Spatial attention has different effects on the magno- and parvocellular pathways

ATTENTION was directed to the left or to the right of the fixation point by the lateral presentation of a target on which the subject had to perform a n attention demanding task. A (task-irrelevant) grating displayed in the le ft visual field was the visual evoked potential (VEP) stimulus. Gratings mo dulated either in luminance or colour contrast at various temporal frequenc ies were used in order to maximise the activation of magno- or parvocellula r pathways. VEPs recorded in attended and unattended conditions were compar ed. For luminance stimuli, both latency and amplitude of VEPs were modified by attention. For chromatic stimuli, attention affected the amplitude but not the latency of VEPs. Spatial attention uses different mechanisms when m agno- or parvocellular systems are involved. (C) 1999 Lippincott Williams & Wilkins.