SIMS 213: User Interface Design & Development Marti Hearst Thurs, Feb 10, 2005

Today Affordances Mappings Mental Models (time permitting)

Cognitive Considerations From Don Norman’s book, The Psychology (Design) of Everyday Things –Affordances, Constraints, and Mappings –Mental Models –Action Cycle and Gulf of Execution

Affordances The perceived properties of an object that suggest how it can be used. Popularized by D. Norman in POET –The perceptual psychologist J. Gibson had a similar, but different, notion. –Norman contrasts real vs. perceived affordances –Subsequent clarifications on affordances by Norman:

Affordances The perceived properties of an object that determine how it can be used. –Knobs are for turning. –Buttons are for pushing. Some affordances are obvious, some learned –Glass can be seen through. –Glass breaks easily. Sometimes visual plus physical feedback –Floppy disk example Rectangular – can’t insert sideways Tabs on the disk prevent the drive from letting it be fully inserted backwards

Norman’s Affordances Affordances: –Have perceived properties that may or may not exist –Have suggestions or clues about to how to use these properties –Can be dependent on the Experience Knowledge Culture of the actor –Can make an action easy or difficult From McGrenere & Ho, Proc of Graphics Interfaces, 2000

Affordances of a Teapot?

Slide adapted from Saul Greenberg

Real vs. Perceived Affordances From design.html : design.html In product design, where one deals with real, physical objects, there can be both real and perceived affordances, and the two need not be the same.

Based on slide by Saul Greenberg Affordances in Screen-Based Interfaces In graphical, screen-based interfaces, all that the designer has available is control over perceived affordances –Display screen, pointing device, selection buttons, keyboard –These afford touching, pointing, looking, clicking on every pixel of the display.

Based on slide by Saul Greenberg Affordances in Screen-Based Interfaces Most of this affordance is not used –Example: if the display is not touch-sensitive, even though the screen affords touching, touching has no effect. –Example: does a graphical object on the screen afford clicking? yes, but the real question is does the user perceive this affordance; does the user recognize that clicking on the icon is a meaningful, useful action?

Visual affordances of a scrollbar

Affordances More examples? See Strauss Mouse Video

Mappings Mapping: –Relationships between two things Between controls and their results –Related to metaphor discussion –Related to affordances

Slide adapted from Saul Greenberg

Mapping controls to physical outcomes back right front left back left front right 24 possibilities, requires: -visible labels -memory arbitrary full mapping back front back 2 possibilities per side =4 total possibilities paired

Mappings For devices, appliances –Natural mappings use constraints and correspondences in the physical world Controls on a stove Controls on a car –Radio volume »Knob goes left to right to control volume »Should also go in and out for front to rear speakers For computer UI design –Mapping between controls and their actions on the computer Controls on a digital watch Controls on a word processor program

Based on slide by Saul Greenberg Transfer Effects People transfer their expectations from familiar objects to similar new ones –positive transfer: previous experience applies to new situation –negative transfer: previous experience conflicts with new situation

Based on slide by Saul Greenberg Cultural Associations Groups of people learn idioms –red = danger, green = go But these differ in different places –Light switches America: down is off Britain: down is on –Faucets America: counter-clockwise is on Britain: counter-clockwise is off

Based on slide by Saul Greenberg Mental Models People have mental models of how things work: –how does your car start? –how does an ATM machine work? –how does your computer boot? Allows people to make predictions about how things will work

Based on slide by Saul Greenberg Mental Models Mental models built from –affordances –constraints –mappings –positive transfer –cultural associations/standards –instructions –interactions Mental models are often wrong!

Slide adapted from Saul Greenberg Our mental models of how bicycles work can “simulate” this to know it won’t work

People are always trying to make sense of things Mental models often extracted from fragmentary evidence People find ways to explain things –Computer terminal breaks when accessing the library catalog –Certain you’re driving on the correct road