DOET 4

Knowing what to do

Question of the day!

• One way we know what to do is to use knowledge in the world and one type of this is Constraints

• Constraints come in 4 flavors:

– Physical

– Cultural

– Logical

– Semantic

• A phone rings in the room. You answer it.

• The doorbell rings. You go to the front door.

• Which constraint is acting here?

Another question:

• You are hooking up an electronic device. It has 3 connectors and you have 3 cables. One of the cables is red and the other cable is blue. One of the connectors is red and another is blue. You now know where to connect the third cable.

• What kind of a constraint is operating here?

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– At a funeral? Dress in black, Speak in hushed

tones…

• 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 can signify a problem– The lack of a vent-fan sound leads one to

believe that the fan is not working

Rest of the chapter

• The problem with doors– Pull bar or push bar?– Which side has the hinges?

• The problem with switches– They all look alike

• Make them different

• Group them by function

• Tie them to a diagram of a physical space

The End!