Usability - cognitive Factors - Baobab Health Trust, March 2014

Baobab Health, March 2014Harry Hochheiser, harryh@pitt.edu
Introduction to Human-Computer
Interaction – Cognitive Issues
Attribution-ShareAlike

CC BY-SA
Harry Hochheiser
University of Pittsburgh
Department of Biomedical Informatics
harryh@pitt.edu
+1 412 648 9300

What is usability?
!
What does it mean to be usable?
!
Which factors influence usability?
!
How can we make an interface usable?
!
Is interface design an art or a science?
!
Goal – develop some intuitions

What does it mean to be “usable”?
!
Find something usable
!
Software, hardware, etc.
!
Why is it usable? What do you mean when you say that?
!
Something unusable?
!
What doesn't work? What's hard?

Usability Successes

Usability Failures

A Usability Failure
The light switch in my office…

A Usability Failure
Control to turn off light sensor

A Usability Failure
Controls??
How might we improve
upon this?

Dimensions of Usability
!
Efficiency
!
Learnability
!
Memorability
!
Error Handling/Prevention
!
Satisfaction

Efficiency
!
Can the system be used to complete the specified task?
!
How much time does it take to complete a task?
!
How many operations?
!
How much movement?

Learnability
!
How quickly can a novice learn to use tool?
!
What help/assistance is given?
!
Consistency with similar system and/or convention?

Memorability
!
Retention of proficiency over time?
!
Reminders and cues
!
Recognition vs. Recall
!
Minimizing cognitive load

Error Prevention/Handling
!
What is the error rate?
!
Slips vs. mistakes
!
Preventing errors
!
Responding to errors

Satisfaction
!
Do users feel that the tool was usable?
!
Do they want to use it more?
!
Is it aesthetically appealing?
!
Don Norman: “Attractive things work better”

Tradeoffs/challenges
!
Efficiency vs. Learnability
!
Expert interfaces
!
Learnability vs. power/expressive control?
!
Power tools may be hard to learn
!
Satisfaction vs. learnability
!
Hidden interactions on tablets
!
Efficiency vs. Errors?

Human Abilities
Motor Abilities: How we can manipulate our world
Perception: What we take in from surroundings
Cognition: What we know
Capabilities influence theories, models, guidelines, etc.
leading to interfaces based on realistic understanding of
what people can do and how they can work.
not how we think they should work.

Motor abilities
• How quickly can we move around?
• Cost of various actions
• mouse vs. keyboard?
• cut down on number of steps required?
Fitts's law: time between two targets is proportional to
distance + inverse of size of targets:
a – start time, b - speed of device, d- distance, w – target widths

BAOBAB JAMA video..
BAOBAB Screen shots.

Perception
Visual
Tactile
Auditory
Taste/Smell
rarely used in HCI

Visual Perception
Good use of Contrast/Color help
except when they don't – color blindness
Which is easiest to read and why?
What is the time?
What is the time?
What is the time?
What is the time?
What is the time?
What is the time?

show baobab web site.

Pre-attentive Processing
• Limited set of visual properties are processed pre-attentivel
without need for focusing attention
• < 200 - 250ms qualifies as pre-attentive
• Important for design:
• what can be perceived immediately: things pop out
• what properties are good discriminators
• Color, shape
• what can mislead viewers
• Combinations may not be pre-attentive

Find the red circle

Not Pre-attentive: conjunction  
of shape and color

• Pattern perception driven by
• proximity
• similarity
• smooth/good continuation
Perceptual Grouping - Gestalt

Grouping
Rosenholtz, et al. 2009

Cognitive concerns
Attention
Memory
long-term
short-term
Language: reading, speaking, listening
Problem solving: planning, reasoning & decision-making
Learning

Attention
We don't see -or “attend to” most of the world around us
attention -filtering out the noise
without attention, we'd couldn't function
how do we capture attention
“retinal attributes” intensity, marking, size, fonts, color..
change
• movement
• lights
• sound
• etc..
Cost of capturing attention: distraction

Question: When to claim attention?
Want to notify users of problems
Each claim on attention has a cost
context-shift takes time, loses focus
When should an interface interrupt the user?

