Transcript COM 3210 : Understanding the human element in HCI

CMT 3210 Week 8
Making Sense of the World:
Perception and Human Error
Elke Duncker
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Topics
Theories of perception:
review constructivist approach
New theory: ecological approach
Visual structures and principles of Gestalt theory
Review: Norman’s model of action
User errors and types of error
Examples
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Visual Perception
 Review: Constructivist
approaches
Seeing is an active
process
Process of perception
includes interpretation
World is constructed in
one’s mind
 New: Ecological
approaches
process of perception
involves exploring the
environment and picking
up information from the
environment
no construction
no elaboration
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Constructivist Approaches
Our image of the world is not perfect replica of
the world (such as a camera would produce).
Our visual system constructs a model of the
world.
This model influences the perception of
information by transforming, enhancing,
distorting and ignoring it.
The perceived information confirms, changes
and expands the model.
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Visual Perception
Gestalt psychology: we make sense of 'the
whole' and interpret information in context.
E.g. is this a collection of curves or a tree?
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Visual Structures
...and how would you interpret each of the
buttons that is labelled 'more info'?
Information about what
elephants eat for breakfast,
lunch and tea.
More info
Index
Help
More info
Glossary
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Quizz:
What do you see?
1)
4)
2)
3)
5)
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Organising Principles
Proximity: Objects appear as groups not as
random cluster of elements (1)
Similarity: Elements of the same shape or
colour are seen as belonging together (2)
Closure: Missing parts of a figure are filled in
such that is appears whole (3)
Continuity: identical objects in rows are seen
as lines (4)
Symmetry: regions bounded by symmetrical
borders are perceived as coherent figures (5)
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Ecological Approach
Information is detected not constructed
no prior knowledge involved
active exploration of environment
Concern:
which information needs to be picked up
how can it be provided
central concept: affordance
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Affordance
Perceived and actual properties of a thing
primarily those fundamental properties that
determine how the thing could possibly be used
provide strong clues to the operation of things
actual and perceived causalities
examples: door handles (Preece, page 81)
a protruding vertical door handle for pulling
a flat horizontal bar for pushing
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Perception in Interaction
Design
Review: Norman's action cycle
Concerned with
The process how people interpret information from
the screen (of which perception is one step)
Leads to
feedback
errors
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Norman's Model of Action
 Identifies components
of action
 Gulfs of
execution
evaluation
 Emphasises feedback
 Allows different kinds
of error to be
distinguished
Goal
Intention
formation
Evaluation
Action
specification
Interpretation
Execution
Perception
The World
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Feedback
Feedback helps people to form understanding of
the device (cf. mental models)
Also necessary to support user keeping track of
state of device
imagine using a computer with monitor turned off
Important for
Deciding what to do next
Detecting and recovering from errors
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Feedback: Example
 A calculator:
“Clear” key first clears
number then clears
operation?
25 + 15 CE CE —> 25.
Users typically press clear
key many times.
Users typically prefer to
use bits of paper than to
use calculator memory.
Why?
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Norman’s Design Principles
Action alternatives should be visible
Good conceptual model-> consistent system
image
Good mappings that reveal the relationships
Continuous feedback
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Points Where Errors Occur
User forms inadequate goals
User fails to find the correct interface object
because of incomprehensible labels or icons
User does not know how to specify and/or
execute a desired action
User receives inappropriate or misleading
feedback
Does the above remind you of anything?
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Errors
Error types:
Slips: action is not correct for the gaol
e.g. caused by layout (buttons too close together)
'strong habit intrusions'
'mode errors'
Mistakes (or misconceptions): action is correct, but
intention is faulty
e.g., misconception about what does what
or about the state of the system
Other types of errors: e.g. is a post-completion error
a slip?
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Example: "A £10m Glitch in
the System"
“A young trainee working on a simulation of the
markets had inadvertently slipped into the real
world”
£11.5 billion in bonds accidentally sold; cost to
bank: £10m
Real life and "training mode"
Only the word “simulation” in very small letters at the
bottom of the screen indicates which system is in use
"operating a playstation", "supposed to be
foolproof", “impossible”!
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Example: Kegworth Air
Disaster
Failure in one of two engines
Crew felt vibration and smelt smoke
Healthy engine throttled back
Did that cure problem? NO
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Example: Kegworth Air
Disaster
Displayed information would have allowed
problem to be correctly diagnosed.
Displays considered unreliable.
Inference made on (faulty) beliefs about air
conditioning.
Many distractions: radio talk, programming flight
management system.
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Example: Kegworth Air
Disaster
Failure in engine
Vibration & smoke observed
FO: It’s a fire coming through
C: Which one is it?
FO: It’s the le…it’s the right one
C: Okay throttle it back
FO: throttles back right engine
Problem appears to be
cured
Availability bias
Failure to notice display
indications
Faulty mental model
Failure to review
actions
Confirmation bias
FO: shuts right engine down
Procedure violation
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What happened?
Note the lack of feedback
about state of the aircraft systems
about possible causes
about effects of action
Biases
availability
confirmation
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Vibration monitors
No "red zone",
no alert
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Example: Mont SainteOdile
The aeroplane crashed into the Mountain
because descent was too fast
One interpretation of the available data
the pilot entered data to request a descent angle of
3.3 degrees at a time when the flight management
system was accepting data on descent in thousands
of feet per minute
“mode error”
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Example: “Help” Key on
Macintosh
The “help” key is right next to the “delete” key on
the Mac keyboard. I regularly press “help” then
“delete”…
"Caps lock" right next to "a". So I often end up
with MISTAKE LIKE THIS
"Open" and "Close" menu items are adjacent
etc.
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Designing for error
Many strategies for reducing error problems
Make errors detectable
feedback on effects of action; evaluation of goal
Reduce potential for slips
E.g., simplify and indicate modes
Reduce potential for mistakes
E.g., make system state visible
Reduce consequences of error
E.g., make actions undo-able
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Summary
Constructivist theories
Ecological theories: affordance
Norman's action cycle to place errors
Slips (unintentional) and mistakes (intentional)
Designs can influence the occurrence of error
Feedback is crucial
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Further reading
Preece, J. et al. (1994) Human Computer Interaction.
Dix et al. (1998) Human Computer Interaction.
Reason, J. (1990) Human Error.
Norman, D. (1988) The psychology of everyday things.
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