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ITCS 6010
Laws Of Interface Design
1. User Control
The interface will allow the user to perceive that they are in control and will allow appropriate control.
1. User Control
There is a difference between feeling in control and actually being in control.
Our goal is the user should feel in control.
1. User Control
User who feel in control can: Predict what the computer will do next Take the next action they decide is
appropriate at their choice Go back and fix problems Work the way they want to, not changing their
work to accommodate the computer’s interface
1. User Control
VUI users can feel the lost of control quickly because the computer is speaking and may take control of the conversation
Solutions Barge-in, allow the user to interrupt the agent Error recovery for speech errors
2. Human Limitation
The interface will not overload the user’s cognitive, visual, auditory, tactile or motor limits.
2. Human Limitations
Memory People can remember 5 – 9 things for about
20 seconds in their short term memory, unless the information is chunked, i.e. phone numbers (704) 687-7988.
Adding semantic meaning “The Magical Number Seven, Plus or Minus Two” (Miller, 1956)
eibjwlfikqqk dogcatcowpig
2. Human Limitations
Decision Making People give early evidence too much significance. If
they receive 1 piece of information early, they believe it over what they hear later.
People do not extract as much information out of the data they have.
People are more sure of their decision as they get more information, even if the quality of the information is bad.
2. Human Limitations
Decision Making People seek more information than they can
actually handle or extract data from. People can only deal with 3 or 4 hypotheses at a
time. People focus only on a few attributes. People seek information that confirms a decision
they have already made. Engineering psychology and human performance (Wickens, 1984)
2. Human Limitations
Visual People do not read everything on a screen, page
or window. People will not find information on a full or
cluttered screen. People are easily distracted by visual stimuli such
as graphics, animations or too much information. People have trouble reading fonts that are too
small or vary in style too much.
2. Human Limitations
Motor People can not hit targets that are too small on
the screen. People may have trouble double-clicking. People do not always realize they can or should
drag and drop. People do not like constantly switching between a
mouse and keyboard. People need time to adapt to new input devices.
2. Human Limitations
Speech People have more trouble remembering
messages spoken in synthetic speech versus natural speech, unless trained to do so.
Use slow speech to increase user encoding of messages (this is for novice users).
3. Modal Integrity
The interface will fit individual tasks within whatever modality is being used: auditory, visual, or motor/kinesthetic.
3. Modal Integrity
Some tasks are best performed using speech, others using vision or others with motor/kinesthetic or tactile modes.
Some are best performed using multiple modes.
3. Modal Integrity
Auditory modality is best when Information is short and simple Information is needed immediately, but not later
(doesn’t have to be remembered) Information is temporal in nature (refers to events
over time) The message is a critical warning A verbal response is required
3. Modal Integrity
Auditory modality is best when The visual system of the person is already
overextended The environment is not conducive to a visual
display (i.e. driving a car) The person needs to stay “dark adapted” The person needs to be moving continually
3. Modal Integrity
Visual modality is best when Information is complex and long Information needs to be remembered The information deals with spatial relationships,
i.e. maps The person’s audition is overextended The environment is noisy
3. Modal Integrity
Visual modality contradictions Information is complex and long
People summarize information when it is large Information needs to be remembered
Seven plus or minus 2 The information deals with spatial relationships,
i.e. maps People deal with verbal navigation well
3. Modal Integrity
The average time it takes a person to hear a signal and make a simple response is 150 milliseconds.
The average time it takes a person to see a signal and make a simple response is 200 milliseconds.
Robert Bailey, Human performance engineering. 1982.
4. Accommodation
The interface will fit the way each user group works and thinks.
4. Accommodation
The system should adapt or accommodate itself to the user, not the other way around.
This is accomplished using a User Centered-Design approach.
5. Linguistic Clarity
The interface will communicate as efficiently as possible.
5. Linguistic Clarity
Refers to the clarity of the language of the application, not the clarity of the monitor.
An interface has linguistic clarity when it provides context and speaks in the user’s terminology.
5. Linguistic Clarity
Context The language is related to the nature or context of
the application. Example:Equipment Instructions:
First, sort the items into like categories. Sorting by color is common, but you can also use the other characteristics, such as texture or type of handling needed. Once you have sorted the items, you are ready to use the equipment. You want to process each category from the sorting separately.
