1993 — 1994 |
Von Der Heydt, Rudiger |
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. |
Binocular Vision and Depth Perception @ Johns Hopkins University
This program of research aims at an understanding of the operational mechanisms in the cerebral cortex of primates which underlie stereoscopic depth perception. Experiments will be conducted in alert rhesus monkeys behaviorally trained to perform repeatedly a visual task, while single neuron activity will be recorded with one or more microelectrodes from striate and prestriate cortex. Stimuli will be presented stereoscopically on two color displays separately seen by the left and right eyes, and generated with a high-speed graphics system. The position of one (or both) eyes will be monitored continuously in order to control the monkey's direction of gaze. The principal objective is to obtain experimental evidence for or against the hypothesis that disparity-selective responses of cortical visual neurons are directly linked to stereoscopic depth perception, and to ascertain the significance of the different types of the neural disparity selectivity in the stereoscopic process. Three lines of investigation will be followed: First, experiments will be done to assess the responses of disparity selective neurons in visual areas V1, V2 and V3- V3A to solid figure and dynamic random-dot stereograms of different luminance contrast. Stereopsis is degraded or lost when viewing isoluminant stereopatterns: changes in the responses of stereoscopic neurons of monkey with stimuli of low luminance contrast would be a strong indication in favor of a direct role of these neurons in stereopsis. Moreover, the results of these experiments would provide information about which anatomo-physiological visual subsystem (magno- or parvo-cellular) neurons with stero properties are part. An associated series of experiments will be designed to investigate the mechanisms underlying the responses of cortical neurons to random-dot stereograms, that is of the mechanisms providing the substrate for the correct matching of corresponding elements of the images in the two eyes, a task that human subjects perform effortlessly and most accurately. Finally, I will attempt to assess the influences of attention and motivation on the neural responses of depth neurons in different cortical areas. The basic strategy of thee experiments will be to train the monkey to attend to the very stimulus that activates the cortical neuron under study, and to identify differences in the neuron's responses when that stimulus is or is not of behavioral relevance to the monkey.
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1995 — 1999 |
Von Der Heydt, Rudiger |
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. |
Neural Visual Coding--Image to Object Representation @ Johns Hopkins University
The broad aim for the next five years is to find a physiological approach to a central question of perception: the conception and representation of object& Experiments are proposed that will test the hypothesis of temporary (episodic) object representations in vision which are thought to be the intermediate stage between the image processing in visual cortex and the processes of object recognition and memory. The experiments are aimed at distinguishing between several alternative theories on the nature of such representations. Central to the project is the "binding problem", i.e., the question of how the system associates the features, attributes, or parts that belong to one object when several objects are present in a scene, in which form and for how long it represents this information, how it retrieves information from previous moments in the case of moving or changing objects, and how it keeps track of object identity. Answers to these questions are important for understanding perception and consciousness, and the function of the cerebral cortex in general. Specifically, they will contribute to a better understanding of visual disorders of central origin. A new behavioral paradigm and new visual test displays will be used in combination with multi-electrode extracellular neuron recordings to study the formation and decay of object representations and their use in recognition and identification of objects. The emphasis will be on recordings from visual area V4 and the inferior temporal cortex Various methods of spike train analysis will be used to analyze the patterns of neuronal responses, with particular attention to temporal coherence within and between neurons. Current theories of image segmentation, feature binding, and object representation will be evaluated, and new models developed, on the basis of the results.