Change Blindness 
http://www.youtube.com/watch?v=Ahg6qcgoay4

Short-term Memory
temporary recall
small - 7 +/-2 “chunks”
• George Miller – remembering strings of numbers
rapid access, rapid decay
repeat to send to long-term
sometimes used in interaction design.
not necessarily appropriate.
• interfaces are about recognition
• STM is about recall

Long-term memory
Huge capacity
Slow access, decay
episodic: events and experiences
semantic: structured records of facts, concepts, skills.

Examples of ways that interfaces
can work with memory constraints?
• Don't overtax short-term
• excel copying
• Help build long-term
• consistency
• (don’t force people to remember what’s been entered -)
• vb screenshot.

Conceptual models
!
Mental constructions that describe how something works
! or how you think it works
Good models help with predictability
key concept in HCI
To build good conceptual model
must understand the way users work and approach problems
otherwise, you get interfaces that reflect models from the designer,
organization, etc., that don't reflect how users work.
Deep vs. shallow
deep – understanding of mechanisms - “white box”
shallow – how to use something - “black box”

Whose conceptual model?
Don Norman, Design of Everyday Things

Norman's Refrigerator Thermostat
Don Norman, Design of Everyday Things

Norman's refrigerator thermostat 
Mental Models
It's been > 15 years since I first read this book, and I'm
still confused by this model.
.. and my fridge is still not correctly adjusted.

Examples of mental model  
mismatches?

Language: reading, speaking, listening
• We're good at these things
• but, they require attention
• May distract from other tasks
• don't like to read manuals
• try listening to the news while you work on computer
• Speech recognition: thinking about your voice controls may
interfere with language tasks (i.e, writing)

Problem solving: planning, reasoning &
decision-making
• When solving the problem of how to accomplish a task with
the computer..
• System should help figure out next tasks
• logical design – visibility and mapping
• When trying to use the computer to solve a problem
• System should get out of the way
• Not distract from focus on problem
• interfaces that disappear
• No one wants to just “use the computer” - they want to accomplish
goals

The Psychopathology of Everyday Things 
Don Norman – Design of Everyday Things, Ch. 1
Favorite quote: “if a door handle needs a sign, then its
design is probably faulty”
“When simple things need pictures, labels, or instructions, the design
has failed”
Thinking about how design relates to human psychology
ideally, design should be consistent with how we think
Learn from failures
Principles all applicable to computer interfaces

Norman's Seven Stages of Actions
Form goal
Form intention
Specify action
execute action
perceive state
interpret state
evaluate outcome
Cycles
evaluation – mismatch between system output and user expectations

Gulfs of Execution and Evaluation
User Goals System
Capabilities
Gulf of Execution - interface design
Intentions Action
Specification
Interface
Mechanism
Gulf of Evaluation - information design
Interface
Display
InterpretationEvaluation

• Goal: Enter a new prescription
• Initial intention: How do I decide where to start?
• selecting a medication…
• Action Specification: Once I know first step, what do I
do?
• Interface Mechanism: which buttons do I press, in
which order?
Gulf of Execution

• After execution
• Interface display: What happened/changed in response to
my action?
• Interpretation: What does it mean?
• Evaluation
• did the right thing happen?
• am I closer to my larger goal?
• do I need to change my goal or my choice of tactics?
Gulf of Evaluation

Bridging Gulfs
Execution
clarity of action
Transparent interfaces with affordances
Wizards
Help/Tutorials
Evaluation
Feedback
Explanation
Error Messages
Undo

Affordances
“actionable properties between
the world and an actor (a person or animal).”
(Gibson, quoted by Nielsen http://www.jnd.org/dn.mss/affordances_and.html)
“Perceived affordance” - design that communicates
possibility of an action to the user.
What makes an affordance? Examples?

Models
Response time - how long it takes from initiation to display of results
Think time – time before starting next action
As response time decreases, approach simpler model
Interface can help reduce planning time?
How to measure think time?

• Predictive Models of task completion times
• Motion
• Button press
• Think, etc.
• CogTool: www.cogtool.com
Keystroke-Level Models &
Goals, Operators, Methods,
Selection Rules

Cogtool and ANC

Cognitive Load, Errors, and
Response Time
More effort spent planning and waiting increases cognitive
load and short-term memory - more errors
But, errors are more expensive
vicious cycle
Interruptions can be expensive
derail thinking/flow

Mappings
Correspondence between
what you want to do
what appears to be possible
You want to go forwards/backwards, but controls are only up and
down
visibility indicates mapping between intended actions and
operations.
Light switches in order of where the lights are?
Good mappings reduce cognitive overload
leverage previous knowledge

Mapping Successes and/or Failures?
Refrigerator controls -
2 controls implies 2 systems to regulate
Others?

