3 Introduction to HCI - Human Factor Theories - Mental Models and Problem Solving. Mental models are useful example: the bath tub faucets

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1 Design thinking Human Factor Theories Part I - Mental Model & Problem Solving School of Computer and Communication Sciences EPFL Dr. Pearl Pu What is common in all of these? 2 Mental Models The first question: how to use it Definition: mental models are representations in the mind of real or imaginary situations The mind constructs "small-scale models" of reality that it uses to anticipate events Mental models can be either constructed from the way a system looks, how it behaves, or from a metaphor of a situation already known to us Read further in Sharp et al. 2006, pages Mental models are useful example: the bath tub faucets Mental models allow people to make predictions about how things work and how to use something - How does your car start? - How does an ATM machine work? - How does your computer boot? We use mental models to deal with new and unfamiliar environments based on our existing knowledge A bathtub with two faucets and one spout One faucet for hot water and one for cold water

2 What is wrong here? Psychological variables differ from physical ones Psychological and physical variable Psychological variables User requirements Psychological variables are task oriented parameters with which users manipulate to control the achievement of their tasks (flow, temperature) Physical variables are artifact related parameters with which artifacts function (left faucet for cold water, right faucet for hot water) Users care about rate of total flow and the temperature of water in the tub Total flow = sum of two Temperature = difference or ratio Incorrectly derived mental model Example: a refrigerator w/ freezer Normal Settings Colder Fresh Food Coldest Fresh Food Colder Freezer Warmer Fresh Food OFF (FR & FTRZ) C and 5 C and 6-7 B and 8-9 D and 7-8 C and Set both controls 2 Allow 24 hours to stabilize A B C D E

3 A mental model for refrigerator What is the system image? Freezer Freezer control Freezer Cold Air Fresh food Freezer Fresh food control Cooling Unit Appears that the higher the number, the colder it is for the fresh food unit. The other control unit, A-E is for the freezer, where A is the warmest and E the coldest. Cold Air Cooling Unit Example: a refrigerator w/ freezer Normal Settings Colder Fresh Food Coldest Fresh Food Colder Freezer Warmer Fresh Food OFF (FR & FTRZ) Freezer C and 5 C and 6-7 B and 8-9 D and 7-8 C and coldest coldest 1 Set both controls 2 Allow 24 hours to stabilize Fresh Food Suppose the freezer is too cold, the fresh food section just right. How do you adjust the controls? Answer: keep the numerical setting unchanged. Change the alphabetic setting, C -> B A B C D E The model in reality The model in reality Freezer Control A There is only one thermostat and only one cooling mechanism. One control adjusts the thermostat setting, the other the relative proportion of cold air sent to each of the two compartments of the refrigerator. Freezer Fresh food Valve Cold Air Cooling Unit Control B

4 Freezer is too cold, fresh food section okay. How to adjust the controls? The previous answer ( keep the numerical setting unchanged. Change the alphabetic setting, C -> B) will not be exactly correct anymore. Correct answer: lower control A (C-> B), and lower control B (5->4) to reduce the air going to freezer. Exactly how much, you d have to find out in 24 hours User s and designer s mental models Gulf of execution Designers of (physical) systems construct their mental models of how the system should function. This is called the design model. The user s model: Users develop their own mental models of how their tasks should be accomplished, and through interacting with the system. System image: this is the mental model that users derive from interacting with the (physical) structure. This image is the only way designers communicate to users. Gulf of execution is the distance between user s goals and the methods disposable to achieve them through the system Read further in Sharp et al. 2006, page Read further in Sharp et al. 2006, page Gulf of execution mental model principles Designer s Model User s Model User 1. Many HCI designs fail due to wrong mental models lack of it imprecise or wrong Designer system System Image 23 24

5 mental model principles mental model principles 2. Simple ways to build mental models - mental model analysis; list the main requirements - identify user task variables - ask: do we have all the GUIs for users to accomplish these tasks? 3. If you want users to follow you - Correctly convey the designer s model via the system image Gulf of execution Problem Solving Problem solving How to buy a book from Amazon.fr For a user to interact with a computer or its software, it is a problem solving process. According to the American Heritage Dictionary: - Problem solving is the process of devising and implementing a strategy for finding a solution or for transforming a less desirable condition into a more desirable one. When solving problems, we: - Set up goals - Plan our actions - Execute actions - Evaluate if actions help us achieve goals - Change strategies if necessary Read further in Dix et al. 2004, pages Problem solving cycle Problem solving cycle in more details start here start here Goals Goals Execution Evaluation Execution Intention to act Sequence of actions Evaluation Evaluation of interpretations Interpreting the perception Execution of sequence of actions Perceiving the state of the world The World Read further in Dix et al. 2006, pages The World

