Erich E. Sutter - US grants

This research plan includes two projects based on the same methodology: 1) Oculo-Encepalographic Communication (OEC). This project will establish a new method of communication and environmental contorl by means of the visual evoked potential. Information is communicated by visual fixation of one out of a number of flickering visual targets. The selected target is identified from the observer's evoked response which is derived from a pair of scalp electrodes. A transportable experimental system has been constructed for evaluation of the concept with communicatively disable persons. Tests revealed possibilities of significant improvement in preformance through additional research not included in the orginal proposal. We propose to study: a. Use of less conspicuous motion stimuli for target modulation. b. Effects of light adaptation on various response componets. c. Improvement of performance through implantation of electrodes (animal study). 2) Objective perimetry and light adaptation tests for medical diagnostics. Preliminary experiments have shown that the multi-input systems analysis techniques developed for the OEC project can be used for ERG and VER perimetry. Such objective perimetry techniques are desirable clinical tools which have been sought in vain by many investigators. Bases on the first successful ERG and VER perimetry data, a research plan is proposed which will result in viable clinical procedures. It includes: a) Optimization of stimulus parameters for extraction of specific local response components. b) Separate measure of spatial distributions of rod and cone responses. c) Evaluation of the diagnostic potential of the techniques with selected patients. Psychophysically measured glare recovery is a power clinical stress test. Presently, there is no objective test available for the clinic. A modified version of the OEC systems analysis technique can be used to pursue the time course of dark adaptation and glare recovery processes in the ERG and VER. Its potential as an objective diagnostic tool will be investigated.

This research plan includes two projects based on the same methodology: 1) Oculo-Encepalographic Communication (OEC). This project will establish a new method of communication and environmental contorl by means of the visual evoked potential. Information is communicated by visual fixation of one out of a number of flickering visual targets. The selected target is identified from the observer's evoked response which is derived from a pair of scalp electrodes. A transportable experimental system has been constructed for evaluation of the concept with communicatively disable persons. Tests revealed possibilities of significant improvement in preformance through additional research not included in the orginal proposal. We propose to study: a. Use of less conspicuous motion stimuli for target modulation. b. Effects of light adaptation on various response componets. c. Improvement of performance through implantation of electrodes (animal study). 2) Objective perimetry and light adaptation tests for medical diagnostics. Preliminary experiments have shown that the multi-input systems analysis techniques developed for the OEC project can be used for ERG and VER perimetry. Such objective perimetry techniques are desirable clinical tools which have been sought in vain by many investigators. Bases on the first successful ERG and VER perimetry data, a research plan is proposed which will result in viable clinical procedures. It includes: a) Optimization of stimulus parameters for extraction of specific local response components. b) Separate measure of spatial distributions of rod and cone responses. c) Evaluation of the diagnostic potential of the techniques with selected patients. Psychophysically measured glare recovery is a power clinical stress test. Presently, there is no objective test available for the clinic. A modified version of the OEC systems analysis technique can be used to pursue the time course of dark adaptation and glare recovery processes in the ERG and VER. Its potential as an objective diagnostic tool will be investigated.

The field topography of evoked potentials is the dependent of the responses on the location of a small stimulus in the visual field. Field topographies are derived with a method of simultaneous stimulation of a large number of locations and extraction of the local responses from a single response signal. The techniques for such studies have been developed and tested. Goal 1: Determination of the field topography of the luminance and pattern ERGs and their components. Correlation of these topographies with densities of retinal receptors and ganglion cells. Inter-subject differences will be studied to establish a baseline for a clinical evaluation. Goal 2: Development of an objective test of local retinal function for the purpose of screening, diagnosis and monitoring of patients. The field plots will be derived from patients with specific etiologies (glaucoma, ocular hypertension, maculopathy). The plots will be compared with fundus images to establish the exact location of retinal areas with abnormal ERG responses. ERG fields will be compared with psychophysical fields to assess their sensitivity in the detection of local pathological changes. Goal 3: Identification and characterization of ERG components from different retinal layers. This will be achieved with different modes of pattern stimulation and techniques of nonlinear systems analysis. Goal 4: Identification of VEP components from different visual areas of cortex. Functional characterization of their sources on the basis of nonlinear systems analysis. The field topography of the VEP is very complex due to the convoluted cortical anatomy. For each stimulus location, the relative contributions to the response from various cortical sources are different. A principal component analysis (SVD) will be applied to the responses at locations of comparable eccentricity in the visual field, to determine the subspace spanned by the components from different sources. The kernel structure of the nonlinear responses will be used to identify and characterize the components within this subspace. The invariance of the components between subjects will be tested to confirm the decomposition.

Long-range Goal: The project will lay foundation for future applications of a new and powerful functional imaging techniques for the detection and study of retinal dysfunction in man. The proposed studies will contribute significantly to establishing the connection between components of the ERG response in man and retinal mechanisms known from electrophysiological studies in animal models. During the previous project period the concept of functional imaging by means of multi-input nonlinear system analysis has been successfully tested in several projects and numerous pilot studies. A new methodology of source identification has evolved that will now be used to isolate and characterize signal components, particularly those from the inner retina. Nonlinearities in retinal processing which are primarily due to adaptive mechanisms will be used to discriminate signal sources. Their topographic distribution will then be compared with known anatomical properties for identification of the sources. The project will resolve standing controversies surrounding the pattern ERG and the oscillatory potentials and pave the way to early detection and characterization of glaucomatous damage. Specific aims are: 1. Discrimination of ERG components from pre- and post-receptoral mechanisms in the photopic ERG. Determination of the dynamics of post- receptoral adaptation. 2. Identification of ERG components from the proximal retina by means of the topographic distribution of their nonlinear characteristics. Study of pathological changes of these components in glaucoma patients. 3. Localization and characterization of slow adaptive mechanisms that are observed at mesopic levels and appear to be rod mediated. 4. Test of the hypothesis that changes in proximal components of the ERG (particularly latency increases in the pattern electroretinogram and the oscillatory potentials) toward the center are attributable to adaptation pooling. 5. Analysis of spatial extent and dynamics of long-rang spatial adaptation.

vision; biomedical equipment resource; biomedical facility; bioengineering /biomedical engineering;

[unreadable] DESCRIPTION (provided by applicant): The goal of this project is to test a model of top-down visual processing by noninvasive means in alert human observers. According to this model, the CNS actively explores the visual input, interacting with it through its endogenous activity. The interactions result in a temporal encoding of visual information that will be called visually modulated endogenous activity (VMEA). This response component does not need to correlate directly with abrupt changes in stimulus features and therefore eludes the commonly used techniques of stimulus-locked averaging. The existence of this component can be predicted in any system where the input interacts nonlinearly with fast endogenous processes and has been demonstrated in our pilot study using unconventional analysis tools. It shares many properties with the stimulus dependent synchronized high frequency oscillations found in animal studies. The method used in this study demodulates the endogenous carrier by means of nonlinear operations to retrieve its visual content. One of our aims is to optimize the stimulation and demodulation technique for the problem at hand. Other aims are to investigate [unreadable] the characteristics of the VMEA component and the role it may play in human visual perception. Specifically, we will study its dependence on the attentional state of the subject. We will investigate its dependence on stimulus geometry and color and we will compare the VMEA responses to random patterns with those to meaningful images with similar brightness contrast distributions. [unreadable] [unreadable]