4 Human-Object Interaction
In the previous lecture:
In this lecture:
Why are so many of our artefacts so difficult to use?
...because they have been poorly designed! This is not good enough!
Spherical compass Pocket compass (antique) Gimbled Ship's Compass (antique) Silva orienteering compass
Alessi juicer (by Philippe Starck)
Balls - throwing
Knobs - turning
Handles - grasping
Glass - looking through (or breaking)
Paper (and toilet doors) - writing on
Finger holes in scissors
Push-plates on a door
Shape of an Australian mains power plug
Functions on a digital watch
Operations entered on a command-line UNIX interface
The more possible interpretations a thing has, the more difficult it will
be to use.
Consider the following door mountings. What affordances do they offer? What constraints do they impose?
Mappings (in general) are relationships between things.
In terms of design, mapping might be between controls, their movements, and the result of the operation on/in the world.
Natural mapping leads to immediate understanding because it takes advantage of physical analogies (folk physics) and cultural standards: a close and natural relationship between control and function.
A car steering wheel - the direction the driver turns the wheel top matches the direction the car steers.
A formula-1 car steering wheel. Is this intuitive? (http://www.f1technical.net/article30.html) How does this device make affordances visible to the driver?
An aeroplane joystick - pushing it forward (away from the pilot) drops the nose of the aeroplane (away from the pilot).
The joystick (front/bottom and left of center) is just one of many visible controls. A pilot does not have time to cycle through a series of menus to locate various functions of his control. (http://staff.tay.ac.uk/bstmjc/mjc_research1.htm)
A boat tiller - pushing it to the right (starboard) of the boat, pushes the front (bow) of the boat to the left (port). Why is it designed this way? Does it matter?
Rising level - indicates 'more' of something and vice versa, as does an increase in numeric value and, in Western (English speaking) culture, left to right.
Light switch position - up indicates 'off', down indicates 'on' (in Australia)
What might an increase in pitch (of an audio tone) indicate?
- People will always make mistakes (too err is human )
- Bad design blames the user for incorrect operation (self blame)
- Complex systems still need to be learned
- People's understanding of the world is not, in general, the same as that of experts
- Refusing to believe the evidence instruments indicate that something is wrong is something really wrong or are the instruments wrong?
The action cycle: execution and evaluation
Some design questions
How easily can a user...
...determine the function of the device?
...tell what actions are possible?
...tell if the system is in the desired state?
...determine mapping from intention to physical movement?
...determine mapping from system state to interpretation?
...perform the action?
...tell what state the system is in?
Try to remember the layout of the QWERTY keyboard in these ways:
Which key is above and slightly to the left of the F key? Difficult?
Pretend to type an F on the desk in front of you. Now type an R. Easy?
Types of knowledge:
To help a person perform a task, put as much carefully organised information in the world as possible.
Employ physical and cultural constraints to prevent them from making an invalid action and to assist them in making a valid one.
How does this ticket machine employ the principles we have discussed to assist the user?
Is it well designed? Why or why not?
Knowledge in the world:
Knowledge in the head:
Applications to Multimedia and User-Interface Design
Visibility: make the functions clear. Differentiate opposing functionality. Use visual function to confirm the user's mental model of operation. Sometimes sound can be used to make things visible (e.g. vacuum cleaner clogging up).
Feedback: give actions immediate feedback, to reinforce the user's mental model.
Design for error: people make mistakes for many reasons. Good design accepts mistakes as a normal part of operation and accommodates them.
Try to minimize the causes of errors by understanding them.
Make actions reversible (undo).
Make it easy to discover when errors do occur and make them easy to correct.
Think of "actions as approximations of what is desired", as opposed to "user errors".
Forcing functions: provide constraints of operation in certain situations.
Metaphors: "In theory, an interface designer adopts a metaphor as a means of making the application easier to learn. This theory is based on the premise that the user will be able to transfer his or her knowledge of a familiar object structure to the new application.
In practice however, an interface designer often adopts a metaphor as a means of expressing his or her model of how the system is organized. That the metaphor might make the application easier to use is often an after-the-fact and unsubstantiated rationalization of the design." (Interface Hall of Shame)
In your own time:
Have a look at the two images of graphical user interfaces below. Carefully assess them for their designers' use of the principles covered in this lecture. Choose some software on your own computer and give it the "once over" to see how well its designers considered these same principles.
Apple Quicktime movie player interface
Omni Group Omnigraffle drawing package interface
Some web sites of interest:
An understanding of cognitive design can assist in creating high-quality, user-centered objects, interfaces and multimedia.
Courseware | Lecture notes
©Copyright Alan Dorin 2009