Attention is a critical factor in sensory and cognitive performance. Problems in controlling and directingattention can lead to serious deficits in performance and behavior. More complete information about the neuralmechanisms underlying attention will be important for understanding how it facilitates perception and guidesbehaviors. The proposed experiments will extend our understanding of the neuronal basis of attention by testing thehypothesis that attentional modulation depends on the same neuronal circuits that mediate sensory responsenormalization. Response normalization is a well-established mechanism that adjusts sensory signals based onthe overall activity in a large group of neurons with similar response properties. We propose that attentionalmodulations in visual cerebral cortex act through this normalization mechanism, such that attentionalmodulation cannot occur in conditions when normalization is weak or eliminated. We will test this hypothesis by using extracellular recordings to measure directly both attentionalmodulation and response normalization in the activity of individual neurons in cerebral cortex.
One specificaim i s to extend preliminary observations on the relationship between spatial attention and responsenormalization in two ways. First, although preliminary results have shown a correlation between attention andnormalization across neurons in the middle temporal visual area (MT), we will examine that relationship withinneurons by varying the spatial separation between pairs of stimuli in a way that will modulate normalization.Second, we will examine the relationship between spatial attention and response normalization in area V4, tosee whether they are correlated in a visual area with markedly different properties. The second specific aim is to examine whether feature-based attention, like spatial attention, is alsocorrelated with normalization. In one set of experiments, we will examine direction-based attention in MT,because direction-based attention is known to be robust in MT. In other experiments we will examine speed-based attention MT, which will provide a valuable comparison because speed is represented in a differentfunctional architecture than direction in MT. Collectively these experiments will provide a critical test of the hypothesis that attention depends onnormalization mechanisms. In doing so they have the potential of greatly extending our understanding of theneural mechanisms that underlie attention.
Attention is critical to perceptual and cognitive performance; and attention deficits are the most commonlydiagnosed behavioral disorder of childhood; with attention deficit hyperactivity disorder (ADHD) affecting asmany as 5% of children in the United States [35]. Better understanding of basic neuronal mechanisms relatedto attention and their interaction with sensory signals is needed for guiding assessment; diagnosis andtreatment of deficits of attention. The proposed research will investigate how attention affects visual signals incerebral cortex; and in particular how it interacts with sensory mechanisms involved in the integration ofmultiple visual stimuli.
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