"Sensory gating" as a mechanism for visuospatial orienting: electrophysiological evidence from trial-by-trial cuing experiments.

Stimuli attended-to locations in visual space are usually detected with higher speed and accuracy than stimuli at unattended positions. It has been argued that this effect is due to "sensory gating" mechanisms that modulate the flow of perceptual information from attended and unattended positions. In the present experiments, event-related potentials (ERPs) were recorded to stimuli that were preceded either by a valid or by an invalid positional cue (trial-by-trial cuing). When overt responses were required only to infrequent target stimuli on valid trials (Experiment 1) or to all validly cued stimuli (Experiment 2B), but not to invalid trials, systematic enhancements of early sensory-evoked potentials were found. These effects were smaller when both validly and invalidly cued stimuli required a response (Experiment 2A). These findings are interpreted as evidence that sensory gating processes are activated during the trial-by-trial cuing of spatial attention. Furthermore, valid stimuli elicited a greater negativity than invalid stimuli at midline electrodes following the early enhancements of sensory-evoked potentials. This possibly reflects an additional enhanced processing of attended-to locations.