P300 and Feedback Provided by Absence of the Stimulus


  • This research was supported in part by a U.S.P.H.S. NINCDS grant. NS11199. We are indebted to Drs. Walter Ritter and Muriel Hammer and Ms. Janet Camp for a critical reading of the manuscript, and to Ms. Vilma Maschio and Mrs. Frances Pridgen for typing the manuscript.


This experiment is concerned with the issue of functional equivalence of emitted (in response to ahsence of a stimulus) and evoked (in response to presentation of a stimulus) P300s. Subjects attempted to estimate a 600-msec time interval hy the method of reproduction. Subjects were informed whether the time interval was under- or overestimated and whether the estimation error magnitude was within a limit (“correct” estimate, positive feedback) or exceeded the limit (“incorrect,” negative feedback). This feedback was presented by means of either a single event or a combination of two events. Each event consisted of a pair of stimuli.

Emitted, as well as evoked, early fronto-central and late parietal P3OOs were elicited by the feedback event regardless of whether positive or negative feedback was delivered, and regardless of whether feedback was delivered by a single event or by the combination of two events. In addition, what appears to be a positive Slow Wave was found following the first stimulus ofthe feedback event when this stimulus was low intensity indicating an underestimation. The other condition (high intensity, overestimation) was followed by a CNV. Since these slow wave findings were serendipitous, counterbalancing was not available to determine whether intensity (low vs high) or information (underestimation vs overestimation) was responsible for the difference.