Edward Awh - US grants

DECRIPTION (provided by the applicant): Visual selective attention is a crucial means of compensating for our limited ability to process multiple stimuli at one time. Observers can bias their perception of the visual world, selecting certain elements of a scene for full analysis while leaving others aside. While significant progress has been made in describing the spatial and temporal parameters of this ability (i.e. when and where spatial selection is possible), there has been less progress in understanding exactly how spatial selection is accomplished. The broad goal of this proposal is to provide insight into the specific mechanisms that mediate the changes in visual processing that are observed during visual selection. The proposed research investigates a previously undiscovered component of attentional control that causes increased levels of distractor exclusion when interference from distractors is likely. Previous research has shown that when stimulus displays contain high levels of visual noise, then spatial selection effects are enlarged. The key insight in this proposal is that some of these increases in selection efficiency are a result of changes in top-down attentional control, rather than being entirely display-driven. The present research is designed to understand the cognitive and neural basis of this mechanism of endogenous distractor exclusion. In addition, our work will address the overall architecture of attentional control, by comparing the behavioral and neural signatures of two forms of attentional control: the endogenous suppression of visual noise, and the top-down suppression of response conflict. By enhancing our understanding of top-down selection in visuospatial and response-mapping paradigms, the proposed research will contribute towards the ultimate goal of creating a unified model of executive processing.

DESCRIPTION (provided by applicant): Mental sets are high-level representations that regulate lower-level selection of action. Despite the relevance of mental sets for coherent and purposeful action, relatively little is known about how they are selected and maintained in the face of internal or external interference. The central thesis of this proposal is that a better understanding of set-level processes can be attained by looking at interactions between mental sets and lower-level representations that constrain action in a bottom-up manner (i.e., locations of stimuli or response keys). Specifically, an automatic process is proposed that binds action-related lower-level representations (e.g., stimulus or response locations) to the mental set that is in control of the action. Bindings between set-level and low-level codes should usually be in the service of stable and coherent goal-directed action. However, such bindings may get in the way of efficient control when the association between low-level and high-level codes is ambiguous or highly variable. In particular, problems should occur when high-level control is impaired, as in some patient groups and, albeit to lesser degree also in the context of normal aging. Interference elicited from bindings between high-level and low-level codes may also lie at the heart of executive-control deficits observed in old adults. Therefore, in a majority of the proposed experiments I suggest to explore the hypothesis that old adults are much more negatively affected by ambiguous mappings between low-level and set-level aspects than young adults. Such a result would point to age-related difficulties with "keeping apart" high-level representations that share low-level elements. The proposed project promises a bridge between lower-level perceptual/attentional processes and executive processes as well as answers to the important question of age differences in executive control.

DESCRIPTION (provided by investigator): Attention Deficit Hyperactivity Disorder is amongst the most commonly diagnosed mental health disorders. Recent estimates suggest that it affects 2-4% of adults, with consequences that include life histories of academic and occupational failure, interpersonal difficulties and stimulus seeking behaviors. One key challenge for developing our scientific understanding of ADHD is a paucity of objective measures of symptom severity. Such measures would provide valuable tools for basic research programs that call for continuous and quantitative measurements of the core deficits in ADHD subjects (endophenotypes) by allowing measurements of more subtle influences of disease precursors (e.g., genetic or environmental factors) than is possible with symptom checklists. We propose to investigate a psychophysical procedure for estimating an individual's ability to resolve visaul interference. Our preliminary data reveal that ADHD subjects have a severe deficit in discriminating targets in high interference displays, even though they show normal performance with equally challenging displays that do not contain distracting stimuli. These data suggest that ADHD subjects have a strong and selective deficit in the resolution of perceptual interference. We propose a comprehensive assessment of the integrity of visual interference resolution in well characterized ADHD and control popultions, with sample sizes large enough for a careful examination of the influence of co-morbid disorders and ADHD subtypes. In addition, we will use procedures developed within our lab that enable a selective manipulation of the degree to which interference is resolved at attended locations. These tasks, in conjunction with fMRI and event-related electrical recordings of the brain, will provide an in-depth analysis of the behavioral and neural characteristics for interference resolution in ADHD subjects, which may help to identify the underlying cognitive impairments that cause the severe disruptions in resolving interference in this population. Finally, given that most theories of ADHD suggest a modality independent deficit in attentional functions, we will examine whether ADHD subjects have similar difficulties with the resolution of interference in the auditory domain. Our initial studies will focus on the basic question of which dimensions within auditory perceptual space (i.e., spatial, temporal or spectral) provide the best analog to the spatial dimension that determines interference in the visual domain.

