Dissociation Between Electrophysiology and Behavior--A Disaster or a Challenge?
University of Illinois at Urbana-Champaign
It is the point of this chapter that some of the more interesting results in cognitive psychophysiology derive from instances in which the "behavioral" and the "physiological" observations appear to conflict. My thesis is that to seek interesting physiological "correlates" of psychological processes we should concentrate our effort on the search for physiological "dissociates" of behavioral processes. To illustrate this thesis I shall describe studies of the latency of the P300 component of the event-related brain potential (ERP). I shall also try to fulfill, in part, the tutorial mission of this discussion by highlighting some of the methodological problems encountered during the acquisition, and analysis, of ERPs. Due to time limitations, many of the details needed to support the various assertions are ignored.
An assertion that electrophysiological data need not correlate with behavioral data is not self-evident. On the contrary, much has been made of such dissociations. Most commonly, when a dissociation is found, the investigators conclude, with sorrow or with glee, that the data indicate that the electrophysiological signals are not meaningful, or valid, or interesting. A pithy, if not entirely original, statement of this conclusion by Clark, Butler, and Rosner ( 1969) was that evoked potentials are "full of sound and fury, signifying nothing." They supported this conclusion by purporting to show that stimuli of which the subject was still cognizant failed to elicit an ERP. Clark et al. believed that their data show that "perceptual response was obtained at levels of stimulation at which no AEP could be recorded." From this "dissociation of sensation and evoked responses" they inferred that "evoked activity . . . may play no essential