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User Interface/Interaction Design
One Aspect of Product Design


Prof. David Bernstein
James Madison University

Computer Science Department
bernstdh@jmu.edu

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What is User Interface Design?
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  • Recall:
    • Software product design is the process of specifying software product features, capabilities and interfaces to satisfy client needs and desires. (Fox, 2006)
  • One Implication:
    • Interface design is part of product design
What is a User Interface?
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  • Defined:
    • A system that allows for interaction between a human and a device
  • Input:
    • Keyboard (structured, natural language)
    • Speech Recognition (structured, natural language)
    • Pointing Devices
    • Optical Gesture Recognition
  • Output:
    • Display (textual, graphical)
    • Printer (textual, graphical)
    • Speech Generation (structured, natural language)
    • Haptic Devices
Some of the Physics, Biology and Psychology Behind User Interface Design
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  • The Senses and Sensors
    • Sight (i.e., the eye)
    • Sound (i.e., the ear)
    • Touch
    • Smell and Taste
  • The Model Human Processor
    • A simplified model human sensing, storage, and perception
Sight
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  • The Eye:
    • images/eye.gif
  • The Process within the Eye:
    • Light waves (transverse electromagnetic waves) enter through the cornea
    • Are focused by the lens
    • Stimulate sensors in the retina
Sight (cont.)
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  • Rods:
    • Output impacts our perception of luminance/brightness
  • Cones:
    • \(\beta\) sensors are sensitive to wavelengths between 400 and 550 nm, but are most sensitive to a wavelength of 450 nm (what we call blue)
    • \(\gamma\) sensors are sensitive to wavelengths between 420 and 660 nm, but are most sensitive to a wavelength of 540 nm (what we call green)
    • \(\rho\) sensors are sensitive to wavelengths between 400 and 700 nm, but are most sensitive to a wavelength of 580 nm (what we call red)
  • Lens:
    • Highly separated wavelengths can't be focused simultaneously
    • Yellows with age (and, hence, filters out blue wavelengths)
Hearing
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  • The Ear:
    • images/ear.gif
  • The Process within the Ear:
    • Sound waves (longitudinal mechanical waves) are collected by the auricle
    • Pressure changes cause the eardrum to vibrate
    • Vibrations are amplified by the ossicles
    • Vibrations are transferred to endolymph fluid in the cochlea
    • The basilir membrane vibrates at a particular location
    • The stereocilia stimulate sensory cells
    • The resulting electrical impulses are transmitted by the auditory nerve
Hearing (cont.)
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  • Volume:
    • Difference in amplitude (measured in decibels)
    • Audible Sounds: 0dB
    • Painful Sounds: 120dB
  • Pitch:
    • Differences in frequency (measured in Hz)
    • Acoustic Signals: 15Hz to 18kHz
  • Timbre:
    • Pronounced tam-bur
    • Includes the waveform's distribution of energy at different frequencies (i.e., spectra) and its envelopes/transients (i.e., the attack, sustain and decay)
The Model Human Processor (Card, Moran and Newell; 1983)
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  • Motivation:
    • Interaction involves the user providing input to the computer in response to a change in the user interface
    • This involves sensing, processing/perception and physical movement
  • A Difficulty:
    • These are very complicated processes
  • Our Approach:
    • Use a low-resolution model
The Model Human Processor (cont.)
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  • Perceptual Processor:
    • Takes inputs from the eyes and ears
    • Makes changes to the visual image store and auditory image store in working memory
    • Processing times of 50-200 millis
  • Motor Processor:
    • Controls muscles
    • Processing times of 25-170 millis
  • Cognitive Processor:
    • Operates on data from working memory and long-term memory
    • Makes changes to working memory
    • Processing times of 30-100 millis
The Model Human Processor (cont.)
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  • Working Memory:
    • Capacity of 5-9 (\(7 \pm 2\)) "chunks"
    • Decays in 5-226 sec
    • Rehearsal slows decay; interference hastens decay
  • Visual Image Store:
    • A frame is represented/encoded as a description
    • Each frame is 7-17 "chunks"
    • Each frame decays in 70-1000 millis
  • Auditory Image Store:
    • A sound is represented/encoded as samples
    • Each sound is 4.4-6.2 "chunks"
    • Each sound decays in 900-3500 millis
Fitts's Law
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  • Putting It All Together:
    • The time to acquire a target (\(T\)) is a function of the distance to (\(D\)) and size of (\(S\)) the target
