EVENT-RELATED POTENTIAL CORRELATES OF NONMOTOR ANTICIPATION

A slow negative shift called "stimulus-preceding negativity" (SPN) has been observed preceding feedback. The aim of the present study is to investigate whether the SPN is related to perceptual or conceptual anticipation. Event-related potentials (ERPs) were recorded in an S1-S2-S3 sequence with intervals of 3 s. S1 was an auditory warning signal; the task stimulus presented at S2 consisted of two digits on which subjects (n = 8) performed an arithmetic task. They had to match their solution with a probe stimulus presented at S3. Perceptual anticipation was manipulated by varying the discriminability of S2 (intact vs. degraded). Conceptual anticipation was manipulated by varying the amount of information processing required at S2 (easy vs. difficult arithmetic). Motor preparation was varied by requiring a speeded versus a delayed response. No negativity was found before the task stimulus (S2), whereas the probe stimulus (S3) was always preceded by a negative shift. The amplitude of this negative shift was larger under the speed than under the delayed instruction. Its amplitude showed a left-hemisphere preponderance and was larger for the difficult than for the easy condition. ERPs preceding task stimuli seem to reflect functionally different processes from ERPs preceding probe and feedback stimuli. The difference is explained in terms of motivational factors that come into play with feedback and probably play a role in the anticipation of the probe stimulus.