DESCRIPTION (provided by applicant): Working memory (WM) is a system for maintaining online representations of information in the service of virtually all explicit cognitive processes (e.g., memory retrieval, problem solving). WM's core role in cognition is also highlighted by strong correlations between WM capacity and fluid intelligence as various measures of scholastic achievement. Furthermore, deficits in WM performance are associated with prevalent clinical disorders, including attention deficit/ hyperactivity disorder (ADHD) and schizophrenia. The proposed research will address fundamental questions regarding the basic determinants of capacity limits in WM. Is capacity limited by a maximum number of items that can be represented simultaneously in WM? Or is it limited by the available mnemonic resolution (i.e., clarity) necessary for representing a given set of items? Our preliminary data suggest that rather than being determined by a single factor, number and resolution are distinct facets of WM capacity. The proposed research seeks to further detail how these two factors interact to limit WM performance by means of a combination of psychophysical procedures, human electrophysiological recordings (ERPs), and novel neural decoding techniques using FMRI. This project will focus on four critical questions regarding how the factors of number and resolution determine WM capacity. First, we will examine whether number and resolution limits for an individual are stimulus-specific or whether they reflect more stimulus-general limitations. Second, we will explore how individuals can voluntarily control the allocation of these two limited memory resources. Third, we will measure how an individual's implicit knowledge about likely target locations can influence the allocation of WM capacity. Finally, we will use multi-voxel pattern analysis (MVPA) on neuroimaging data to assess how visual sensory areas of cortex are recruited to help represent information in WM and whether they help to determine an individual's mnemonic resolution. Thus, the general goal of this research is to more finely characterize the nature of capacity limits in WM, and to further characterize the mechanisms that control access to this limited mental workspace. A better understanding of these basic research questions will enable a more precise characterization of psychopathologies that involve impaired cognitive processing, supporting both basic and translational research in the domain of mental health. PUBLIC HEALTH RELEVANCE: The core goal of the proposed research is to better characterize the nature of capacity limits in human working memory. This memory system is a core part of most cognitive processes, and capacity in this system is correlated with fluid intelligence and scholastic achievement. Because disruptions of working memory are common in prevalent clinical disorders such as ADHD and schizophrenia, a better understanding of the behavioral and neural underpinning of this system will have a beneficial impact on both the diagnosis and treatment of psychopathologies that involve impaired cognition.

DESCRIPTION (provided by applicant): Visual working memory (WM) is a central cognitive system for maintaining active representations about objects in the environment so that they may be manipulated or acted upon. Individual differences in WM ability in healthy populations appear to reflect a core cognitive ability because they strongly predict an individual's fluid intelligenc as well as several aspects of scholastic achievement. Furthermore, WM deficits are a signature of many prevalent mental health disorders. Thus, a detailed understanding of this system is essential if we are to understand and treat psychopathologies that involve impaired cognition such as attention deficit/ hyperactivity disorder (ADHD) or schizophrenia. In addition, because of the tight link between online visual memory and basic processes for visual perception, our work will help to integrate basic knowledge about visual sensory processing (e.g., population coding of simple visual features) and online memory. One of the most fundamental attributes of WM is that it is greatly limited in capacity: capable of storing information about just a few objects at time, each with a limited level of precision. A key recent discovery is that these number and precision limits are distinct facets of WM capacity. However, the neural mechanisms that underlie these two factors that determine capacity are not currently understood. Here, we are developing neural oscillatory and hemodynamic measures that enable tracking of both between- and within-subject variations in these abilities. Specifically, our preliminary data show that the number of items held in WM is indexed on a trial-by-trial basis by desynchronization in alpha power (8-12hz) and WM precision is indexed by the dispersion of sensory population codes (quantified via novel multivariate analyses of fMRI and EEG data). The proposed research will employ psychophysics, fMRI, and EEG to measure the neural signals that track number and precision in WM. These efforts will provide new insights into the functional subdivisions of visual WM, and build clear bridges between well characterized behavioral measures of online memory ability and measures of oscillatory activity in humans. Finally, we will also examine the interactions between visual WM and visual long term memory (LTM) to determine how the contents of WM determine that which is encoded into LTM. These studies will help to characterize the role of visual WM in associative learning and clarify the roles of each system in the guidance of complex behaviors. By more precisely understanding how healthy individuals differ in WM ability and visual sensory function, we hope to develop methods and procedures that can be used to more accurately detect and characterize disease states in populations with mental health disorders, and to diagnose and quantify disorders in visually-guided behavior.

PROJECT SUMMARY Visual working memory is a central cognitive system for maintaining active representations about currently relevant information. Individual differences in working memory ability reflect a core cognitive ability, as shown by robust correlations with fluid intelligence, scholastic achievement and other broad measures of intellectual function. Furthermore, working memory deficits are a signature of many prevalent mental health disorders, such as attention deficit/ hyperactivity disorder (ADHD), schizophrenia and depression. Thus, a detailed understanding of this system is important for understanding the cognitive effects of these disorders, and for precise assessments of the efficacy of clinical interventions. The broad goal of this proposal is to enhance our understanding of the neural signals that index storage in this online memory system, and to use those signals to refine cognitive models of human memory. A key recent discovery is that the electrophysiological signals that index storage in working memory can be divided into two distinct categories. One class of activity tracks the number of discrete ?items? or objects that are stored in working memory, without regard to the specific information associated with each object. A second class of activity instead tracks the spatial positions that are currently prioritized in the visual field, without regard to the number of independent objects occupying those positions. The proposed work will pursue this insight, refining both neural and cognitive models of human working memory. Finally, while working memory plays a critical role in complex cognition, there is a clear consensus that working memory must interact with qualitatively different memory systems (e.g., long term memory) that store information ?offline? or out of mind. While past work has often sought paradigms that allow a ?pure? assessment of working memory or long term memory, there is a strong need for work that directly examines the dynamic collaboration between these systems. Thus, a central theme of this project will be to identify the specific factors that encourage transitions between online and offline memory states. Specifically, the proposal will follow up on past work showing that observers divide up ongoing continuous experiences into discrete ?event? representations, and that the boundaries between events influence which pieces of information are integrated and segregated in memory. This project will use time-resolved electrophysiological measures of storage in working memory to determine whether event boundaries prompt the flushing of online memories to make way for information about subsequent events, even when there is adequate capacity for concurrent storage. This will provide new insight into the specific cognitive operations that determine how limited online memory capacity is deployed in complex cognitive tasks.