2005 — 2007 |
Tjan, Bosco S |
R03Activity Code Description: To provide research support specifically limited in time and amount for studies in categorical program areas. Small grants provide flexibility for initiating studies which are generally for preliminary short-term projects and are non-renewable. |
Uncertainty and the Order of Visual Processing in Cortex @ University of Southern California
[unreadable] DESCRIPTION (provided by applicant): Knowing the connections between different brain regions and the direction of the flow of information along these connections is of paramount importance for understanding the functioning of the visual system both in its healthy and diseased states. By adapting a body of theoretical and empirical results from basic research in low-level visual psychophysics, we propose that functional magnetic resonance imaging (fMRI) can be used to image the flow of information without the need of a very high temporal resolution. With reasonable assumptions, we can show that when noise is added to a visual stimulus, the impact of this noise on neural activity will depend on the amount of nonlinear processing that occurs between the stimulus and the brain region of interest. This general effect leads to a number of fMRI-measurable quantities that we can use to determine the input-output ordering between adjacent cortical areas and subregions. The goal of this study is to develop and test this novel method, based on clear-cut predictions from the underlying theory, in those cortical regions of the human visual system where large-scale connectivity is reasonably well known. [unreadable] [unreadable]
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2008 — 2016 |
Tjan, Bosco S |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Form Processing in Peripheral Vision @ University of Southern California
[unreadable] DESCRIPTION (provided by applicant): The overall goal of this study is to identify the sources of form-vision deficits in peripheral vision. Macula is the high-resolution patch in a human retina, which provides clear and sharp "central" vision. Patients with various forms of macular disorders, such as aged-related macular degeneration, must see objects eccentrically and rely on their low-resolution peripheral visual fields to recognize objects, identify faces and read. Compared to the fovea, the periphery is far less capable of this type of form vision, even when its poor spatial resolution is compensated for by magnification and contrast enhancement. For example, reading in the periphery is laboriously slow, and objects can become unidentifiable in a cluttered scene. At present, we do not have a good understanding of how form vision in the periphery is achieved by the visual system, why peripheral form vision is qualitatively different from central vision, and what are the causes of the form-vision deficits in the periphery. Such lack of understanding hinders our ability in deriving effective rehabilitation regimens and adaptive technologies for patients with central vision loss. Our focus is to investigate form vision in the periphery with ecologically important stimuli (faces, objects, and letters). We hypothesize that form vision deficits in the periphery are largely due to a lack of mechanisms for properly selecting and assembling simple features into complex ones at an early stage of visual processing. We further hypothesize that practice improves peripheral form vision mostly by improving the visual system's ability to make better inference about the misassembled inputs at the later stages. Our investigation is divided into three interrelated parts. Parts 1 will use psychophysical and computational methods to identify the functional causes of form vision deficits in the periphery. Part 2 will use fMRI to locate the brain regions that are associated with these deficits in order to provide converging evidence for the findings from Parts 1. Part 3 will determine the functional and neural mechanisms that underlie form-vision learning in the periphery. We will conduct experiments on normally sighted young adults, patients with central vision loss, and older adults (aged-matched controls for the patients). PUBLIC HEALTH RELEVANCE: The most common cause of visual impairment in the older population is age-related macular degeneration (AMD), which accounts for about 50% of all cases of registered blindness in industrialized countries (Koh & Ang, 2002). Patients with AMD and other macular disorders must view objects eccentrically and rely on their peripheral visual fields to recognize objects, identify faces and read. These form-vision tasks are often laborious if not impossible. The overall goal of this study is to identify the sources of form-vision deficits in peripheral vision, which we believe will enable the development of effective rehabilitation regimens and adaptive technologies. [unreadable] [unreadable] [unreadable]
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2012 — 2014 |
Tjan, Bosco |
N/AActivity Code Description: No activity code was retrieved: click on the grant title for more information |
Eager: Separating Bold Nonlinearity From Neuronal Nonlinearity in Human With Achiasma @ University of Southern California
