ergonomics –the study of work. origins in wwii as more controls and devices were added to british...
TRANSCRIPT
Ergonomics –The Study of Work
Origins in WWII As more controls
and devices were added to British combat planes
pilots made more errors,
endangering the missions
Affordances
Ergonomics studies the range of normal Human Abilities and
Limitations
Mappings & Affordances
• Mapping is the relationship between objects. Turn the steering wheel right the car goes right.
• Turn signals on a motorcycle: flip up, flip down – bad UI
Novice Users
– Confused– Willing to learn– Makes errors of understanding– Blames themselves
Intermediate Users
– Confident– Makes slips, not erros– Invokes “magical thinking”• Herbert Simon – Satisficing
Folk theories – eg: Turning the thermostat on high will heat the house faster– Timer theory – thermostat controls how long the device is on– Valve theory: like a hose – turn up the valve and increase the
rate of heat flow
The theory may be incorrect but it should be usable
Expert Users
– Confident– Explains and understands why things work– Able to use tools in innovative ways– Tends to blame the designer
Types of Errors
• Capture Error - where one frequent behaviour replaces another (drive to work instead of a friend’s)
• Descriptive Error – use the wrong object which has a similar use – throw spaghetti into the garbage instead of a pot
• Data Driven errors– Metathesis in typing– Entering an old phone # instead of new one– Slips of the tongue
Types of Errors Continue• Associative Activation Errors
– Pick up phone and saying come in– Answering office reply at home
• Loss of Activation Error– Start on one activity (going to the next room) and forgetting
why you went• Mode errors
– When different devices have different modes of operation and you use the wrong command
• Target errors – When you go for one control instead of the other
(maybe the ejection button shouldn’t be next to the ignition)
The Human Eye has Rods and Cones
Rods detect black and white and allow us to discern lines and edges – they are shape detectors
Cones allow us to detect colour
Distribution and Sensitivity of Cones
Visual Acuity of the Human Eye
• ½’ of arc to distinguish pixels• 18’ of arc to distinguish text(Assuming vision corrected to 20/20)
Always check the distance from the monitor and compare to monitor specs.
1’ (one minute) of arc = 1/60th of a degree
Visual Acuity
A Too Small To Read
This is large enough to read
18’ of arc
½’ of arc
Too close – one can see individual pixels
Good! Pixels blend together
Eye Hand Co-ordination
Fitt’s Law for Reaction Time
T = k0 + k1 log2(Distance/Size +.5)
There is a minimum reaction time.The Further the hand has to travel the longer it takes. The Smaller the object the Longer it takes.
Big objects close by are quickly and accurately clicked. Small objects far away take longer and are easily missed