6 problem solving principle #1 Visibility 31 problem solving principle #2 32 problem solving principle #3 Arbitrary Informative fdback Clear visual mapping back right front left back left Confirm the result of a process Help users evaluate the effects of their actions. front right 24 possibilities, requires: -visible labels -memory Read further in Sharp et al. 2006, pages Informative fdback continued: Examples: Two types of feedbacks can be identified: articulatory and semantic. Articulatory feedback confirms users haptic skills r.s.p. to the choices as users go through them; Semantic feedback confirms users cognitive skills r.s.p the choices as users go through them. 34 Objects that give articulatory feedback - Surgery simulation tools which provide force feedback; - Isomorphic joysticks and track-points (provides force feedback) - Keyboards

7 Examples: Give specific feedback for what s going on Objects that give semantic feedback - Progress bar - Confirmation messages of user actions -. What s it doing?! > Doit > Doit This will take 5 minutes... Time for coffee Specific feedback continued: Feedback given along several dimensions Provide specific feedback within the context of the action What mode am I in now? What did I select? How is the system interpreting my actions? How quickly a feedback should be given? problem solving principle #4 0.1 second max! perceived as instantaneous 1 second max! user s flow of thought stays uninterrupted, but delay noticed 10 seconds! limit for keeping user s attention focused on the dialog. > 10 seconds! user will want to perform other tasks while waiting. Help users finish her task Task closure - the end of all steps involved in accomplishing a task Nielson, J., Usability Engineering, AP Professional Press, Boston MA,

8 Task closure Designers should allow users to reach the task closure without having to distract their attention by forcing them to work in different windows, traversing a long list of choice items. Designers should help users focus by providing clear cues for context switching if side paths are necessary problem solving principle #5 How do people accomplish complex tasks? Breakdown a complex task - top-down or bottom up - in the top-down approach, a user divides a task into subtasks, then divides subtasks into sub-subtasks. Then he solves a small unit of the problem, and backtracks to upper levels in order to proceed In the bottom up approach: a user constructs solutions to small chunks of problems. Then he constructs a bigger solution by combining small solutions. In reality, people employ a hybrid approach. Example: writing a scientific article Stacking of sub-problems problem solving principle #6 When solving problems in the top-down approach, intermediate solutions need to be memorized (stacking of solutions) so that user can concentrate on solving small tasks at the bottom level. In the bottom-up approach, sufficient methods should be provided to combine small solutions. How do I get out of this?

9 Provide preemptive exits problem solving principle #7 Users don t like to feel trapped by the computer! - Should offer an easy way out of as many situations as possible Strategies: - Cancel button (for dialogs waiting for user input) - Universal Undo (can get back to previous state) - Interrupt (especially for lengthy operations) - Quit (for leaving the program at any time) - Defaults (for restoring a property sheet) When to let users perform multitasking (when attention can be divided) People are accustomed to carry out numerous tasks at the same time. But in a demanding environment like the cockpit, when multitasking is performed, humans need cognitive aids to get reminded of certain crucial moments Routinized tasks Difficult tasks A routine task: a prescribed, detailed course of action to be followed regularly; a standard procedure. Reading, writing, speaking in a native language, riding a bike, typing, putting your foot on the gas pedal, and even skiing. The execution of these tasks eventually becomes automatic. Certain tasks, however, remain difficult, such as spelling your name backward, programming a piece of code, or drawing something meaningful. That s called problem-solving which requires full attention What can be routinized? Humans can do one problem-solving task at any given time, while they may be able to perform several routine tasks simultaneously, or one problem-solving and one routine task simultaneously. The so-called sensory-motor tasks can often be made automatic Cognitive tasks are more difficult to be made automatic. However, it is easier to change a controlled process than a routine process. Try to drive your friend s car (in england), or type the text on an american keyboard

10 When to multitasking? 7 problem solving principles Make most interaction activities as routine as possible Users can concentrate on problem solving Try to be as consistent as possible with assignment of key strokes. Ctrl-P for printing Later Ctrl-P for page layout or next page Once learned, it s difficult to unlearn the routine tasks. 1. visibility 2. clear visual mapping between task and control 3. feedback 4. task closure 5. piece wise problem solving 6. preemptive exists 7. when to multitasking