Our sense organs are perpetually inundated with information about the surrounding environment. Our severely limited capacity to process this deluge requires that we select for further processing only those aspects of the sensory world that are relevant to our current behavioral goals. Here, a series of experiments using event-related functional magnetic resonance imaging techniques addressed key questions regarding the brain mechanisms that mediate attentional selection of elementary visual features. One pair of experiments investigated whether specialized subregions of the attentional control network might be recruited in generating feature-specific control signals. In the first experiment, subjects were cued to expect specific colors or directions of motion on some trials, and on other trials they were cued to detect targets in one visual dimension but did not know which specific feature to expect. The second experiment served as a control for properties of the cue words themselves. All cue types elicited activity in a broad network of brain regions implicated in the control of selective attention but, critically, regions of dorsal frontal and parietal cortex were selectively activated by cues to attend for specific directions of motion. These areas were remarkably similar to those previously shown to be important for controlling attention to spatial locations, and both types of attention may be related to oculomotor planning. Another pair of experiments investigated whether attention-related pre-stimulus neural activity in feature-specific visual areas (a so called "baseline-shift") serves as the mechanism by which attention modulates responses to subsequent visual targets. The results of the first experiment failed to reveal any systematic relationship between baseline shifts and either target-evoked responses or target detection performance. The second experiment demonstrated that baseline shifts are not influenced by the presence of an irrelevant visual pattern between targets. These findings suggest that selective attention must invoke other mechanisms to modulate responses to attended stimuli. The results of both pairs of experiments are integrated into a larger framework drawn from current conceptualizations of working memory.
|Advisor:||Mangun, George R.|
|School Location:||United States -- North Carolina|
|Source:||DAI-B 68/09, Dissertation Abstracts International|
|Subjects:||Neurology, Psychobiology, Cognitive therapy|
|Keywords:||Attentional control, Neural mechanisms, Selective attention, Visual features|
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