Topographic Brain Mapping of Transient Visual Attention

Abstract

Longitudinal studies of patients with multiple sclerosis require not only determination of the well-known PI 00 in the context of pattern visual evoked potentials, but also an analysis of potentials being related to cognitive processes (Sutton etal. 1965). We therefore developed the visually elicited P300 by using two different kinds of checkerboard stimuli (A and B) which were randomly flashed to the subjects out of the gray background of a TV screen (Taghavy and Kügler 1985, 1986a, b). Systematic analysis of the PFP300 complexes revealed the following results: The PFP300 complexes are composed of a clearly recognizable negative wave peaking at about 250 ms (N250) followed by a sharp positive potential rise (PFP300) which is terminated by a negative potential decay (N400). Since the latencies of those peaks were closely related to different stages of information processing, we called the preceding negativity (N250) the “differentiating potential,” PFP300 the “processing potential” and N400 the “terminating potential. ” We also found marked changes of the PFP300 amplitudes. These were in general about 3 times higher in the PFP300 complexes elicited by the rare, task-relevant B stimuli than in those elicited by the frequent, task-irrelevant A stimuli (Taghavy and Kügler 1986 a). These amplitude variations were caused mainly by differing degrees of attention toward the eliciting stimuli. The subjects, who had to keep a running total in their heads of the infrequent B stimuli only, had to stay alert for the appearance of the rare B stimuli throughout the experiment in order to perform the task selectively (“sustained attention”). In contrast the degree of attention paid to A stimuli had only to be sufficient to differentiate them from the B stimuli (“floating attention”).