Attentional shifts have little effect on the waveform of the chromatic onset VEP.

Attention is important for sufficient performance on many visual tasks. This has been shown using achromatic steady-state and pattern-reversal VEPs. Waveform characteristics typically attenuate when attending to distractor stimuli and ignoring VEP stimuli. Chromatic pattern-onset responses have not been tested under conditions of selective attention: as they can be used in clinical settings to test color vision, it is important to know what effects attentional shifts would have on this response. In the present study chromatic pattern-onset VEPs were recorded using spatially divided and spatially contiguous VEP and distractor stimuli. VEP stimuli were 1 cycle.deg(-1) horizontal sine wave patterns (onset mode 100 ms on/400 ms off) used to selectively modulate the L-M and S-(L+M) visual pathways. Distracter stimuli were letters. Subjects attended to either the letters or the gratings and pressed a button when a predetermined stimulus appeared. In Experiment one, VEP and distractor stimuli were superimposed and spatially contiguous. In Experiment two, stimuli were presented to different hemifields. No significant changes in waveform amplitude and latency were found between VEP and distractor attention conditions for either visual pathway. For the chromatic pattern-onset response, modulation of attention does not change responses either with spatially contiguous or spatially separate selective attention manipulations. Consequently, it may not be necessary to monitor attention during recording of this response.