Consistency and Inconsistency in Interaction
Using computers involves a large number of actions on the part of the user which is often performed at a very rapid rate. Actions such as pointing, clicking, dragging, placing have to be done in repeated cycles by the user. This often leads to forming a habit for a given interface environment. If the dialog between the user and the interface consists of random patterns it leads to increase in cognitive load. It is therefore important for interactions to be not only reliable but also consistent across all interfaces constituting a task. Inconsistency leads to unpredictability contributing to inefficiency. Errors could creep in. In this experiment you will experience the need for being alert, attentive and quick in reacting to stimuli from a computer screen. Though the experimental situation and interaction situation is simple the chances of committing errors are still there. On screen where large amount of data need to be interacted with (E.g.: an account sheet containing thousands of individual numbers) making the interface interactions consistent becomes important.
Theo Mandel in his book titled “The Elements of User Interface Design John Wiley & Sons” has written about the principles of consistency as follows :
Principles that make the interface consistent
1. Sustain the context of users’ tasks (continuity)
2. Maintain consistency within and across products (experience)
3. Keep interaction results the same (expectations)
4. Provide aesthetic appeal and integrity (attitude)
Consistency in presentation
Consistency in presentation means that users should see information and objects in the same logical, visual, or physical way throughout the product. If static text information is in blue on one screen, then static text on all other screens should also be presented in blue. If a certain type of information is entered using one type of control, then use that same control to capture the same information throughout the product. Don’t change presentation styles within your product for no apparent reason.
Consistency in behaviour
Consistency in behavior means that the way an object works is the same everywhere. The behavior of interface controls such as buttons, lists, and menu items should not change within or between programs. I’ve seen programs where the menu bar choices immediately performed actions, instead of displaying pull-down menus, as everyone expects. Users should not be surprised by object behaviors in the interface.
Consistency in interaction techniques
Interaction technique consistency is also important. The same shortcut keys should work in similar programs. Mouse techniques should produce the same results anywhere in the interface. Keyboard mnemonics should not change for the same menus from program to program. Users expect the same results when they interact the same way with different objects.
( Source : The Elements of User Interface Design , By Theo Mandel , John Wiley & Sons )
Ben Shneiderman an American computer scientist at the Human-Computer Interaction Laboratory at the University of Maryland has come up with eight golden rules in which Consistency has also been mentioned. The eight golden rules have been reproduced below.
Shneidermans "Eight Golden Rules of Interface Design"
1. Strive for consistency : Consistent sequences of actions should be required in similar situations; identical terminology should be used in prompts, menus, and help screens; and consistent commands should be employed throughout.
2. Enable frequent users to use shortcuts : As the frequency of use increases, so do the users desires to reduce the number of interactions and to increase the pace of interaction. Abbreviations, function keys, hidden commands, and macro facilities are very helpful to an expert user.
3. Offer informative feedback : For every operator action, there should be some system feedback. For frequent and minor actions, the response can be modest, while for infrequent and major actions, the response should be more substantial.
4. Design dialog to yield closure : Sequences of actions should be organized into groups with a beginning, middle, and end. The informative feedback at the completion of a group of actions gives the operators the satisfaction of accomplishment, a sense of relief, the signal to drop contingency plans and options from their minds, and an indication that the way is clear to prepare for the next group of actions.
5. Offer simple error handling : As much as possible, design the system so the user cannot make a serious error. If an error is made, the system should be able to detect the error and offer simple, comprehensible mechanisms for handling the error.
6. Permit easy reversal of actions : This feature relieves anxiety, since the user knows that errors can be undone; it thus encourages exploration of unfamiliar options. The units of reversibility may be a single action, a data entry, or a complete group of actions.
7. Support internal locus of control : Experienced operators strongly desire the sense that they are in charge of the system and that the system responds to their actions. Design the system to make users the initiators of actions rather than the responders.
8. Reduce short-term memory load : The limitation of human information processing in short-term memory requires that displays be kept simple, multiple page displays be consolidated, window-motion frequency be reduced, and sufficient training time be allotted for codes, mnemonics, and sequences of actions.
(Source : Designing the User Interface by Ben Shneiderman, Fifth Edition , Pearson Education India )
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