Attentional Limits to Visual Perception

Vanderbilt University, Nashville TN

Investigators

Abstract

Visual scenes contain far more information than can be perceived consciously at any given instant. The information that does reach visual awareness is selected by attention. However, since attention has very limited processing capacities, it constrains severely the amount of visual information accessible for visual perception. Surprisingly little is known about the circumstances under which attention limits perception and about the neural substrates that underlie these restricted attentional capacities. By using a combination of behavioral and functional magnetic resonance imaging (fMRI) experiments, this research will examine the behavioral conditions under which attentional capacities are strained, and it will map out the brain regions that are responsible for these capacity limits. The research will use the attentional blink (AB) paradigm as a model for understanding the neural correlates of attentional limits to visual perception. The AB refers to a severe but transient (about half a second) impairment in detecting the second of two target objects presented amidst a rapid sequence of objects. The blink occurs when attentional mechanisms are consumed by the processing of the first target, leaving little attention available to perceive the second target, which hence may go undetected. Thus, the AB can be used as a measure of attentional capacity limits. One series of experiments will determine the conditions that trigger the attentional blink. While it is well known that the presence of multiple objects in a visual scene can compete with a target for attentional resources, this research will determine whether other conditions that render a target less discernable may also drain attentional resources. Another series of experiments will examine whether increasing the difficulty in perceiving an object, such as by decreasing its visibility, is sufficient to increase attentional demands and generate an AB. The research will also determine the generality of the capacity-limited process revealed by the AB. Do various forms of attention, namely task-driven (top-down) and stimulus-driven (bottom-up) attention, show similar capacity limits? Do other sensory modalities, namely the auditory system, also show capacity limits like the visual AB, and do they tap on the same attentional resources as the visual system? And finally, are the attentional resources necessary to perform perceptual tasks such as letter identification the same as those required when performing motor tasks, such as response selection? The experimental approach will be first to determine behaviorally whether different forms of attentional processes show capacity constraints, and then to carry out a series of fMRI experiments to determine the neural substrates which mediate these capacity-limited processes. A massive amount of visual information can be processed in parallel in the initial stages of visual information processing. However, soon the information enters some capacity-limited stage(s) that severely limit the amount of visual information that can reach conscious perception. These experiments will reveal the behavioral conditions that produce bottlenecks, and fMRI data will determine where the bottlenecks occur along the visual information-processing pathway in the human brain. This research should therefore reveal important insights into the neuro-architecture of human visual information processing, and it will also advance our understanding of the link between attention and visual perception.