Preeti Verghese - US grants

In recent years, there has been an extraordinary number of physiological and psychophysical studies of the primate motion system, and endeavor encouraged by the National Plan for Vision Research 1994-1998 (p.273- 275). This work has established the main characteristics of local motion processing units. To be useful, the responses of these local motion units must be combined over space and time to guide locomotion and to aid object recognition. This proposal will examine how these local responses re combined. An object moving within a complex background is readily visible, and easily identifiable, despite occluding surfaces and the surrounding motion of other features. This observation suggests that the local motion units are organized along the slowly-changing paths taken by real objects, where rapid changes in direction are improbable. First, human psychophysical experiments will demonstrate increased visibility for targets that fall on a common motion path. Subsequent measurements will examine how this increased visibility is accomplished, and what information is lot by pooling the local motion signals into a network. These studies will improve basic scientific knowledge on human motion processing. Motion processing is critical for mobility in a structured environment. Thus, there results may assist in the design of devices and training procedures that enhanced mobility in individuals suffering from low vision.

A person effortlessly identifies objects of interest in cluttered scenes, the keys on a cluttered desktop or the stuffed elephant in a crowded toy chest. In a cluttered scene, parts of one object may occlude another, so the edges that belong to one object are obscured by the edges of occluding objects. How does a person so effortlessly sort out such a complex array of overlapping objects? With NSF support Dr. Preeti Verghese will explore the relevant process in perception, processes that sort out complex arrays and identify the objects therein.
Broader impacts of Dr. Verghese's work will include a better understanding of the problem of amblyopia. The capacity to correctly perceive objects is impaired in amblyopia, which occurs as a result of abnormal visual development. Amblyopes have great difficulty tracing the outline of an object, for example, especially in a cluttered background. Basic research to understand intact perception of cluttered scenes will shed light on the abnormalities associated with amblyopia.

Humans have an amazing ability to pick out an object of interest from a cluttered scene. This can be a difficult task; for example, many animals, from caterpillars to tigers, have coloration and markings that allow them to blend into their environments. However, context and knowledge can help reveal the hidden form, and are particularly useful in selecting relevant information when a person searches for a target.

With support from the National Science Foundation, Dr. Verghese will examine the detection of two kinds of targets in cluttered backgrounds--those with smooth contours in static scenes and those with smooth motion trajectories in dynamic scenes. Previous studies have shown that humans are extremely good at finding smooth contours and smooth motion paths even when visibility is very poor. The usefulness of these aspects for identifying forms in visual input has presumably been learned by experience: Contours and motion paths in real-world scenes tend to change direction slowly and smoothly. Dr. Verghese will examine how the visual system comes, over time and experience, to be able to exploit this smoothness property for both static and moving paths. This will be done by asking observers to report the location and direction of a path hidden in a background at various distances from a starting point, and at various times after display onset. Both choice responses and eye movements will be compared to predictive models to help reveal how evidence for the extended path accumulates. These studies will shed light on how humans predict the future path of moving targets, and how they integrate local contour fragments into full contours that define the boundaries of objects. Path and boundary perception are fundamental visual processes that may have important implications for perceptual training and for machine vision. The project will also make special efforts to draw high school and college students into the scientific work.

When we interact with our surroundings we are often looking at or reaching for an object of interest that is embedded in the clutter of daily life. Successful interaction with our surroundings requires that several processes work in concert. These include image-related factors, such as, how the target of our reaching differs from its surroundings, visual processes that organize the scene into potential targets and background, and cognitive factors such as task demands and prior knowledge of target. With funding from the National Science Foundation, Dr. Preeti Verghese and her colleagues are investigating how all of these processes unfold over time, and how they interact to select a target on a textured background. Their research uses psychophysics, as well as high-density electroencephalography (EEG) combined with a process that localizes the cortical sources of the scalp potentials to determine the neural populations that implement these processes. The two aims address important questions about the interaction of selective attention and segmentation processes: When attention is directed to a target, how do the surrounding context and task requirements influence how efficiently the target is selected? What is the time course of this interaction: How does evidence for the target evolve over time, and how do attention and task demands influence the way in which a target is segmented from the background?

This study aims to understand the neural underpinnings of target selection in the real world. As such it has relevance to activities of daily life. It is also relevant to clinical populations with people who have difficulty with target selection. These include people with damage to parts of the visual cortex due to stroke, injury, or tumors that result in a diminished awareness of objects that are represented by the affected parts of the cortex. This visual neglect is particularly acute in the presence of other objects in the visual field. Training is also a strong component of this research program. This research project provides research opportunities for high school and undergraduate students to gain exposure to science as summer interns. Because the research is multidisciplinary, postdoctoral fellows are having the opportunity to train in research areas that complement their doctoral research.

