About
68
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Introduction
My research focuses on sensory neuroscience, using behavioral, genetic, and high resolution neuroimaging techniques to investigate questions ranging from the fundamental organization of human visual cortex, functional plasticity in visuomotor regions, and visual changes in dementia, to the organization of human auditory cortex.
Current institution
Additional affiliations
July 2007 - present
January 2000 - December 2007
Education
March 2000 - September 2005
September 1997 - June 2007
September 1991 - June 1996
Publications
Publications (68)
One of the fundamental properties of the mammalian brain is that sensory regions of cortex are formed of multiple, functionally specialized cortical field maps (CFMs). Each CFM comprises two orthogonal topographical representations, reflecting two essential aspects of sensory space. In auditory cortex, auditory field maps (AFMs) are defined by the...
Significance
We use functional MRI to investigate the cortical effects on V1, V2, V3, hV4, and VO-1 when humans’ eyes have adapted to low-light vision. We show that populations of neurons with receptive fields interacting with the central rod scotoma are silenced because of lack of stimulation, shift their locations ectopically, and/or scale their...
The functional organization of human auditory cortex has not yet been characterized beyond a rudimentary level of detail. Here, we use functional MRI to measure the microstructure of orthogonal tonotopic and periodotopic gradients forming complete auditory field maps (AFMs) in human core and belt auditory cortex. These AFMs show clear homologies to...
Several aspects of cortical organization are thought to remain plastic into adulthood, allowing cortical sensorimotor maps to be modified continuously by experience. This dynamic nature of cortical circuitry is important for learning, as well as for repair after injury to the nervous system. Electrophysiology studies suggest that adult macaque prim...
Human visual cortex is organized into distinct visual field maps whose locations and properties provide important information about visual computations. There are two conflicting models of the organization and computational role of ventral occipital visual field maps. We report new functional MRI measurements that test these models. We also present...
Cortical processing pathways for sensory information in the mammalian brain tend to be organized into topographical representations that encode various fundamental sensory dimensions. Numerous laboratories have now shown how these representations are organized into numerous cortical field maps (CMFs) across visual and auditory cortex, with each CFM...
Human sensory systems are organized into processing hierarchies within cortex, such that incoming sensory information is analyzed and compiled into our vivid sensory experiences. Computations that are common to these sensory systems include the abilities to maintain enhanced focus on particular aspects of incoming sensory information (i.e., attenti...
One of the fundamental properties of mammalian brains is that sensory regions of cortex are organized into multiple, functionally specialized cortical field maps (CFMs). An individual CFM is composed of two orthogonal topographical representations, reflecting two essential aspects of a sensory feature space. Each CFM is thought to subserve a specif...
The cortical hierarchy of the human visual system has been shown to be organized around retinal spatial coordinates throughout much of low- and mid-level visual processing. These regions contain visual field maps (VFMs) that each follows the organization of the retina, with neighboring aspects of the visual field processed in neighboring cortical l...
This chapter reviews the differences in specific structural and functional characteristics of human visual cortex among young adults, healthy aging adults, and patients with dementia, with a primary focus on those with Alzheimer's disease (AD). Such visual cortex changes have been shown to underlie many of the behavioral deficits that develop in he...
This paper describes a conformal geometry based approach to objectively quantify the retinotopic organization of selected regions within the early human visual areas. The approach proposes using the Beltrami coefficient to measure the angle distortion of the mapping between the visual field and the V1 visual area. By treating the retinotopic mappin...
The cortical organization of the human auditory system has been incompletely measured. While we know some of the features and locations of low-level processing in cortex, we were not until recently able to localize individual auditory field maps (AFMs). The key insight to measuring AFMs was recently discovered: two orthogonal acoustic dimensions, t...
In 2000, monocular vision was restored to M. M., who had been blind between the ages of 3 and 46 years. Tests carried out over 2 years following the surgery revealed impairments of 3-D form, object, and face processing and an absence of object- and face-selective blood-oxygen-level-dependent responses in ventral visual cortex. In the present resear...
Brain-derived neurotrophic factor (BDNF) is the most abundant neurotrophin in the brain, influencing neural development, plasticity, and repair (Chen et al., 2004; Thoenen, 1995). The BDNF gene contains a single-nucleotide polymorphism (SNP) called Val 66 Met. The Met allele interferes with intracellular BDNF-trafficking, decreases activity-depende...
