Integrating electrophysiology and neuroimaging of spatial selective attention to simple isolated visual stimuli

Visual-spatial attention involves modulations of activity in human visual c ortex as indexed by electrophysiological and functional neuroimaging measur es. Prior studies investigating the time course and functional anatomy of s patial attention mechanisms in visual cortex have used higher-order discrim ination tasks with complex stimuli (e.g. symbol matching in bilateral stimu lus arrays, or letter discrimination), or simple detection tasks but in the presence of complex distracting information (e.g. luminance detection with superimposed symbols as distracters). Here we tested the hypothesis that s hort-latency modulations of incoming sensory signals in extrastriate visual cortex reflect an early spatially specific attentional mechanism. We sough t evidence of attentional modulations of sensory input processing for simpl e, isolated stimuli requiring only an elementary discrimination (i.e. size discrimination). As in prior studies using complex symbols, we observed att ention-related changes in regional cerebral blood flow in extrastriate visu al cortex that were associated with changes in event-related potentials at a specific latency range. These findings support the idea that early in cor tical processing, spatially-specific attentional selection mechanisms can m odulate incoming sensory signals based on their spatial location and perhap s independently of higher-order stimulus form. (C) 2001 Elsevier Science Lt d. All rights reserved.