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DOET 4. Knowing what to do. Knowing what to do. A design signals how it is to be used Natural physical constraints Affordances suggest possibilities Constraints limit the possibilities The chess example:
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DOET 4 Knowing what to do
Knowing what to do • A design signals how it is to be used • Natural physical constraints • Affordances suggest possibilities • Constraints limit the possibilities • The chess example: • Experts can reconstruct a chess board after being given 10 seconds to memorize it, novices can’t • BUT: Only if the chess board contains chess pieces in legally attained locations.
Constraints, four flavors • Physical • Can’t physically do it wrong • Semantic • Rely on our knowledge of the situation and the world • There is a bear in the cave • The bear in the cave is a brown bear • Cultural • Signs are meant to be read • Logical • Only one piece left, only one place you can put it
Physical constraints • Rely on properties of the physical world for their operation • No learning required
Semantic constraints • Rely on the meaning of the situation • There is only one meaningful way for a rider to sit on a motorcycle • There is only one meaningful place for the windshield; in front of the rider • Learning is required; semantic constraints rely on our knowledge of the situation and the world
Cultural constraints • Signs are meant to be read and therefore must be right side up • Red is culturally interpreted to mean stop; green, to go. • Behavior in social situations is culturally defined; restaurant behavior applies to all restaurants
Cultural constraint How are they represented in the mind?) • Schemas are used to represent these cultural constraints • Schemas… • Contain the rules and information necessary to interpret the situation • Schemas may include scripts • Scripts guide the sequence of behavior
Logical constraints • If you have a choice of two possibilities and cultural or semantic constraints dictate where one goes, then a logical constraint dictates the other • Natural mappings provide logical constraints (left switch, left light…)
A single design guideline • Make controls that do different things look and feel different • Nuclear power plant beer tap (yikes!) • Backhoe example: running a backhoe you stay pretty busy and don’t have the time to look to make sure you grab the right lever • Lift bucket (longer) • Rotate bucket (shorter)
Sound increases visibility?!? • Auditory feedback can tell us about the state of the system without having to look at it. • Sound can provide feedback about events • The absence of expected sound signifies a problem • The lack of a vent-fan sound leads one to believe that the fan is not working
incomplete... • complete from • “The problem with doors” p87