Functional magnetic resonance imaging (fMRI) is a noninvasive technique for observing brain activity. It is difficult to overestimate the role fMRI plays in the modern study of neuroscience. While fMRI is an indispensible tool for studying the neural system, the specific relationship between neural activity and the most commonly used fMRI signal, called the blood oxygenation level dependent (BOLD) signal, is not well understood. With funding from the National Science Foundation, Bosco Tjan, Ph.D., of the University of Southern California, is determining the precise linkage between neural activity and the BOLD signal by studying the visually-evoked BOLD signal in the brain of an achiasmatic person. Achiasma is a rare congenital condition; a person with achiasma is born without an optic chiasm, which is the part of the brain where half of the nerve fibers from each eye cross over to reach the opposite side of the brain. Achiasma's unusual development of the visual system has striking effects upon the mapping of the visual world onto the visual cortex. Normally, there is a one-to-one topological relationship between a point in the visual world and a location on an early visual cortical area. For example, when looking at the center of a clock face, each of the numbers on the clock face is projected to one distinct location on the primary visual cortex. In contrast, when an achiasmatic person looks at the same clock face, the symmetric locations about the vertical midline are projected to the same cortical locations in the early visual areas. For example, the numbers 4 and 8 on the clock face are both projected to the same location in the primary visual cortex, while the numbers 5 and 7 are both projected to a nearby location. Fortunately, an achiasmatic person does not confuse the left from the right half of a clock face, or the visual world for that matter. As it turns out, there are two comparable groups of neurons packed in the same cortical location in the visual cortex of an achiasmatic person, with one responsible for a left location of the visual world, and the other for the symmetric right location. These two groups of neurons appear to function independently of each other, but nevertheless share part of the same blood supply. By presenting identical stimuli to one or both sides of a pair of symmetric locations about the vertical midline, the investigator can effectively half or double the underlying neural activity that drives the blood supply at that location, without knowing the exact relationship between the stimulus and the absolute amount of the evoked neural activity. He can then measure the resulting fMRI BOLD signal, which is a signal related to the local blood flow, blood volume and blood oxygen concentration, and thereby characterize the mathematical relationship between neural activity and the BOLD signal.
Knowing the quantitative relationship between the BOLD signal and the underlying neural activity is of the utmost importance. It will allow researchers to use noninvasive fMRI measurement to quantify the underlying neural activity everywhere in the brain. In cognitive neuroscience, we may one day be able to use fMRI to quantitatively measure certain psychological constructs and provide deeper insight into the mechanics of the brain. For example, if the level of neural activity in a brain area is believed to be proportional to the subjective value of a reward a study participant has received, then observing noninvasively an x% change in the fMRI BOLD signal will allow a researcher to infer that the subjective value of the reward has changed by y%. The current investigation, although focused on the arguably aberrant visual system of an achiasmatic subject, can have a broad and sweeping impact on many subfields of cognitive neuroscience by providing a unique and decisive data set relating neural activity to the fMRI BOLD signal.
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0.915 |
2015 — 2016 |
Tjan, Bosco S |
U01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Human Connectomes For Low Vision, Blindness, and Sight Restoration @ University of Southern California
? DESCRIPTION (provided by applicant): Worldwide, over 285 million people are visually impaired, and 39 million of those are blind. Visual impairments (blindness and low vision) severely and negatively impact the quality of life. New sight-restoration treatments have arrived for some blinding diseases. An electronic retinal prosthesis is approved for sight restoration in advanced retinitis pigmentosa. Gene therapy trials have shown promise for Leber's congenital amaurosis. Stem cell treatments for age-related macular degeneration are starting clinical trials. In some cases, remarkable results have been demonstrated, suggesting that at least partial vision restoration is possible after prolonged blindness. However, psychophysical data from clinical trials often show large variance in outcomes. Preconditions in brain structure and function associated with the central visual pathway (CVP) may underlie some of the variance. The effect of complete blindness upon the brain is well studied, but most ophthalmologic disease produces effects that vary from point-to-point across the retina. How does the precise topography of eye disease map onto changes in brain? Is acquired retinal damage related to local effects upon the structure and function of the CVP? Are any of these effects of vision loss on the CVP reversible? We propose to answer these questions, which we believe are crucial to the on-going efforts in developing sight- restoration treatments, by combining advanced retinal imaging with the brain-mapping techniques developed in the Human Connectome Project (HCP), using novel yet robust analytical methods. We will reveal the relationships between retinal pathology and their downstream impact on the CVP in unprecedented detail over the natural courses of blinding diseases and their treatments. We will make available to the research community the raw and processed data on retinal pathology for a range of blinding diseases, along with neuroimaging data collected with the HCP protocol. We will provide the computer codes used to extract relevant features from the retinal and neural datasets and the statistical models that relate the two. The extensive datasets and the associated data-analysis tools will form a transformative foundation for studies of neural plasticity associated with visual impairments and sight restoration.
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