Traditional Interface Design

Principles:

1 - Recognize Diversity
    diversity of users
        novice / first time users
            novice - no little task or interface concepts
            first time users - have task conceps but shallow knowlege of interface
            need to be able to accomplish basic needs with small number of consistent actions
        knowledgeable intermittent users
            know about the task and general knowledge about the interface - will forget specific features
            need to easily rediscover how to perform tasks
        expert frequent users
            thoroughly familiar with task and interface concepts
            need ability to quickly carry out actions, get rapid reponses, brief feedback
    diversity of tasks
        determine set of tasks early in design
        choose 'atomic' actions
        look at task frequencies
    diversity of interaction styles

 

	Advantages	Disadvantages
Direct Manipulation	-visually presents task concepts  -allows easy learning  -allows easy retention  -allows errors to be avoided  -encourages exploration  -affords high subjective satisfaction	-may be hard to program  -may require graphics display and pointing device
Menu Selection	- shortens learning  - reduces keystrokes  - structures decision making  - permits use of dialogue management tools  - allows easy support of error handling	presents danger of many menus  may slow frequent users  consumes screen space  requires rapid display rate
Form Fillin	- simplifies data entry  - requires modest training  - gives convenient assistance  - permits use of form management tools	- consumes screen space
Command Language	- is flexible  - appeals to 'power' users  - supports user intiative  - allows convenient creation of user-defined macros	- has poor error handling  - requires substantial training and memorization
Natural Language	- relieves burden of learning syntax	-requires clarification dialogue  - may require more keystrokes  - may not show context  - is unpredictable

 
2- Eight golden rules of interface design

    a strive for consistency
    b enable frequent users to use shortcuts
    c other informative feedback
    d design dialogues to yield closure
    e offer error prevention and simple error handling
    f permit easy reversal of actions
    g support internal locus of control
        - make users the initiators of actions, want users to feel they are in control
    h reduce short term memory load
        - 7 +/- 2

3-Prevent Errors

Based on previous user studies there are certain principles within the field

model human processor

chunks

    BCSBMICRA
 

    CBSIBMRCA

    reading:
        250 words per minute
        familiar words recognized by shape

        9-12 font size equally legible given proportional spacing between lines
        line lengths between 2/3 and 5.2 inches equally legible
        positive contrast (light on dark) are preferred and show better performance
        lower case words are read faster than words in upper case
        individual letters and nonsense words UA1416 are read faster in upper case
 

Fitt's Law

    time Tpos to move the hand to a target of size S which lies distance D away is
        T_pos = I_M log₂ (D/S + 0.5) where I_M = 100 [70-120]msec/bit

    Time to move depends on relative position required
    Different constants for different devices
 

Power Law of Practice

    time T_n to perform a task on the nth trial follows a power law
        T_n = T₁n^-a where a = 0.4 [0.2 - 0.6]
 
Keystroke Level Model

        only gives predictions for execution time, not acquisition time (planning)

        K - Keystroking - striking keys
                (pressing a shift or a control counts as a K as well)
                best typist 0.08 sec (135 wpm)
                good typist 0.12 sec (90 wpm)
                poor typist 0.28 sec  (40 wpm)
                non-typist  1.20 sec
        B - Pressing a mouse button
               down or up  0.10 sec
                click            0.20 sec
        P - Moving the mouse at a target
                fitts law 0.1 log2(D/S) + 0.5
                avarage (mouse) 1.10 sec
        H - Homing - switching hand between mouse and keyboard 0.40 sec
        D - Drawing lines using the mouse -
        M - Mentally preparing for a physical action 1.35 sec
        R - System response -

        Ms are hard to place - there are a set of heuristsics (p 267 Card book)

        Say we are using a word processor and see an incorrect character on the screen. We use the mouse  to position the insertion bar, delete the incorrect character, add the new character and then return to where  we were in the document:
 
 

1 - move hand to mouse	H[mouse]
2 - position mouse after bad character	PB[left]
3 - return to keyboard	H[keyboard]
4 - delete character	MK[delete]
5 - type correction	K[char]
6 - reposition insertion point	H[mouse]MPB[left]

 
or we could compare an editing task in emacs and vi and Xemacs
    replace a 5 letter word with another 5 letter word where the replacement takes place one line below
    the previous modification

misc
 

 How useful are all these numbers ...