Change in response to users' actions
Lets users know that they're interacting
Immediate, simple response often useful
Can be visual, auditory, haptic
Delay between an action and its result
Humans very aware of latency > ~ 100 milliseconds
Many delays inherent in different stages of hardware/software
"End-to-end" latency = total delay
Long latency slows up user
Irregular latency even worse
Latency is distinct from update speed
Measure of how many distinct values a device can report
On/off switch = 1 bit resolution
"Non-analog" joystick = 3 values (+1, 0, -1) for X and for Y
8 bit resolution joystick = 256 possible values for X and for Y
16 bit resolution joystick = 65536 possible values for X and for Y
Signal = the information we want to communicate to the computer (e.g. button state, pointer position)
Noise = variations in the signal, outside of our control
Examples:
Applications may need to allow for noise in input data
From human movement research - Paul Fitts, 1954
Predicts time needed to move from a starting position to a target - e.g. to point at something
D = distance to target
W = width of target
