When covertly attending to regions of space where behaviorally relevant information is expected to occur, processing of visual stimuli appearing at those locations is enhanced. Conversely, if a region of space is expected to be a locus of distracting events, processing of stimuli occurring there is attenuated. This latter suppressive process is reflected by retinotopically specific increases of alpha-band (8-15Hz) oscillatory power in the electroencephalogram. Based on the cellular physiology of similar oscillations in animals, it has been proposed that alpha might serve as a functional gating mechanism. Importantly, the network of neural areas that have been found to contribute to the generation of these rhythms, which include frontal, parietal and occipital visual areas and thalamic nuclei are the same areas implicated in several influential theories of attentional operations. Further characterization of the alpha-band measure is needed to determine the extent to which it is epiphenomenal to attentional deployment mechanisms, or rather an endogenous attentional mechanism per se. To date, the alpha-band measure of selective attention has only been characterized with respect to spatial attention. However, attention can also be deployed to non-spatial visual features, such as color or motion parameters, facilitating the processing of subsequent stimuli with the attended feature, independently of its spatial location. The goal of this project is to further characterize the alpha-band attentional measure by testing its spatiotemporal properties in a purely feature-based attention task. To this end, a classic visual spatial selective attention task will be transformed into a purely featural domain. A symbolic cue will inform participants about a task-relevant feature of an upcoming stimulus, while electrical brain activity is recorded at the scalp. The cue and imperative stimuli will be separated by an interval during which no stimulation occurs, the brain activity during which reflects internal preparatory attentional processes. By varying parameters of the cue (such as its informativeness) and imperative stimuli (such as its duration or coherence) contexts will be created for which different attentional sets are advantageous, allowing the assessment of the extent and limits of alpha-band power increases as a mechanism for suppression in biased competition models.
The ability to bias attention in favor of behaviorally relevant aspects of the environment is critical for good mental health. Disruptions of normal attentional function, and in particular the ability to suppress irrelevant information, has been implicated in many psychiatric disorders such as attention deficit disorder, autism spectrum disorders and schizophrenia. The contributions of this project to understanding the neurophysiological mechanisms underlying normal attentional suppression will greatly advance research of disorders involving attention. This work dovetails nicely with ongoing research in our laboratory and with collaborators concerning autism spectrum disorders and schizophrenia.
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