Abstract
Recent studies have provided evidence for a neurobiological model of attention, in which a fronto-parietal network of brain areas is responsible for orienting, shifting, and maintaining the focus of attention. These control areas are hypothesized to send biasing signals to perceptual brain areas, which have the effect that the sensitivity of perceptual areas responding to the attended (i.e. relevant) stimulus features are increased, whereas the sensitivity of perceptual areas responsive to irrelevant stimulus features are attenuated. Such a model would predict a direct relation between the strength of attentional orienting and; a) an enhancement of sensory responses in visual cortex to attended stimuli, and b) a decrease in response time. Here we examined this prediction by relating the amplitude attention-shift related ERP components to reaction-times. This was done using Posner's symbolic cueing paradigm. A cue predicted the location of an imperative stimulus (50% valid, 33% non-informative, and 16% invalid) to which participants were required to make a speeded two-choice response. Validly cued trials were sorted according to reaction time. ERPs differed systematically as a function of response time. All validly cued trials showed a shift-related positivity in the cue-target interval, but this effect was attenuated on the slowest trials, indicating a reduction of attentional effectiveness. Imperative stimuli elicited P1 and N1 components, of which the N1 varied as a function of reaction time. Faster responses corresponded with a larger N1 amplitude, suggesting a direct correspondence between the efficiency of stimulus processing and the sensitivity of visual cortex.