Contrast (vision)

About: Contrast (vision) is a research topic. Over the lifetime, 10379 publications have been published within this topic receiving 221480 citations.

Illusory contours and cortical neuron responses

Abstract: Figures in which human observers perceive "illusory contours" were found to evoke responses in cells of area 18 in the visual cortex of alert monkeys. The cells responded as if the contours were formed by real lines or edges. Modifications that weakened the perception of contours also reduced the neuronal responses. In contrast, cells in area 17 were apparently unable to "see" these contours.

Neural dynamics of form perception: boundary completion, illusory figures, and neon color spreading.

Abstract: A real-time visual processing theory is used to analyse real and illusory contour formation, contour and brightness interactions, neon color spreading, complementary color induction, and filling-in of discounted illuminants and scotomas The theory also physically interprets and generalizes Land's retinex theory These phenomena are traced to adaptive processes that overcome limitations of visual uptake to synthesize informative visual representations of the external world Two parallel contour sensitive processes interact to generate the theory's brightness, color, and form estimates A boundary contour process is sensitive to orientation and amount of contrast but not to direction of contrast in scenic edges It synthesizes boundaries sensitive to the global configuration of scenic elements A feature contour process is insensitive to orientation but sensitive to both amount of contrast and to direction of contrast in scenic edges It triggers a diffusive filling-in of featural quality within perceptual domains whose boundaries are determined by completed boundary contours The boundary contour process is hypothesized to include cortical interactions initiated by hypercolumns in Area 17 of the visual cortex The feature contour process is hypothesized to include cortical interactions initiated by the cytochrome oxydase staining blobs in Area 17 Relevant data from striate and prestriate visual cortex, including data that support two predictions, are reviewed Implications for other perceptual theories and axioms of geometry are discussed

Automated Static Perimetry

Abstract: PART ONE: BASICS 1. Introductory Concepts Anatomy and Function of the Eye Visual Field Correspondence of the Retina and Visual Field Boundaries of the Visual Field 2. Basis of Quantitative Perimetry Visual Characteristics Within the Visual Field Units of Light Intensity Threshold Sensitivity in Terms of Stimulus Intensity Frequency-of-Seeing Curve and Short-Term Fluctuations Long-term Fluctuation Subjective Stimulus Brightness Background Intensity Contrast Sensitivity and Veiling Glare Refractive Error and Retinal Blur Stimulus Size and Spatial Summation Temporal Summation and Stimulus Deviation Learning Effects Fatigue Effects Kinetic and Static Stimuli Chromatic Perimetry Other Types of Perimetry 3. Topographic Classification of Visual Field Defects Anatomical Basis Prechiasmal defects Postchiasmal Defects Stato-kinetic dissociation (Riddoch Phenomenon) 4. Visual Field Loss in Glaucoma Local and diffuse loss Anatomic basis of nerve fiber bundle pattern Hemifield asymmetry and nasal steps Point of Fixation Generalized Depression Summary and Examples PART TWO: OFFICE PERIMETRY 5. Clinical Static Perimetry Basic Goals Mainstream Perimetric Protocols The Original, Classic Central Static Threshold Test New Thresholding Algorithms Determining Test Reliability Current Thresholding Algorithms: Summary Suprathreshold Tests Structuring the Test Conditions 6. The Single Field Printout Basic Identification Reliability Parameters Questions and test time Raw Test Results Total Deviation (From Normal Values For Age) Pattern Deviation (Localized Loss) Global Indices Plain Language Analysis 7. Interpretation of a Single Field Reliability Is The Field Abnormal? How Advanced Is The Disease? Artifacts 8. Selection of Automated Tests Glaucoma Diagnosis in the Office Population Screening for Glaucoma Following the Patient with Glaucoma Neurologic Conditions Retinal Diseases Blepharoptosis Driving Qualification Visual Impairment and Disability Programs That are Obsolete or Rarely Used 9. Follow-Up Examinations Establishing a Baseline Follow-up Visual Field Examinations An Overview Change Analysis Printout Pointwise Changes Interpretation Conclusion 10. Alternate and Supplemental Techniques Amsler Grid Confrontation Techniques PART THREE: TECHNIQUE 11. Administering the Visual Field Test Patient's Perception of the Test Perimetrist's Task Instructing the Patient About the Test Positioning the Patient at the Perimeter Corrective Lenses Monitoring and Modifying the Test After the Test APPENDICES Appendix A - Abbreviations Appendix B - Characteristics and Comparison of the HFA-2 Humphrey Perimeter to the HFA-1 Model Appendix C - Glossary INDEX

Visual risk factors for falls in older people.

Abstract: OBJECTIVES: To determine the tests most predictive of falls in community-dwelling older people from a range of visual screening tests (high and low contrast visual acuity, edge contrast sensitivity, depth perception, and visual field size). To determine whether one or more of these visual measures, in association with measures of sensation, strength, reaction time, and balance, can accurately predict falls in this group. DESIGN: Prospective cohort study of 12 months duration. SETTING: Falls and Balance Laboratory, Prince of Wales Medical Research Institute. PARTICIPANTS: 156 community-dwelling men and women age 63 to 90 (mean age 76.5, standard deviation = 5.1). MEASUREMENTS: Screening tests of vision, sensation, strength, reaction time and balance, falls. RESULTS: Of the 148 subjects available at follow-up, 64 (43.2%) reported falling, with 32 (21.7%) reporting multiple falls. Multiple fallers had decreased vision, as indicated by all visual tests, with impaired depth perception, contrast sensitivity, and low-contrast visual acuity being the strongest risk factors. Subjects with good vision in both eyes had the lowest rate of falls, whereas those with good vision in one eye and only moderate or poor vision in the other eye had elevated falling rates-equivalent to those with moderate or poor vision in both eyes. Discriminant analysis revealed that impaired depth perception, slow reaction time, and increased body sway on a compliant surface were significantly and independently associated with falls. These variables correctly classified 76% of the cases, with similar sensitivity and specificity. CONCLUSION: The study findings indicate that impaired vision is an important and independent risk factor for falls. Adequate depth perception and distant-edge-contrast sensitivity, in particular, appear to be important for maintaining balance and detecting and avoiding hazards in the environment.