The brain cannot fully scrutinize the wealth of information that is present at each moment, and so a selection process continually samples the environment. By determining which aspects of the environment receive preferred processing, this selection process undoubtedly has a huge influence on nearly all brain functions. An understanding of the neural mechanisms that collectively determine selection, broadly referred to as selective attention, has therefore been one of the great challenges of visual neuroscience. Selective attention is often guided by a combination of behavioral goals and stimulus salience. For example, the brain's limited processing resources can be deployed at a specific location either in anticipation of something important, or in response to a particularly strong or sudden stimulus. But selective attention is a dynamic and ongoing process, and introducing a bias toward a particular location is just one step in this process. Following deployment of the attentional spotlight, there is a subsequent cascade of attentional modulation that continues based on local object properties. Studies in humans have shown that enhanced processing at a cued location spreads within an object's visual boundaries, even when part of the object extends outside the task-relevant location. This stimulus-driven mechanism of selective attention, which can be construed as a refinement of spatial selection, has been referred to as "object-based spatial selection". Whereas the neural correlates of the first step in this continual selection process, spatial selection, have been well-characterized, the neural correlates of object- based spatial selection are unknown. The first objective of the present proposal is therefore to bridge this gap by characterizing attentional modulation in monkey extrastriate neurons attributable to stimulus-driven, object- based spatial selection, and then comparing it to attentional modulation attributable to goal-oriented spatial selection (within the same experimental task). A second objective of the present proposal is to determine the extent to which attentional modulation in extrastriate neurons is driven by other brain regions known to be part of the network of structures that mediate attentional selection, and to determine whether such interareal interactions vary depending on the mechanism of attentional selection. The central hypothesis is that spatial selection and object-based spatial selection are mediated through separable neural processes that interact to parse and filter the visual environment. We will probe these objectives and our central hypothesis by recording simultaneously from area V4, the pulvinar, and the frontal eye field (FEF) in monkeys trained on performing an attention task that simultaneously taps into goal-oriented spatial selection and stimulus-driven, object-based spatial selection. The multi-site recording technique will utilize fMRI- and DTI-guided electrode placement to define matching network nodes. Attentional disorders have severe consequences for human health (e.g., spatial neglect after stroke, ADHD). A necessary first step toward improving treatment of these disorders, and the goal of this proposal, is to gain a better understanding of the neural mechanisms of selective attention.
The proposed research aims to advance our understanding of the dynamic selection process that determines which parts of the environment, from moment-to-moment, receive preferred processing. This selection process is impaired in several clinical populations, including individuals with spatial neglect after stroke, ADHD, schizophrenia, and ASD. A better understanding of the extent to which attentional mechanisms are mediated through separable neural processes will lead to more pointed hypotheses about dysfunction in clinical populations, and thus have direct translational implications.
|Fiebelkorn, Ian C; Saalmann, Yuri B; Kastner, Sabine (2013) Rhythmic sampling within and between objects despite sustained attention at a cued location. Curr Biol 23:2553-8|