Early selective-attention effects on the evoked potential: a critical review and reinterpretation.

Recent research on the effect of selective attention on the N1, component of the evoked potential is reviewed. These studies are based on the finding of Hillyard Hink, Schwent and Picton (1973) that this component is selectively enhanced in response to attended stimuli when a very rapid rate of stimulus delivery is used. On the basis of the subsequent set of experiments, the conditions and limits of the existence of the auditory 'N1 effect' are now quite clear. Moreover, this finding has been extended to somatosensory and visual modalities. In the present review a detailed examination of these studies has suggested a re-interpretation of the N1 effect. According to this reinterpretation, it is not a 'true' N1 component which is enhanced but the effect is produced by a summation of a negative shift with the evoked-potential wave form. Under some conditions such as those involving a very fast rate of stimulus delivery, this effect commences very early, making the N1 component appear larger. It is suggested that this shift reflects orienting to, and further processing of, an input found relevant in a preliminary sensory analysis. Topographical evidence for this kind of interpretation is provided by several studies. This negative shift is, hence, associated with voluntary attention. Some of the reviewed studies have described a rather similar negative shift as a correlate of involuntary attention to rare stimuli among the much more frequent, 'standard', stimuli.