The ultimate goal of many fields of neuroscience research is to harness the ability for the human
brain to reorganize, as an understanding of how to induce plasticity in cortex could foster the
development of treatments of such devastating conditions as paralysis, neurodegenerative
disease and stroke. The specifics of the timing and types of reorga...
Functional magnetic resonance imaging (fMRI) has been widely used to measure the retinotopic organization of early visual cortex in the human brain. Previous studies have identified multiple visual field maps (VFMs) based on statistical analysis of fMRI signals, but the resulting geometry has not been fully characterized with mathematical models. H...
Although several studies have suggested that cortical alterations underlie such age-related visual deficits as decreased acuity, little is known about what changes actually occur in visual cortex during healthy aging. Two recent studies showed changes in primary visual cortex (V1) during normal aging; however, no studies have characterized the effe...
A primary organizing principle of visual cortical organization is the visual field map: neurons with visual receptive fields next to one another in visual space are located next to one another in cortex, forming one complete representation of visual space. Similarly, we have shown that auditory cortex is organized into auditory field maps: neurons...
Serotonin (5-HT) is a neuromodulator that has been attributed to cost assessment and harm aversion. In this review, we look at the role 5-HT plays in making decisions when subjects are faced with potential harmful or costly outcomes. We review approaches for examining the serotonergic system in decision-making. We introduce our group's paradigm use...
Game theory is commonly used to study social behavior in cooperative or competitive situations. One socioeconomic game, Stag Hunt, involves the trade-off between social and individual benefit by offering the option to hunt a low-payoff hare alone or a high-payoff stag cooperatively. Stag Hunt encourages the creation of social contracts as a result...
Visual working memory (VWM) is the ability to maintain visual information in a readily available and easily updated state. Converging evidence has revealed that VWM capacity is limited by the number of maintained objects, which is about 3 - 4 for the average human. Recent work suggests that VWM capacity is also limited by the resolution required to...
The search for organizing principles of visual processing in cortex has proven long and fruitful, demonstrating specific types of organization arising on multiple scales (e.g., magnocellular / parvo-cellular pathways [1] and ocular dominance columns [2]). One of the more important larger scale organizing principles of visual cortical organization i...
Aging often results in reduced visual acuity from changes in both the eye and neural circuits [1-4]. In normally aging subjects, primary visual cortex has been shown to have reduced responses to visual stimulation [5]. It is not known, however, to what extent aging affects visual field repre-sentations and population receptive sizes in human primar...
Game theory has been useful for understanding
risk-taking and cooperative behavior. However, in studies of the
neural basis of decision-making during games of conflict, subjects
typically play against opponents with predetermined strategies.
The present study introduces a neurobiologically plausible model
of action selection and neuromodulation, wh...
Introduction. Recent work demonstrates that there may be specific genetic profiles that predict the capacity for neural plasticity. Polymorphisms in the BDNF gene correlate with memory capacity and synaptic plasticity (Egan et al, 2003; Kleim et al, 2006), and may predict capacity for visual-motor learning and motor map plasticity (Pearson-Fuhrhop...
Knowledge of the normal organization of visual field map clusters allows us to study potential reorganization within visual cortex under conditions that lead to a disruption of the normal visual inputs. Here we exploit the dynamic nature of visuomotor regions in posterior parietal cortex to examine cortical functional plasticity induced by a comple...
Are ectopic responses in lesion projection zones (LPZs) the result of long-term reorganization (plasticity) or short-term filling-in (adaptation)? We used field-standard travelling-wave and cutting-edge population receptive field (pRF) model functional MRI visual field mapping techniques with 4 types of flickering checkerboard stimuli under photopi...
Aging typically results in reduced visual acuity, both from changes within the eye and from acquired neural deficits. It is not known, however, to what extent aging affects visual field map organization in human cortex. In addition, patients with Alzheimer's disease (AD) often present with visual deficits as one of their earliest complaints. It is...
