1. The Information Processing Model
A model for understanding human cognition.
from: Wickens, Lee, Liu, & Becker (2004) An Introduction to Human Factors Engineering. p. 122
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2. Assumptions in the IP Model
Each stage transforms data and takes some time
Sensory processing
visual, auditory, kinesthetic
quality and quantity of input depend on limits of senses
Short-term sensory store
temporary storage at the sensory channel
requires no conscious attention
Perceptual encoding
stimulus is assigned to single perceptual category (from LTM)
levels of complexity of perceptual decisions
absolute judgement (1 dimension)
loudness of a tone, crowd size
pattern recognition (2 or more dimensions)
medical diagnosis, Sherlock Holmes
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3. Assumptions in the IP Model
Stages (cont.)
Decision making
what to do with perceived information
critical point in information processing
Memory
Working memory (short-term memory)
Long-term memory
Response execution
calling up and releasing necessary muscle commands to perform actions
very complex
Feedback
monitoring the consequences of actions
not necessarily conscious
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4. Assumptions in the IP Model
Stages (cont.)
Attention
searchlight - which information source to monitor
resource of limited availability
Model not to be taken literally
Implies passivity; where are the goals?
Stages not sharply defined; overlap in time
Stages are not really "boxes" in the brain
Information flow may be right to left;
e.g., expectations can influence perceptions
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5. The Information Processing Model
The traditional driver for research and understanding.
A useful organization scheme.
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6. Sensory Register, Part I: The Visual Sensory System
How we see: "Light (electromagnetic radiation) is collected by the cornea and passes through the anterior chamber, then through the pupil, which is an aperture in the iris diaphragm, to the crystalline lens. The lens focuses the light by changing shape in a process called accommodation. The image passes through the vitreous humor in the posterior chamber and is projected onto the retina. The retina contains two kinds of photo receptors: rods, which are sensitive to dim light, and cones, which are used in bright light and convey color information. The central region of the retina, which provides the best visual acuity, is the fovea, which contains only cones. Information from the photoreceptors passes through the bipolar cells and ganglion cells (cells in the retina) before passing out of the eye via the optic nerve."[1]
[1] Coren, S., Ward, L., & Enns, J. (1999). Sensation and perception (5th ed.). Fort Worth :Harcourt Brace, p. 83.
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7. The Visual Receptor System (see chapter 4)
The lens
cornea – protective surface
pupil – opens (dilates) in darkness, closes (constricts) in light
accomodation: _______________________________
measured in diopters
The retina
cones: ___________________________
rods: ____________________________
fovea: ___________________________
acuity: ___________________________
scotopic vision: ______________________
photopic vision: ______________________
adaptation: _________________________
Accommodation - the lens changing to focus an image.
1 diopter = accommodation required to view an object at 1 meter.
cones: located primarily in the middle region of the retina; better at picking up fine detail (better acuity); better color sensitivity; more sensitive to glare in low light
rods: located primarily on the periphery of the retina; more sensitive (better in low light); “color blind”; more sensitive to motion
fovea: center of the eye; composed entirely of cones
acuity: smallest visual angle that can be detected (see table 4.2, pg 68)
scotopic vision: night vision, only rods operating
photopic vision: vision when illusion is sufficient to activate both rods and cones (mostly cones)
adaptation: the time it takes for rods to regain their sensitivity after exposure to light
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8. Example: driving at night
Specific hazards caused by:
Glare
Reduced contrast sensitivity
Loss of color vision
Particularly bad for older drivers due to:
Loss of contrast sensitivity due to age
Loss of accomodation
Glare is irrelevant light of high intensity. It has the effect of destroying the rod's sensitivity to low spatial frequencies.
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9. What affects Visibility?
Of print…
Good
Bad
BAD
item 1: too small (font size)
item 2: too light (contrast)
item 3: difficult fonts (e.g., spatial frequency)
item 4: polarity (light on dark) – what is “good” depends on environment, lighting, etc.
Bad
Bad
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10. What affects Visibility?
Characterizing and Measuring Light
Color
hue
pure wavelength
visible spectrum ~400 – 700 nm
saturation
amount of achromatic light mixed in
brightness
amplitude
Design considerations
use color as a secondary source of information
design for monochrome first
consider
simultaneous contrast
negative afterimage
. Know how to use color in displays. It should be used as a secondary source of information. Design for monochrome first. Simultaneous contrast and negative afterimage affect our perception of color.
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11. What affects Visibility?
Characterizing and Measuring Light (cont.)
Brightness measures (review)
luminous intensity, luminous flux
energy at the source, candela
illuminance
amount of energy striking an object, lux or foot-candles (fc)
luminance
amount of energy reflected from an object, foot-lambert (FL)
reflectance
ratio of the amount of light striking the object to the light reflected from the object,
illuminance
luminance
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12. What affects Visibility?
Characteristics of Visual Displays
Visual angle,
VA = tan-1(H/D)
VA = 3438H/D min
Example: reading ‘Good’ text from your notes page,
H = ______
D = ______
VA = ___________________________
For example, H = 0.25 in
D = 18 in
VA = tan-1(H/D) = tan-1(0.25/18) = ° = min.
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13. What affects Visibility?
Characteristics of Visual Displays (cont.)
Contrast,
Luminance of light areas, LL
Luminance of dark areas, LD
Contrast =
Spatial frequency
cycles of light and dark per degree of VA
Polarity
dark on light vs light on dark
(LL – LD)
(LL + LD)
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14. What affects Visibility?
Characteristics of Observers
Visual Acuity
Age
Contrast sensitivity
Night vision
Characteristics of Environment
Ambient light
e.g., daylight vs night, glare, etc.
Movement
Distractions
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15. Your turn …
Define system requirements for your project based on this understanding of the visual sensory system.
Typical statements could include:
The system must accommodate ____________________.
The system should allow for _______________________.
The system should include mechanisms that will _____________________.
Be careful not to start designing yet!
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