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1999 — 2002 |
Von Der Heydt, Rudiger |
P01Activity Code Description: For the support of a broadly based, multidisciplinary, often long-term research program which has a specific major objective or a basic theme. A program project generally involves the organized efforts of relatively large groups, members of which are conducting research projects designed to elucidate the various aspects or components of this objective. Each research project is usually under the leadership of an established investigator. The grant can provide support for certain basic resources used by these groups in the program, including clinical components, the sharing of which facilitates the total research effort. A program project is directed toward a range of problems having a central research focus, in contrast to the usually narrower thrust of the traditional research project. Each project supported through this mechanism should contribute or be directly related to the common theme of the total research effort. These scientifically meritorious projects should demonstrate an essential element of unity and interdependence, i.e., a system of research activities and projects directed toward a well-defined research program goal. |
Neural Mechanisms of Three Dimensional Shape Perception in Visual Cortex @ Johns Hopkins University
Perception of three-dimensional (3D) objects is robust and stable, despite fragmentary and discontinuous sensory information. This is especially true for vision which is based only on 2D images. The visual system infers the depth of objects form binocular disparity and other, monocular, depth cues, such as motion parallax, perspective, shading, and occlusion. None of these cues is constantly available, and most of them are ambiguous. While disparity selectivity of cortical neurons is well documented, little is known about the processing in primate visual cortex of the monocular depth cues and the mechanisms of cue combination. The stability of perception suggests the existence of cortical depth representations that are cue invariant. The aim of this research is to determine (a) how elementary 3D features are represented in the visual cortex, (b) how different monocular and binocular cues contribute to this representation, and (c) how information from different cues is combined, especially in situations of ambiguity and conflict. The proposed approach is to study, for the same 3D objects and display conditions, (1) depth perception in human and monkey subjects, and (2) the neuronal activity in cortical areas V1, V2, and V4, of the awake, fixating monkey.
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2000 — 2011 |
Von Der Heydt, Rudiger |
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. |
Neural Visual Coding: Image to Object Representation @ Johns Hopkins University
DESCRIPTION (provided by applicant): Research is proposed to advance our understanding of the neural mechanisms of visual perceptual organization and their relation to selective attention. The long-term objective is to understand the interface between sensory representations and cognitive processes at the neural signal level. The proposed research focuses on the mechanisms of figure-ground organization as evident from the neural representation of border ownership, i.e., the assignment of contours to objects. The general method is single-cell recording from the visual cortex of awake behaving macaques. Three broad aims have been identified for the next five years. The first aim is to provide quantitative descriptions of the spatial integration mechanisms of border ownership selective V2 neurons. Previous studies have shown that these mechanisms extend far beyond the classical receptive field of the neurons. Two methods with factorial design will be applied. These methods allow to measure nonlinear interactions of the extra-classical regions with the classical receptive field as well as interactions between extra-classical regions. The two methods are complementary. One uses fragmentation of figures, the other uses occlusion of critical features. The second aim is to study persistence of figure-ground organization in the visual cortex. Experiments are proposed to (1) determine the influence of the type of figure-ground cue and its duration on the subsequent persistence of border ownership signals, (2) determine whether the persistence depends on attention being directed to the figure, and (3) whether border ownership signals persist across eye movements and stimulus movements. The third aim is to study the role of the neural organization mechanisms in object-based selective attention. Building on previous results showing that V2 neurons combine border ownership coding with the influence of volitional selective attention, new experiments will test visual conditions in which an object is partially occluded, so that only two unconnected portions of it remain visible. The results will show whether the border ownership mechanisms can link features across the gap, and whether object-based attention can do so. The proposed research will help to clarify the basis of selective attention which is important for understanding both normal and impaired vision. Although the proposal is focused on vision, the research will help to identify the sensory-cognitive interface also in other modalities. The insight gained from this project will contribute to the understanding of the basis of cognitive disorders such as dyslexia. PUBLIC HEALTH RELEVANCE Selective attention is perhaps the most important function in vision. We can choose to process the words in one line of text and ignore all others, which enables us to read. But sometimes we do not see things that are right in front of our eyes-the cause of many traffic accidents. Dyslexic children cannot detect the difference between strings of letters that others can easily see. The goal of the proposed research is to understand a process in the brain that dissects images into objects before objects are recognized, providing an internal representation from which attention can select.
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