School of Mechanical, Industrial, and Manufacturing Engineering The Visual System and Visual Performance

School of Mechanical, Industrial, and Manufacturing Engineering 2 Photometry: Electromagnetic Spectrum

School of Mechanical, Industrial, and Manufacturing Engineering 3 Photometry: Basic Concepts Source Reflective surface Observer Luminous flux - lumens Illuminance - lux - foot-candles Luminance - foot-lamberts - milli-Lamberts

School of Mechanical, Industrial, and Manufacturing Engineering 4 Photometry: Concepts and Units ● Luminous intensity ● Power of light emitted by source in particular direction ● Units: candelas (cd) ● Candle emits ~1cd ● Luminous flux ● Power of light perceived by human eye ● Units: lumens (lm) ● Illuminance ● Luminous flux reaching a surface per unit area ● Units – Lux (lx) = lm / m 2 – Foot-candles (fc) = lm / ft 2 ● Luminance ● Luminous flux leaving (reflected from) a surface ● Units – Foot Lamberts (fL): = lm / ft 2 – “nits” = cd / m 2 ● Contrast: luminance ratio ● Reflectance: % reflected ● Brightness: perception

School of Mechanical, Industrial, and Manufacturing Engineering 5 Luminance Note: 1 foot-Lambert (ft-L) = mL, so 1 ft-L ~ 1 mL.

School of Mechanical, Industrial, and Manufacturing Engineering 6 Luminance (2) ● Threshold of detectability 1 x mL ● Threshold of pain 3 x 10 4 mL ● Limits to discriminability levels

School of Mechanical, Industrial, and Manufacturing Engineering 7 Anatomy and Physiology: The Eye Illustration by Mark Ericksen, St. Luke’s Cataract and Laser Center, StLukesEye.com

School of Mechanical, Industrial, and Manufacturing Engineering 8 Anatomy and Physiology: The Eye (2) ● Cornea ● Protection ● Focusing ● Sclera: white of the eye ● Aqueous Humor ● Shape ● Nutrition ● Iris ● Light control ● Focusing ● Lens ● Focusing (ciliary muscles) ● Accommodation ● Vitreous Humor ● Shape ● Choroid: vascular layer, connective tissue between sclera and retina ● Retina ● Rods: black & white, night vision ● Cones: color, day vision ● Fovea: sharpest vision (concentration of cones) ● Macula: area around fovea ● Optic Nerve ● Nerve signals to brain ● Optic Disk: blind spot ● Eye Muscles ● Eye movement ● Convergence

School of Mechanical, Industrial, and Manufacturing Engineering 9 Common Vision Conditions ● Myopia ● Hyperopia ● Presbyopia

School of Mechanical, Industrial, and Manufacturing Engineering 10 Visual Performance ● Brightness ● Visual Angle ● Visual Acuity ● Color ● Visual Field

School of Mechanical, Industrial, and Manufacturing Engineering 11 Brightness ● Relative amount of light reflected from an object produces a sensation of lightness or brightness. ● Brightness is related to the luminance of light as well as a subjective response to color

School of Mechanical, Industrial, and Manufacturing Engineering 12 Visual Angle (minutes of arc)

School of Mechanical, Industrial, and Manufacturing Engineering 13 Visual Angle of Familiar Objects ObjectDistanceVisual Angle Sun 93,000,000 mi30’ Moon240,000 mi30’ Quarterarm’s length2° Quarter90 yd1’ Quarter3 mi1” Lowercase pica 1 typereading distance13’ 1 a 12-point font

School of Mechanical, Industrial, and Manufacturing Engineering 14 Cumulative Probability of Detection

School of Mechanical, Industrial, and Manufacturing Engineering 15 Visual Acuity ● Ability to resolve detail ● Often, inverse of smallest visual angle (in minutes) that can be resolved ● e.g., Acuity = 1 ● Observer can resolve/detect a feature of 1 minute VA

School of Mechanical, Industrial, and Manufacturing Engineering 16 Variation in Visual Performance Across the Retina

School of Mechanical, Industrial, and Manufacturing Engineering 17 Minimum Separable Acuity ● Also called gap resolution ● Smallest VA eye can detect between parts of a target (visual object).

School of Mechanical, Industrial, and Manufacturing Engineering 18 Minimum Separable Acuity as Function of Contrast

School of Mechanical, Industrial, and Manufacturing Engineering 19 Minimum Perceptible Acuity ● Also called spot detection. ● Eye’s ability to detect smallest possible target.

School of Mechanical, Industrial, and Manufacturing Engineering 20 Minimum Perceptible Acuity as Function of Contrast and Background Luminance

School of Mechanical, Industrial, and Manufacturing Engineering 21 Vernier Acuity ● Smallest lateral displacement of one line from another that can be detected.

School of Mechanical, Industrial, and Manufacturing Engineering 22 Vernier Acuity as Function of Background Luminance

School of Mechanical, Industrial, and Manufacturing Engineering 23 Landolt Ring / Landolt C Image source:

School of Mechanical, Industrial, and Manufacturing Engineering 24 Color ● Attributes ● hue: red, green, blue … ● saturation: vividness of hue ● brightness: luminance ● Relative discrimination ● thousands of distinct colors ● Absolute discrimination ● 24 distinct colors ● recommended: 9

School of Mechanical, Industrial, and Manufacturing Engineering 25 Visual Field

School of Mechanical, Industrial, and Manufacturing Engineering 26 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

School of Mechanical, Industrial, and Manufacturing Engineering 27 Other Factors Affecting Visual Performance ● Contrast: optimum level exists ● Illumination: optimum level exists ● Time: positive relationship ● Luminance Ratio: see contrast

School of Mechanical, Industrial, and Manufacturing Engineering 28 Other Factors Affecting Visual Performance (2) ● Glare: negative relationship ● Movement: negative relationship ● Age: negative relationship ● Drugs: some drugs impair vision

School of Mechanical, Industrial, and Manufacturing Engineering 29 Other Vision Topics For Discussion ● Color Sensation (e.g, color deficiencies, color “blindness”) ● Night Vision (glare, age effects) ● Bottom-Up vs Top-Down Processing ● Eye Movement (pursuit vs. saccadic) ● Visual Search (serial search, expectancies, conspicuity) ● Signal Detection Theory (noise, signal, hit, miss, false alarm) ● Discrimination (JND)