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The Visual System and Visual Performance. The Visible Spectrum.

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Presentation on theme: "The Visual System and Visual Performance. The Visible Spectrum."— Presentation transcript:

1 The Visual System and Visual Performance

2 The Visible Spectrum

3 3 vision.ppt Anatomy of the Eye Illustration by Mark Ericksen, St. Luke’s Cataract and Laser Center, StLukesEye.com

4 4 vision.ppt The Eye (2) lCornea  Protection  Focusing lAqueous Humor  Shape  Nutrition lIris  Light control  Focusing

5 5 vision.ppt The Eye (3) lLens  Focusing  Accommodation lVitreous Humor  Shape lRetina  Rods: black & white, night vision  Cones: color, day vision  Fovea: sharpest vision (concentration of cones)

6 6 vision.ppt The Eye (4) lOptic Nerve  Nerve signals to brain  Optic Disk: blind spot lEye Muscles  Eye movement  Convergence

7 7 vision.ppt NEAR AND FARSIGHTED EYE

8 8 vision.ppt DENSITY OF RODS AND CONES

9 9 vision.ppt Visual Performance lBrightness lVisual Angle lVisual Acuity lColor lVisual Field

10 10 vision.ppt Brightness lRelative amount of light reflected from an object produces a sensation of lightness or brightness. lBrightness is related to the luminance of light as well as a subjective response to color

11 11 vision.ppt Luminous Intensity

12 12 vision.ppt Luminous Flux

13 13 vision.ppt Illuminance

14 14 vision.ppt Illuminance v. Luminance lIllumination/Illuminance: The amount of light striking any point on the inside surface of a sphere surrounding the light source (Luminous flux/unit area)  Foot candle: 1 lumen/square foot  Lux: 1 luman/square meter lLuminance: The amount of light per unit area leaving (reflected from) a surface  Foot Lamberts: 1 lumen/square foot  Candelas/square meeter

15 15 vision.ppt Luminance Note: 1 foot-Lambert (ft-L) = 0.929 mL, so 1 ft-L ~ 1 mL.

16 16 vision.ppt Luminance (2) lThreshold of detectability 1 x 10 -6 mL lThreshold of pain 3 x 10 4 mL lLimits to discriminability 3 - 4 levels

17 17 vision.ppt Lightness

18 18 vision.ppt Visual Angle (minutes of arc) Visual Angle = tan -1 H/D

19 19 vision.ppt Visual Angle of Familiar Objects ObjectDistanceVisual Angle Sun 93,000,000 mi30’ Moon240,000 mi30’ Quarterarm’s length2° Quarter90 yd1’ Quarter3 mi1” Lowercase pica typereading distance13’

20 20 vision.ppt Cumulative Probability of Detection

21 21 vision.ppt

22 22 vision.ppt Minimum Separable Acuity lAlso called gap resolution lSmallest space eye can detect between parts of a target (visual object).

23 23 vision.ppt Minimum Separable Acuity as Function of Contrast

24 24 vision.ppt Minimum Perceptible Acuity lAlso called spot detection. lEye’s ability to detect smallest possible target.

25 25 vision.ppt Minimum Perceptible Acuity as Function of Contrast and Background Luminance

26 26 vision.ppt Vernier Acuity lSmallest lateral displacement of one line from another that can be detected.

27 27 vision.ppt Vernier Acuity as Function of Background Luminance

28 28 vision.ppt Color lAttributes  hue: red, green, blue …  saturation: vividness of hue  brightness: luminance lRelative discrimination  thousands of distinct colors lAbsolute discrimination  24 distinct colors  recommended: 9

29 Visual Field

30 30 vision.ppt Visual Impairments Myopia :Nearsightedness Hyperopia :Farsightedness Presbyopia :Loss of accommodation Night Blindness :Reduced rod vision Color Blindness :Inability to discriminate Tunnel Vision : Reduced field of view

31 31 vision.ppt Other Factors Affecting Visual Performance lContrast: optimum level exists lIllumination: optimum level exists lTime: positive relationship lLuminance Ratio: see contrast

32 32 vision.ppt Other Factors Affecting Visual Performance (2) lGlare: negative relationship lMovement: negative relationship lAge: negative relationship lDrugs: some drugs impair vision

33 33 vision.ppt

34 34 vision.ppt

35 35 vision.ppt

36 36 vision.ppt

37 37 vision.ppt

38 38 vision.ppt

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