Spatial Attention Improves Retinotopic Mapping
The visual world is represented in the brain in numerous retinotopic maps that extend along the cortical surface. Directing spatial attention to a given location in the visual scene enhances perception of that location, and strengthens the neural response to visual stimulation at the attended location. However, the effects of attention on neural responses differ across visual cortical regions.
This thesis is concerned with the study of the variety of effects of visual spatial attention on cortical responses. In the following chapters, we describe results from three major research projects. In the first project, we discovered that spatial attention improves response reliability (a signal-to-noise measure) in every cortical region we measured. The magnitude of these effects were greatest in regions with weak retinotopic signals, suggesting the importance of attention for discovering new areas of cortex with topographic organization. In the second project, we demonstrate that the attention-induced enhancement of response reliability results not only from a strengthening of the cortical response, but also a suppression of slow fluctuations in brain activity that are unrelated to the visual input. Moreover, the suppression of these slow fluctuations predicted performance on a visual detection task, whereas the enhancement of response magnitude did not. Finally, in the third project, we demonstrate attention's effect on response magnitude differs as a function of eccentricity; in early visual areas attention enhanced response strength the most for representations of central vision, whereas in dorsal regions attention enhanced response strength most for representations of peripheral vision. Moreover, we discovered that attention expanded the extent of visual space that generated a significant cortical response, and that this effect also differed across eccentricities and visual regions.