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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 theoryReview: Norman’s model of actionUser errors and types of errorExamples

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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'?

More info Index Glossary

HelpInformation about whatelephants eat for breakfast,lunch and tea.

More info

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Quizz:

What do you see?

1)

2)3)

4)

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 constructedno prior knowledge involvedactive exploration of environmentConcern:

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 thingprimarily those fundamental properties that determine how

the thing could possibly be usedprovide strong clues to the operation of thingsactual and perceived causalitiesexamples: 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 cycleConcerned 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

The World

Perception

Goal

Intentionformation

Action specification

Execution

Evaluation

Interpretation

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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 visibleGood conceptual model-> consistent system

imageGood mappings that reveal the relationshipsContinuous feedback

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Points Where Errors Occur

User forms inadequate goalsUser fails to find the correct interface object

because of incomprehensible labels or iconsUser does not know how to specify and/or

execute a desired actionUser receives inappropriate or misleading

feedbackDoes 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 whator 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 enginesCrew felt vibration and smelt smokeHealthy 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 engineVibration & 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

FO: shuts right engine down

Failure to review actions

Confirmation bias

Failure to notice display indications

Availability bias

Procedure violation

Faulty mental model

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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 monitorsNo "red zone",

no alert

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Example: Mont Sainte-Odile

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 adjacentetc.

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Designing for error

Many strategies for reducing error problemsMake 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 theoriesEcological theories: affordanceNorman's action cycle to place errorsSlips (unintentional) and mistakes (intentional)Designs can influence the occurrence of errorFeedback 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.