Subcortical gating in the human visual system during spatial selective attention

The question of whether subcortical gating occurs as a function of spatial selective attention remains unsettled. This issue was investigated, using the paradigm of Eason et al. (1969) wherein subjects are instructed to attend to a specified location in a given visual field while attempting to ignore stimuli presented in the opposite field. Visual evoked responses falling within the 40-70 ms range were found to be significantly more negative when the location at which the evoking stimulus appeared was being attended to than when it was not. Also, later deflections (100-200 ms) were enhanced in amplitude and negatively biased. The very early effect provides further evidence for spatial attention-induced precortical gating. The later effects provide additional evidence for the amplitude enhancement of 'exogenous' components, along with the possible involvement of glial cell activity in the generation of slow wave negativity.