Visibility
• “correct parts must be visible, and they must convey the
correct message”.
• “natural signals”
• What's natural in a computer interface?
• what's intuitive?
• What does visibility look like?
• Is strict visibility crucial?
• Weaker notion: parts that aren't immediately visible should be findable
in appropriate places?
• “Whenever the number of possible actions exceeds the number of
controls, there is apt to be difficulty.”

• Interfaces are languages
Levels of Visibility
Lexical-Syntactic-Semantic-Conceptual
Foley & van Dam, as interpreted by Myers
(http://www.cs.cmu.edu/~bam/uicourse/830spring13/830-09-softorg.pptx)
Letters/Words Sentences Paragraphs Ideas
Lexical Syntactic Semantic Conceptual
Keys, Buttons, Sequences Tasks Domain Concepts

• Spelling and composition of “tokens”
• “add” vs. “append” vs “^a” vs
• Location of controls
• “Key-stroke”
• Make items visible
• Distinguish between items that can and cannot be acted
upon
Lexical Visibility
Myers http://www.cs.cmu.edu/~bam/uicourse/830spring13/830-09-softorg.pptx

• Ordering of inputs
• Legal a tokens must sensible order in?
Syntactic Visibility
• Tokens must be used in a legal, sensible order.
• Visual cues can improve visibility
• Gray out inactive/inappropriate items
• Grouping and spacing

• System functionality
• High-level tasks
• Patient creation
• Patient lookup
• data retrieval
• How do sequences of actions complete a task?
• Task sequence and completion indicators
• Wizards
• Titles/screen layout
Semantic Visibility

• Conceptual (definition from Foley & Van Dam text, 1st edition)
• key application concepts that must be understood by user
• User model
• Objects and classes of objects
• Relationships
• Operations
• Example: text editor
• objects = characters, files, paragraphs
• relationships = files contain paragraphs contain chars
• operations = insert, delete, etc.
Conceptual Visibility
Myers http://www.cs.cmu.edu/~bam/uicourse/830spring13/830-09-softorg.pptx

Feedback
Action without impact is potentially problematic.
as is reducing complex set of actions to one piece of
information (done/failed)
or, lack of feedback on long-running actions
Don't know if your action has taken place or not
so, you do it again
Therac 25

Errors, Mistakes, Slips
Slips – you know what to do, but you do the wrong thing
Mistake – incorrect mental model
Examples ? Slips? Mistakes?

How to tell the difference?
!
Mistakes are based on difficulty in underlying mental
model
!
But, mental models aren't visible
!
Must elicit model from user
!
“think-aloud” protocols –User describes actions, goals,
ideas, as they do the work.
!
Statements that suggest a mental model might be
inconsistent with system model → mistakes

System
Capabilities
Execution, Evaluation, Mistakes, Slips
User Goals
Gulf of Execution - interface design
Intentions Action
Specification
Interface
Mechanism
Gulf of Evaluation - information design
Interface
Display
InterpretationEvaluation
SlipsMistakes
Slips
Mistakes

How to redesign to avoid slips?

How to redesign to avoid slips?
Clarity in labeling?
Clear affordances
Mapping
Visibility
Feedback..
Undo!

Redesign to avoid mistakes?

Redesign to avoid mistakes?
Preferred approaches:
Revise the system model to meet the user model
Revise work and information flow.
Acceptable:
Increase visibility, feedback, mappings of the system
model
Not mutually exclusive!

Slips and Mistakes in Clinical Informatics
Why so important?
Factors that distinguish clinical informatics from other
settings?
“To Err is Human” 1999 – Institute of Medicine

A cognitive taxonomy of medical errors 
Zhang, et al. 2004
System Hierarchy

U = f(u,c,t,s)

U → usability

u → user

c → context

t → task

s → system

A cognitive taxonomy of medical errors 
Zhang, et al. 2004

Usability - cognitive Factors - Baobab Health Trust, March 2014

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Usability - cognitive Factors - Baobab Health Trust, March 2014