The fundamental goal of perception is to infer the structure of the world through an interpretation of temporal and spatial regularities in sensory stimulation that map onto structures in the environment such as objects and surfaces. The goal of this proposal is to trace the emergence of low-level object processing operations as they evolve in time and cortical area and to study how rapid, on-line learning or adaptation modifies these responses. We propose to study the mechanisms by which the visual system segments the visual scene into objects and surfaces and how it adapts its responses to stimuli with varying levels of temporal regularity using a combination of EEG source-imaging and functional MRI techniques in normal adults. In the first Aim we will study how attention interacts with low-level mechanisms involved in figure-ground segmentation. A novel, multi-input stimulation and analysis method will be used to separate response to figures and their backgrounds. In the second Aim, we will determine how temporal predictability shapes the accuracy behavioral shape discrimination by correlating behavioral performance with activity in visual and control areas that occurs before the presentation of predictable targets. A second goal is to determine if anticipatory evoked activity made in response to temporally regular stimuli can occur implicitly.
The third Aim will record responses to predictable and unpredictable stimuli of varying degrees of salience. Anticipatory activity will be isolated by subtracting reconstructions of the evoked response derived from random stimuli from those measured with temporally regular stimuli over a range of stimulus salience. These data will be used to test the hypothesis that anticipatory activity is generated in prefrontal cortex and produces its largest effects in target areas of occipital/occipital temporal cortex for low salience stimuli.
The tasks we will study require integrated activity throughout the visual hierarchy, in executive control areas of pre-frontal cortex and in areas responsible for sensory motor integration and motor response. The methods we develop to link brain activity and behavior at each of these levels will be relevant to understanding and managing disorders of visual processing, visual memory, visuo-motor integration and motor execution. Because the methods are non-invasive they can be applied directly to clinical populations in future studies of Cortical Visual Impairment, traumatic brain injury, stroke, dementia and congenital brain malformations. These disorders frequently compromise visual processing and each often involves significant compromise of motor and cognitive functions. Careful adaptation of the protocols that will be developed in this proposal may provide information relevant to the diagnosis and management of these disorders.
