond, e. g. by pressing a button. The consequence is that the CNV is a MPN, confounded by activity related to anticipatory attention for the response signal (RS). This causes serious difficulty for the interpretation of the CNV. I will discuss later on a paradigm in which Separation in time of motor preparation and anticipatory attention is possible. The latter function is reflected in a second category of anticipatory slow waves: the Stimulus Preceding Negativity (SPN).