    • \(T = a + b \cdot \log(D/S + 0.5)\)
  • Implications for GUIs:
    • Location matters
    • Size matters
Analysis for User Interface Design
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  • Analysis for Product Design:
    • Other Aspects - Lists of needs and desires focus on functionality (i.e., "what")
    • UI Design - Focuses on the form of the interaction (i.e., "how")
  • Understanding the Form:
    • Characterizing users based on how they will use the system
    • Understanding the workflow (i.e., how various functions will be combined)
Analysis for User Interface Design (cont.)
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  • Characterize/Categorize Users Based On:
    • Education/training
    • Familiarity/expertise with input devices
    • Age
    • Sex/Gender
    • Language
    • Domain/application expertise
  • Identify Workflows:
    • The order in which the tasks (from the list of needs and desires) will be performed
  • Keep in Mind:
    • 80% of users use a small number of features; 20% of users use a large number of features
Resolution for User Interface Design
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  • Parts of the Process:
    • Define interface objects
    • Define events that will cause changes to the state of the UI
    • Depict each state of the UI
    • Indicate how the user should interpret the depiction
  • Iterations:
    • Early depictions/prototypes are often low fidelity (e.g., storyboards on paper)
    • Later depictions/prototypes are often simulations with a human in the loop
    • "Final" depictions/prototypes eliminate the human
Resolution for User Interface Design (cont.)
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  • Formative Evaluation of Early Protoypes:
    • Use guidelines/heuristics (e.g., from Nielsen, Tognazzini, Norman, etc...)
  • Formative Evaluation of Later Protoypes:
    • User testing
Guidelines related to Cognitive Processing
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  • Simplicity/Clarity:
    • Break long/complex sequences/tasks into shorter/simpler sequences/tasks
    • Avoid ambiguity
  • Consistency/Stability ("Principle of Least Astonishment"):
    • Use consistent terminology, icons, colors, etc... within the product
  • Familiarity:
    • Be consistent with expectations from other products
    • Be consistent with the real world (e.g., use appropriate metaphors)
Guidelines related to Cognitive Processing (cont.)
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  • Discoverability:
    • Allow users to discover functionality
  • Availability:
    • "Important" features should be readily available
    • Provide alternative ways to access features/accomplish tasks
  • Responsiveness:
    • Provide articulatory feedback (i.e., about physical actions) and semantic feedback (i.e., about intentions) as quickly as possible
    • Use user-centered (rather than product-centered) messages (e.g., don't include messages like "Error 101")
  • Forgiveness:
    • Allow users to fix mistakes
Guidelines Related to Perception
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  • Text:
    • Don't user more than 3 fonts
    • Don't use more than 4 different font sizes
    • Use sans-serif fonts for headings/titles; use serif fonts for text (though sans-serif fonts are a little easier to read on displays)
    • Use case appropriately
    • Use underlining sparingly
    • Use italics and bold consistently
    • Use concise, unambiguous language
  • Color:
    • Don't use red or green in the periphery of the visual field
    • Don't use red/green, blue/yellow, green/blue, and/or red/blue combinations
Guidelines Related to Perception (cont.)
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  • Layout:
    • Don't change much from "screen to screen" within a task
    • Keep related items near each other and unrelated items far from each other (i.e., group by proximity)
    • Provide an initial point of focus
    • Use a balanced layout (i.e., distribute elements equally around an axis or axes)
    • Labels can be aligned on the left OR right; Widgets/controls should be aligned on the left AND right
  • Dynamics:
    • Use animation to clarify consequences
    • Use animation to slow processing to a human time frame
  • Contrast:
    • Use contrast (in color, texture, shape, position, orientation, size) to display salient differences in easily perceptible and appropriate ways
Guidelines Related to Perception (cont.)
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Nerd Humor
http://imgs.xkcd.com/comics/only_serifs.png
(Courtesy of xkcd)
Formative User Testing
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  • Participants:
    • User - Thinks aloud while performing tasks
    • Facilitator - Provides the tasks and encourages discourse
    • Observer - Watch for and record critical incidents
  • Study Design:
    • In practice, a single user will find 12%-60% of usability problems
    • So (for each category of user) 5 users will find most (typically 85%) problems
There's Always More to Learn
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