Game theory has been useful for understanding risk-taking, cooperation, and social behavior. However, in studies of the neural basis of decision-making during games of conflict, subjects typically play against an opponent with a predetermined strategy [1-3]. In the present study, human subjects played Hawk-Dove games against a neural agent, both si...
Introduction: The phenomenon of perceptual filling-in, where a region of the retina does not transmit visual information, yet we perceive visual information based on what information is available from nearby retinal locations, has been studied extensively at the blind spot (e.g., Ramachandran, 1992) and after inducing “artificial scotomas” (retina-...
Introduction: One of the more important larger scale organizing principles of visual cortical organization is the visual field map: neurons whose visual receptive fields lie next to one another in visual space are located next to one another in cortex. As increasing numbers of visual field maps have been defined in human visual cortex, one question...
Introduction: Human occipital cortex contains several distinct foveal representations, but mainly those on the ventral surface respond preferentially to color over luminance-matched stimuli. We made fMRI measurements to learn more about these ventral signals. Methods: We examined the fMRI BOLD signal in human ventral occipital (VO) cortex using (1)...
Introduction: In this study, we exploit the dynamic nature of posterior parietal cortex to examine cortical functional plasticity induced by a complete reversal of visual input in normal adult humans. Using retinotopic fMRI measurements, we have previously demonstrated changes within the spatial representations of multiple parietal visual field map...
Introduction: Visual working memory (VWM) capacity has been shown to be limited by the number of items one can hold in memory and the resolution at which those items are represented. The number limit appears to be subserved by cortex in inferior interparietal sulcus (IPS), while the resolution limit seems to be subserved by superior IPS and part of...
Introduction: Conventional visual field mapping contrasts stimuli at a series of visual field locations. Visual field map estimates identify the most effective stimulus position at each cortical location. Conventional methods (a) do not include a blank period, so that it is impossible to know whether all stimuli cause some response, and (b) summari...
Human visual cortex comprises 4-6. billion neurons that are organized into more than a dozen distinct functional areas. These areas include the gray matter in the occipital lobe and extend into the temporal and parietal lobes. The locations of these areas in the intact human cortex can be identified by measuring visual field maps. The neurons withi...
Introduction: Primate visual cortex can be partitioned into distinct visual areas which serve separate perceptual functions. One important organizing principle within many visual areas is a topographical map of visual space, also called a visual field map. The organization within these maps follows the organization of the retina; hence, retinotopic...
A recent study of a child born with one cerebral hemisphere has revealed an extreme developmental reorganization of visual cortex. Self-organizing visual maps demonstrate a surprisingly flexible restructuring in response to cortical loss.
INTRODUCTION. The rod and cone photoreceptors of the retina are organized such that the central fovea contains no rod photoreceptors. It is generally accepted that this pattern of organization continues through the input into the early retinotopic visual areas in human occipital cortex. Thus, signals from both rod and cone photoreceptors travel fro...
Stratton (Psych. Rev., 1897) first described visuomotor adaptation to altered visual input by wearing inverting prism spectacles. A number of studies (e.g., Miyauchi et al., J. Physio., 2004) have tried to confirm his findings and further examine the question of how responses in visual cortex change during this adaptation process. There is evidence...
Several studies have examined the role of primate parietal cortex in visuomotor tasks involving grasping, reaching, and saccadic eye movements (e.g., Hagler et al., Neuroimage, 2007). One especially useful way to study that role is to measure how motor systems adapt to alterations in visual input. Neuroimaging measurements in humans have begun to r...
Much of the visual cortex is organized into visual field maps: nearby neurons have receptive fields at nearby locations in the image. Mammalian species generally have multiple visual field maps with each species having similar, but not identical, maps. The introduction of functional magnetic resonance imaging made it possible to identify visual fie...
This review describes measurements of visual field maps and color signals in human visual cortex. One of the most exciting advances in recent years has been the ability to measure more than a dozen visual field maps in human visual cortex. These maps are grouped into small clusters that share a common eccentricity
representation; we speculate that...
We disagree with Calford et al. that there is a consensus on adult plasticity in primate V1 cortex: for example, macaque area V1 cytochrome oxidase levels remained depressed for several months after binocular retinal lesions; no reorganization in macaque V1 after monocular retinal lesions was found; and no area V1 reorganization in a patient with m...
