Anticipation of Relevant Stimuli and Evoked Potentials: A Comment on Donchin's and Cohen's “Averaged Evoked Potentials and Intramodality Selective Attention”

Donchin and Cohen (1967) reported having demonstrated amplitude differences of late components of occipital evoked potentials related to intramodal selective attention within the visual modality even under conditions in which the relevant stimuli could not be anticipated by S. They delivered flashes at irregular intervals from 2 to 3 sec. and, timed independently of these, background reversals at irregular intervals from 3 to 4 sec. on the same retinal location. The triangular test flash was superimposed on either of the background figures, one or the other of which was present at any given time. When S's attention was directed to the flashes, these elicited occipital potentials with larger late components than when attention was directed to the background reversals. Especially the late positive component (latency to peak 250 to 300 msec.) was considerably enhanced. The same effect was reported to have been observed with respect to the occipital potentials elicited by the background reversals. It is suggested here that the effect was actually induced by the anticipatory and preparatory reactions to the presentation of the relevant stimuli, conditioned by the regularities in the stimulus sequence. These differential anticipatory and preparatory reactions might include momentarily increased cortical activation as well as simultaneous changes in peripheral receptor conditions, such as improved ocular fixation and accommodation in addition to increased diameter of the pupil. In this author's view, these nonspecific factors may have caused the evoked potential amplitude differences between relevant and irrelevant visual stimuli which were interpreted by Donchin and Cohen to reflect intramodal selective attention.