DESCRIPTION (provided by applicant): Age-related macular degeneration affects central vision and impairs high acuity visual function. Individuals with AMD complain about difficulty with everyday tasks such as reading, recognizing faces and watching television. More recent studies report difficulty with eye-hand coordination and grasping, consistent with data showing that the majority of individuals with AMD have little depth perception. Stereopsis can be impaired when the two eyes have very disparate patterns of vision loss, particularly when the stronger eye determines binocular gaze direction, without regard to the functional status of the corresponding fixation location in the other eye. Loss of depth perception not only impacts tasks requiring eye hand coordination, but it can have serious consequences for mobility and obstacle avoidance. In this proposal we examine the potential to restore stereopsis in individuals with AMD, by encouraging individuals to use fixation loci in the two eyes that have similar function. We start by examining the potential for depth perception in Aim 1. This requires mapping the regions of residual function in the two eyes to determine if there are corresponding points in the periphery that can subserve depth perception. In Aim 2 we determine whether observers are able to combine information from the two eyes (a necessary prerequisite for stereopsis) and whether they have any degree of depth perception. In Aim 3 we test the hypothesis that individuals with AMD are able to use different fixation loci for different tasks. We take two approaches to encourage observers to use retinal loci that are functionally equivalent and in corresponding locations in the two eyes, so they can provide a substrate for depth perception. We first artificially equate the pattern of vision loss in the two eyes and allo observers to practice coordinated eye movements. We then determine whether they use these corresponding fixation locations in an eye-hand coordination task that benefits from depth information. If indeed the choice of fixation location is task- dependent, we expect that practice with these two tasks will improve binocular correspondence and potentially lead to a recovery of stereopsis.

? DESCRIPTION (provided by applicant): We propose an Institutional Training Grant at the Smith-Kettlewell Eye Research Institute (SKERI) to provide postdoctoral training in basic and clinical science relevant to translational vision research and rehabilitation. Thirteen faculty members whose expertise spans the areas of spatial and binocular vision, eye movements, strabismus, central vision loss, low vision and blindness rehabilitation, computer vision and assistive technology will train postdoctoral fellows seeking to specialize in translational vision research and rehabilitation. Research training goals will be accomplished through intensively supervised research projects, frequent and wide-ranging seminars, journal clubs and colloquia, as well as supervised research performance, proposal development and grant writing. Because the vast majority of SKERI Faculty are full-time researchers with no teaching duties and small laboratories, the Fellows experience a great deal of direct interaction with their sponsors. In addition, the Fellows have available to them many opportunities for interaction with the rest of the Faculty, which include basic, clinician and rehabilitation researchers. These interactions are facilitated by the group all being housed within the same building and all working in clinically relevant vision research. The Faculty-Fellow interactions represent all areas of the research process: proposal, critique, performance, and communication of findings through the writing of papers and preparation of presentations, as well as participation in scientific and ethics seminars. Importantly, Fellows are also in frequent contact with each other through organized events, adjacent open work-spaces, and the numerous collaborations among Faculty. The Fellowship program forms a critical component of the research vitality and capacity of SKERI. Because SKERI is not a degree-granting institution, its investigators do not typically have graduate students. It is widely appreciated within the Institute that Fellows bring in new ideas and techniques to the preceptors' laboratories. The process of training Fellows encourages Faculty to challenge old assumptions, to develop clear and concise descriptions of why a given research activity is of significance, and to expand the range of approaches to research problems. The T32 Program will significantly augment SKERI's internally funded Rachel C. Atkinson Fellowship, C.V. Starr Scholarship Program, and individual Fellowship awards from other sources to yield an overall program size of approximately 6-7 post-doctoral fellows.

ABSTRACT Age-related macular degeneration affects the central part of the visual field, which provides high acuity visual function and serves as the reference point for eye movements. Thus difficulties with reading and with eye movements are common complaints. Extensive research effort has been invested in understanding the causes of reading difficulties in individuals with vision loss, leading to the development of optical devices and assistive technology to alleviate the problem. However, much less attention has been paid to the obstacles central field loss poses to tasks of daily living. Individuals complain about difficulty shopping for groceries, finding items at home, following moving targets, performing eye-hand coordination tasks and navigating. Our goal is to develop research methods to help patients with central vision loss learn to use their remaining vision effectively. We believe that three factors underlie the difficulties that individuals with AMD confront while performing everyday tasks. Firstly, most are unaware of the location of the region of vision loss (scotoma) and are therefore unaware of objects obscured by the scotoma. To address this issue Aim 1 will investigate methods that teach scotoma awareness and direct eye movements towards the scotoma to locate static objects that would otherwise go undetected. Secondly, while individuals adopt a peripheral retinal locus when the fovea is affected, the shift of the eye-movement reference to this new locus takes much longer. Thus they have difficulty directing their gaze to objects of interest and tracking moving objects, particularly those moving toward them, in depth. Aim 2 will use training tasks that help patients direct their PRLs to acquire and track targets whose position and direction of motion are unpredictable, and to become aware that their scotoma extends in depth, so that they can keep track of oncoming objects such as cars and bicyclists. Finally, stereopsis can be impaired when the two eyes have very disparate patterns of vision loss, particularly when the stronger eye determines binocular gaze direction, without regard to the functional status of the corresponding fixation location in the other eye. To address this issue, Aim 3 will evaluate the potential for coarse stereopsis in the peripheral part of the visual field to improve eye hand coordination in near space.