1 human information processing: chapters 4-9 n computer as a metaphor for human performance n misses...
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Human information processing:Chapters 4-9
Computer as a metaphor for human performance Misses role of emotion and distributed cognition
Receptors Perception
Long-term memory
Decision and response selection
Response execution
Controlled system
Workingmemory
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Visual sensory system
Perceptually relevant characteristics of light The receptor system: The eyeball Basic sensory limits of the receptor cells (rods and cones) Perceptual processing
• Depth perception• Visual search• Detection• Discrimination• Absolute judgement
Bottom-up and top-down processes combine to guide visual perception
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Perceptually relevant characteristics of light
Humans sensitive to wavelengths between 400 and 700 nanometers
Hue=wavelength (composed of Red, Green, Blue) Brightness=amplitude Saturation=purity of color, undiluted by achromatic
gray or white light
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CIE color space
http://www.linocolor.com/colorman/colorman_frames.htm
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The receptor system: The eyeball
http://www.adobe.com/support/techguides/color/colormodels/cie.html
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Distribution of rods and cones
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Implications of eyeball characteristics
Foveal vision of 2 degrees (cones) surrounded by peripheral vision (rods)
Fovea (cones) sensitive to detail, greater acuity/ Periphery (rods) sensitive to motion
Rods sensitive to light provide night vision, but lose sensitivity when exposed to bright light
Cones sensitive to color Differential sensitivity to red light makes it possible to
engage cones and preserve sensitivity of rods
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8http://www.usd.edu/psyc301/CSFIntro.htm
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Adjustable contrast ratio and spatial frequency
http://webphysics.ph.msstate.edu/jc/library/30-7/
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Basic sensory limits
Contrast ratio (ratio of light to dark) and spatial frequency (level of detail) determine visibility
Color deficiency (red==green) affects 7% of males therefore design for monochrome
Sensitivity of rods to peripheral motion and cones reduced sensitivity to detail in low light “overspeed” at night
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Applications of basic perceptual limits to design
Contrast ratio and text conspicuity (not black on black for warnings as on many VRCs)
Optimal size/level of detail 3 cycles/degree (11 point font)
Use of mixed case in print conveys information through low frequency aspects of word shape
Avoid excessive detail in icons
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Perceptual processing: Bottom up/Top down
Bottom up: Interpretation of stimulus driven by data in the world
Top down: Interpretation of stimulus driven by knowledge in the head
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Bottom-up and Top-down processing
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Perceptual processing: Depth perception
Bottom up• Accommodation: Activation of ciliary muscles• Convergence: “cross-eyedness• Binocular disparity: Different image in each eye
Top down• Linear perspective• Relative size• Interposition• Light and shading• Texture gradients• Relative motion
Design applications:
One-eyed soccer player and 3-D virtual reality
Pavement markings and speed control
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Depth cues at work
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Traffic circle application of depth cues
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Perceptual processing: Visual search
Unstructured visual search time= (N*I)/2• N=number of targets• I=search time per target
Unstructured visual search is not exhaustive
Design applications:
Cost of clutter, eliminate unnecessary items (BU)
Make critical items more salient (color, contrast) (BU)
Structure visual field (alphabetical, consistent location) (TD)
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A visual search challenge
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Perceptual processing: Visual search
Bottom up factors affecting search time:• Conspicuity (color, size, brightness, motion, simplicity,
automaticity) Top down factors affecting search
• Expectancies (knowledge of organization, knowledge of likely location)
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Some Interesting Demos
http://www.usd.edu/psyc301/psyc301main.htm
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Perceptual processing: Detection
Described in terms of signal detection theory (SDT)
SDT defined by two parameters• Sensitivity (d’): Ability to differentiate signal from noise• Response style (Beta): Risky vs. conservative
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Signal detection theory
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Affecting detection bias and sensitivity
Sensitivity (d’): Ability to differentiate signal from noise• Experience• Visual template• Redundant representations• Alertness, frequent breaks• Slow down rate of decisions Response style (Beta): Risky vs. conservative• Value and costs of hits, false alarms (motivation)• Introduce false signals
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Perceptual processing: Discrimination and Absolute judgement
Going beyond detection to categorize or to judge magnitude
3.3 vs. 33 Norflox vs. Norflex (typed and handwritten) Absolute judgement: Attaching labels to levels
• Limited to 5 levels at most• No more than seven colors • Accuracy limited to half the distance between scale
markers
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Absolute judgement in value estimates
Judgement accuracy limited to 1/2 the distance between markers
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Key concepts
The computer as a metaphor for human information processing, and not
Rods,cones, and their capabilities and limits The relationship between contrast sensitivity,
spatial frequency, and visibility Perception depends on relative values than on
absolute values
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More key concepts
Depth perception and the one-eyed soccer player Sensitivity and bias and their effect on detection Discrimination and absolute judgement (limited to
at most 5 levels)
Bottom-up and top-down processes combine to guide visual perception