CMT 3210 Week 8

1. CMT 3210 Week 8 Making Sense of the World: Perception and Human Error Elke Duncker

2. 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

3. 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 Visual Perception

4. 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.

5. 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?

6. Visual Structures • ...and how would you interpret each of the buttons that is labelled 'more info'?

7. Quizz: • What do you see? 1) 4) 2) 3) 5)

8. 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)

9. 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

10. 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

11. 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

12. Identifies components of action Gulfs of execution evaluation Emphasises feedback Allows different kinds of error to be distinguished Norman's Model of Action Goal Intention formation Evaluation Action specification Interpretation Execution Perception The World

13. 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

14. 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? Feedback: Example

15. Norman’s Design Principles • Action alternatives should be visible • Good conceptual model-> consistent system image • Good mappings that reveal the relationships • Continuous feedback

16. 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?

17. 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?

18. 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”!

19. 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

20. 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.

21. 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 FO: shuts right engine down Failure to review actions Example: Kegworth Air Disaster Availability bias Failure to notice display indications Faulty mental model Confirmation bias Procedure violation

22. What happened? • Note the lack of feedback • about state of the aircraft systems • about possible causes • about effects of action • Biases • availability • confirmation

24. Vibration monitors No "red zone", no alert

26. 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”

27. 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.

28. 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

29. 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

30. 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.