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Directing attention selectively to an expected event has already been known for a long time to recruit a network of frontal and parietal brain attentional control areas. In addition, this frontal-parietal control network has been hypothesized to signal stimulus-specific sensory (e.g. visual cortex) areas to increase preparatory (biasing) activity in an attempt to improve subsequent perceptual processing of the expected stimulus. The research presented in this thesis shows that there might actually be multiple, rather than one, frontal-parietal attentional control network, one being more medial-dorsal and the other being more lateral-dorsal in location. In addition, strong evidence was found for a frontal cortex initiation of top-down attentional control, rather than a parietal cortex initiation, as was hypothesized by some selective attention theories. Furthermore, it was found that the subsequently triggered sensory cortex biasing-related activity actually consisted of two different, coexisting, mechanisms: 1) a slow-wave baseline shift mechanism that can lower perceptual stimulus thresholds, and 2) an oscillatory alpha-frequency rhythm that can store an attentional trace (template), including both stimulus and response characteristics and their behavioral relevance. Finally, it was shown that voluntary choices in task strategies could selectively determine which frontal-parietal network would be activated (more medial-dorsal or more lateral-dorsal) and which sensory cortex mechanism would be selectively boosted. In short, an attention-for-perception based strategy recruits mostly a medial-dorsal frontal-parietal network and boosts most strongly the baseline shift mechanism, whereas an attention-for-action based strategy boosts more strongly the formation of an attentional template in sensory cortical areas. In conclusion, top-down attentional control is not a unitary mechanism, but includes multiple different processes that can be boosted selectively through voluntary choices in top-down task strategy.

Directing attention selectively to an expected event has already been known for a long time to recruit a network of frontal and parietal brain attentional control areas. In addition, this frontal-parietal control network has been hypothesized to signal stimulus-specific sensory (e.g. visual cortex) areas to increase preparatory (biasing) activity in an attempt to improve subsequent perceptual processing of the expected stimulus. The research presented in this thesis shows that there might actually be multiple, rather than one, frontal-parietal attentional control network, one being more medial-dorsal and the other being more lateral-dorsal in location. In addition, strong evidence was found for a frontal cortex initiation of top-down attentional control, rather than a parietal cortex initiation, as was hypothesized by some selective attention theories. Furthermore, it was found that the subsequently triggered sensory cortex biasing-related activity actually consisted of two different, coexisting, mechanisms: 1) a slow-wave baseline shift mechanism that can lower perceptual stimulus thresholds, and 2) an oscillatory alpha-frequency rhythm that can store an attentional trace (template), including both stimulus and response characteristics and their behavioral relevance. Finally, it was shown that voluntary choices in task strategies could selectively determine which frontal-parietal network would be activated (more medial-dorsal or more lateral-dorsal) and which sensory cortex mechanism would be selectively boosted. In short, an attention-for-perception based strategy recruits mostly a medial-dorsal frontal-parietal network and boosts most strongly the baseline shift mechanism, whereas an attention-for-action based strategy boosts more strongly the formation of an attentional template in sensory cortical areas. In conclusion, top-down attentional control is not a unitary mechanism, but includes multiple different processes that can be boosted selectively through voluntary choices in top-down task strategy.

Previously, we have shown that spatial attention to a visual stimulus can spread across both space and modality to a synchronously presented but task-irrelevant sound arising from a different location, reflected by a late-onsetting, sustained, negative-polarity event-related potential (ERP) wave over frontal-central scalp sites, probably originating in part from the auditory cortices. Here we explore the influence of cross-modal conflict on the amplitude and temporal dynamics of this multisensory spreading-of-attention activity. Subjects attended selectively to one of two concurrently presented lateral visually-presented letter streams to perform a sequential comparison task, while ignoring task-irrelevant, centrally presented spoken letters that could occur synchronously with either the attended or unattended lateral visual letters and could be either congruent or incongruent with them. Extracted auditory ERPs revealed that, collapsed across congruency conditions, attentional spreading across modalities started at approximately 220 ms, replicating our earlier findings. The interaction between attentional spreading and conflict occurred beginning at approximately 300 ms, with attentional-spreading activity being larger for incongruent trials. Thus, the increased processing of an incongruent, task-irrelevant sound in a multisensory stimulation appeared to occur some time after attention has spread from the attended visual part to the ignored auditory part, presumably reflecting the conflict detection and associated attentional capture requiring accrual of some multisensory interaction processes at a higher-level semantic processing stage.