Edward K. Vogel - US grants

DESCRIPTION (provided by applicant): Although we perceive our visual environment as stable, the information our brain receives from our eyes is continually disrupted through blinks and saccadic eye movements. Despite this "choppy" input, the visual world appears smooth and continuous. A critical process that is thought to underlie this phenomenon of "perceptual stability" is visual working memory, which facilitates the online maintenance and manipulation of visual information. Specifically, visual working memory may help tie the information obtained from one fixation to the next, so that a scene may be integrated across successive views. Recent research has made substantial advances in determining the extent of the memory that is maintained across saccadic eye movements. However, the specific nature of how information is compared and integrated across successive views has gone largely unexplored, and will be the primary concern of this proposal. In this proposal, we will examine how representations of objects are updated across changes in the position of the eyes and the focus of attention. For example, imagine viewing a scene of a cluttered desk in which a monitor, keyboard, and telephone are all within view in a single fixation. Following an eye movement to the left, each of these objects will now appear in a more rightward retinal position and it is necessary to update the positions of these objects so that they may be seen as old objects in new positions rather than new objects. One unanswered question regarding this updating process is when it occurs. Does it occur after the second fixation is made or is it more dynamic occurring as the eye movement is being programmed and executed, but prior to the actual fixation? Here, we will use the human eventrelated potential (ERP) technique to monitor the maintenance of information in visual working memory across changes in retinal position to determine when the updating process occurs. Moreover, we will also examine how changes in the focus of spatial attention within a single fixation affect the maintenance of information held in visual working memory. Specifically, does attending a new object disrupt or alter the representations of the current contents of memory? The outcome of these initial studies may serve as a basis for understanding the ways in which neurological damage can affect a patient's ability to understand and interact with the objects and events in the world.

Despite our phenomenological experience of a rich and detailed awareness of the objects in our environment, our immediate visual awareness is actually limited to a very small number of items at any given moment. The cognitive system that is thought to underlie this ability is visual working memory, which maintains active representations about objects in the environment so that they may be manipulated or acted upon. The storage capacity of this important system is well known to be highly limited. Working memory capacity is also well known to be subject to substantial individual differences. For over a century, individual differences in working memory capacity have been assumed to reflect "how many" pieces of information an individual can hold in memory at one time. In contrast, recent evidence suggests that variability in memory capacity may not be due to differences in absolute storage capacity, but instead may be due to differences in the ability to control attention. That is, because capacity is limited, efficient attentional selection mechanisms are necessary for controlling which items are maintained in working memory and which items will be excluded.

With support from the National Science Foundation, Dr. Edward Vogel and his colleagues at the University of Oregon will use behavioral and electrophysiological methods to examine the attention processes that control access to visual working memory and how these processes may differ across high and low working memory capacity individuals. They have recently developed a highly sensitive new neural method for measuring the amount of information a subject is currently holding in working memory, and will use this approach to establish behavioral and electrophysiological signatures of individual differences in control over working memory-related attentional processes. This work is important in part because an individual's ability to perform complex functions such as reasoning and mathematics has been shown to be greatly influenced by his or her working memory capacity. That is, high working memory capacity individuals tend to score much higher on general aptitude or scholastic achievement tests than low working memory capacity individuals. Working memory capacity is also known to be substantially lower in individuals with schizophrenia and attention deficit/hyperactivity disorder. Thus, a full understanding of the factors that underlie individual differences in working memory capacity may have broad implications in both educational and clinical settings.

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.

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.