5. Linguistic Clarity
Context The language is related to the nature or context of
the application. Example:Using Your New Washing Machine:
First, sort the items into like categories. Sorting by color is common, but you can also use the other characteristics, such as texture or type of handling needed. Once you have sorted the items, you are ready to use the equipment. You want to process each category from the sorting separately.
5. Linguistic Clarity
Context Spoken words can lose context quickly versus
words that appear as labels on a screen.
Terminology The language uses terms that are familiar to the
user.
6. Aesthetic Integrity
The interface will have an attractive and appropriate design.
6. Aesthetic Integrity
Refers to the issue of preference. It is not possible to separate human performance
from preference.
A study showed that users preferred a voice that was casual and used the first person, I, compared to others (Susan Boyce 1999).
6. Aesthetic Integrity
Normally, people prefer natural voices, but synthetic voice are more appropriate for warnings and alerts (Cohen & Oviatt 1994).
Alert, Alert …
How may I help you?
7. Predictability ***
The interface will behave in a manner such that users can accurately predict what will happen next.
7. Predictability
Users Mental Model = Conceptual Model This makes the interface predictable.
Predictability is crucial to speech interfaces. If your interfaces is not predictable, then the help
or instructions must be exceptional, which is difficult because of human memory. There is only so much you can say before they user forgets what was said.
8. Interpretation ***
The interface will make reasonable guesses about what the user is trying to do.
8. Interpretation
The system should be able to monitor user behavior and make a reasonable guess as to the action or speech the user is trying to apply Speech recognition plays a huge role in
interpretation. Misinterpretations are a problem. Context aware systems can help enhance
interpretation.
9. Accuracy
The interface will be free from errors.
9. Accuracy
Complete accuracy is impossible.
The goal is to significantly reduce errors. Error reduction techniques will be discussed later.
10. Technical Clarity
The interface will have the highest possible fidelity.
10. Technical Clarity
Refers to the level of quality or fidelity of the interface. Visual interfaces with technical clarity have high
resolution and easy to view graphics. Kinesthetic interfaces have buttons that are easy
to discern and easy to press. Speech interfaces will have sounds and speech
of high quality.
11. Flexibility
The interface will allow the user to adjust the design for custom use.
11. Flexibility
Allows users to customize the interface for their own work. Differs from accommodation, which adjusts the
interface to match the way users work.
Accommodation accounts for what 80% of the users need to do 80% of the time.
Flexibility accounts for the other 20%.
11. Flexibility
Speech examples of flexibility. Barge-in Ability to exit to an operator Users can customize menus
12. Fulfillment
The interface will provide a satisfying user experience.
12. Fulfillment
User has a satisfying experience with the interface. We will discuss how to measure this using the
PARADISE Framework later.
Fulfillment techniques Offer a better way to do something Performs basic tasks effectively Match current work process
13. Cultural Propriety
The interface will match the user’s social customs and expectations.
13. Cultural Propriety
User now expect that their computers will interact with them the way humans do. People treat machines like people (Reeves & Nass, The
Media Equation, 1995)
Users may understand they are speaking with a computer and not a person, but that does not mean that they expect any less. This does mean that they may become more
tolerant of errors.
13. Cultural Propriety
Cultural Propriety can be accomplished using User Centered Design.
14. Suitable Tempo
The interface will operate at a tempo suitable to the user.
14. Suitable Tempo
Important due to temporal nature of speech Pace too slow => frustrated user Pace too fast => confused user
User Centered Design will accomplish a suitable tempo.
15. Consistency
The interface will be consistent.
15. Consistency
If the interface is inconsistent, this limits predictability.
Example “Go Forward” is an acceptable command,
therefore, it is consistent to use “Go Back” or “Go Backwards”.
“Last” or “Previous” would be inconsistent.
16. Forgiveness ***
The interface will make actions recoverable.
16. Forgiveness
We must assume that errors will occur, and therefore build mechanisms into the interface to handle the errors in as forgiving a way as possible. We will discuss error handling and forgiveness in
more detail later.
17. Responsiveness ***
The interface will inform users about the results of their actions and the interface’s status.
17. Responsiveness
Users need feedback on their actions and feedback on the system’s actions. Feedback is especially important in VUI.
Responsiveness in speech When should the user speak? Who’s turn is it to speak?
Responsiveness is related to User Control.
Laws Of Interface Design These laws serve as a guideline to interface development
in general.
We will discuss more specific VUI design guides next.