Diffusion tensor imaging (DTI) and fiber tracking (FT) were used to measure the occipital lobe fiber tracts connecting the two hemispheres in individual human subjects. These tracts are important for normal vision. Also, damage to portions of these tracts is associated with alexia. To assess the reliability of the DTI-FT measurements, occipital-cal...
We describe the location and general properties of nine human visual field maps. The cortical location of each map, as well as many examples of the eccentricity and angular representations within these maps, are shown in a series of images that summarize a large set of functional MRI data. The organization and properties of these maps are compared...
BACKGROUND. Regions within human visual cortex have different computational specializations. We are exploring the temporal and chromatic responses across visual cortex to learn more about the specializations for color. METHODS. Retinotopic maps were measured in three human subjects using small (3 deg radius) expanding ring and rotating wedge stimul...
Recovery after long-term blindness was first studied¹ in 1793, but few cases have been reported since2, 3, 4, 5, 6, ⁷. We combined psychophysical and neuroimaging techniques to characterize the effects of long-term visual deprivation on human cortex.
The position, surface area and visual field representation of human visual areas V1, V2 and V3 were measured using fMRI in 7 subjects (14 hemispheres). Cortical visual field maps of the central 12 deg were measured using rotating wedge and expanding ring stimuli. The boundaries between areas were identified using an automated procedure to fit an at...
We describe the first systematic functional magnetic resonance imaging (fMRI) measurements of visual field maps in macaque visual cortex. The boundaries of visual areas V1, V2, V3, V3A, V4, MT/V5, and TEO/V4A were identified using stimuli that create traveling waves of activity in retinotopically organized areas of the visual cortex. Furthermore, t...
ional homologies between the two species. Key words: visual cortex; visual areas; cortical magnification; fMRI; monkey; human; extrastriate cortex Functional magnetic resonance imaging (fMRI) provides new perspectives on the organization of visual cortex in both human and monkey brains (Logothetis et al., 1999; Wandell, 1999; Tolias et al., 2001; V...
Human colour vision originates in the cone photoreceptors, whose spatial density peaks in the fovea and declines rapidly into the periphery. For this reason, one expects to find a large representation of the cone-rich fovea in those cortical locations that support colour perception. Human occipital cortex contains several distinct foveal representa...
h the new hemi# eld representation and further anterior in the ventral occipital lobe. Keywords: colour; retinotopy; visual cortex; cerebral achromatopsia; V4; V8 1. INTRODUCTION In his insightful review of the neurological literature on cerebral achromatopsia and colour anomia, Meadows (1974) argued that several cortical regions are essential for...
We describe a compelling demonstration of large-scale developmental reorganization in the human visual pathways. The developmental reorganization was observed in rod monochromats, a rare group of congenitally colorblind individuals who virtually lack cone photoreceptor function. Normal controls had a cortical region, spanning several square centime...
Functional MRI measurements can securely partition the human posterior occipital lobe into retinotopically organized visual areas (V1, V2 and V3) with experiments that last only 30 min. Methods for identifying functional areas in the dorsal and ventral aspect of the human occipital cortex, however, have not achieved this level of precision; in fact...
Functional MRI measurements can securely partition the human posterior occipital lobe into retinotopically organized visual areas (V1, V2 and V3) with experiments that last only 30 min. Methods for identifying functional areas in the dorsal and ventral aspect of the human occipital cortex, however, have not achieved this level of precision; in fact...
Human visual cortex comprises 4–6 billion neurons that are organized into more than a dozen distinct functional areas. These areas include the gray matter in the occipital lobe and extend into the temporal and parietal lobes. The locations of these areas in the intact human cortex can be identified by measuring visual field maps. The neurons within...
Questions
Question (1)
I am looking for a recommendation for a working memory task (n-back, visuospatial, ....) for an undergraduate project in my lab that can be run remotely online. With quarantine in place, we are not able to use our custom, in-person software. We had planned to compare working memory capacity among particular groups of interest, but, in the current scramble to finish this project before graduation and during quarantine, any basic working memory task would suffice as long as participants could access it online. We would vastly prefer a free version, with the plan to upgrade to a paid license if we need to continue this online format. Does any one have any suggestions? Thank you!
