Chapter 4 Visual Sensory System.docx

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Western University
Management and Organizational Studies
Management and Organizational Studies 3305A/B
Suzanne Kearns

Lecture 2: Chapter 4 VISUAL SENSORY SYSTEM September 18, 2013  Light could be meaningless… it depends how you process/interpret it  Experience allows us to interpret and define what the light is  Everything we see is converted by the brain…  interpreted in different way o What is “real”  how does the brain interpret it to “make sense” THE STIMULUS  Electromagnetic energy  Approximately 400nm – 700nm 1 th o Only / 17 of the total spectrum o 700 = red light to us  Qualities of light o Hue (colour) o Brightness (dark/light) o Saturation (take colour to light) QUANTIFYING THE STIMULUS  2 concepts of brightness o Illuminance: amount of light that actually reaches an object to be viewed o Luminance: amount of light reflected off of an object  ( ) o Used in aircraft design o Need to be able to see the aircraft THE HUMAN RECEPTOR SYSTEM  Electromagnetic energy [TRANSFORMED] into electrochemical neural energy by the EYE CONE AND ROD VISION  Cones: visual receptors that mediate high acuity colour vision in good lighting  Rods: visual receptors that mediate achromatic low acuity vision under dim light o Night, B&W  Scotopic vision: night vision using only rods  Photopic vision: sufficient light to activate rods & cones o Cones are dominant Cones Rods Location  Middle region of retina (fovea) exclusively  Outside fovea mostly Acuity  Great acuity  Less Motion sensitivity  Moderate  High (good for peripheral)  More Sensitivity  Less o At night, only rods function o 15 min. to adapt Colour sensitivity  Yes  None Adaptation  Hypersensitive, with little stimulation  Rapidly lose sensitivity o Long time to regain Differential wavelength sensitivity  Sensitive to all visible wave lengths  Insensitive to long wavelength (red)  Differences put great limitations on our visual sensory processing  Human-machine systems must be designed with limitations in mind BLIND SPOT  Next to the fovea is an area where there are neither rods nor cones o Where the optic nerve exits the eye to connect to the brain o Called the “blind spot”  Brain automatically fills in the blind spot  try to make sense out of it ACCOMMODATION  Accommodation: ability of the lens of the eye to focus the light rays on the retina o Visual acuity o High acuity  Allows us to see details  crucial in designing equipment o Muscles do the focusing  Near point: closest distance to which eyes can focus  Far point: near infinity for normal vision  How much space is our visual acuity? High acuity vision… $0.25 in size VISUALA CUITY  Types of acuity Vernier Are the two lines parallel? Landolt ring Is the gap detectable? Recognition What letter is presented? Minimum separable Are the objects connected?  Measurement of detail at 20 feet relative to distance normal observer can Snellen acuity resolve the sale detail (i.e. 20/20) o If someone needs to stand closer to see (ex. 20/10)  In human factors, we just need to have person to be able to see SENSORY PROCESSING LIMITATIONS READING PRINT  Most obviously, print should not be too fine  Font matters  Maximize contrast  Dark text on light background (negative contrast) BETTER than light text on dark background (positive contrast) COLOUR SENSATION  Colour sensation o Detect different colours o Variables  Low levels of illumination = low colour sensation  Gender: 7% males colour deficient  Negative after-image (what happens when you look at colour for long period of time) o Describes greater intensity of certain colours viewed after prolonged viewing of other colours  Design for monochrome readability first (i.e. black and white)  Use colour as a means to enhance information o Example: traffic lights use colour and location CONTRAST SENSITIVITY  Refers to the sensitivity of the visual system  Its ability to detect differences in contrast  How much space between 2 objects to see
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