Chapter 4 Flashcards
PoHCI, week 8 (12 cards)
What is motor control?
Refers to the regulation of all movement in a human, including integrating relevant internal and external sensory information to determine the necessary signals to trigger muscles to activate
What is the end-effector?
The body part that we use for something, like pressing a button has the finger has the end-effector
What are the three central motor tasks?
Target acquisition
Simple reaction
Choice reaction
What is target acquisition?
Can either be;
Spatially constrained aimed movements
- Discrete aimed movements are movements to spatially bounded targets
(Example: Clicking a button) - Continuous aimed movements requires keeping a control point without a bounding box
(Example: Following a path or selecting text)
Temporally constrained aimed movements
- Interception task:
Catch a moving object by
1) placing a selector on its future path and
2) pressing the button when the object is within the selector’s effective region (Example: Aiming at
an object and then shooting)
What is pointing and what type of movement is performed?
When you use a pointing device to select or interact with targets (can be with the mouse, finger, stylus
etc.)
Discrete, spatially constrained aimed movement
Explain Fitts’ law
Definition: A mathematical model that predicts that the average movement time required to hit a target
along a one-dimensional path is proportional to the “difficulty” of hitting a target. This difficulty involves
the distance to the target and the width of the target
Predicts movement time (MT) to a known target
Dependent on target distance (D) and target width (W)
Predicts how easy it is to hit a target or how long it takes to hit a target with a pointing device depending on the distance to the target and the width of the target
What did Fitts discover in his experiment?
Movement time increases with distance
Movement time decreases when target area is larger
Doubling the distance has the same effect as halving the target size
What is simple reactions?
Something appears on the display and the user must respond to it as quickly as possible
Among the fastest human responses in HCI
Explain the Ratcliff model
Evidence accumulation model
Perceptual evidence for/against responding to the event on the screen is accumulated until some
threshold is met, and the motor response is launched
Stimulus onset: The event one should respond to appears
After some time the decision process begins and lasts a short while
When the decision process stops, a proper response has been settled and we react accordingly after
a short while
What is choice reaction?
When there are n options available, our performance can be measured as choice reaction time (CRT)
CRT: The time that has elapsed from presentation of the cue to the response
Explain the Hick-Hyman law
Describes the relationship between n and CRT
When the number of response options increases, choice reaction time increases
What is a crossing and a steering task?
Crossing task:
In a crossing task the user does not need to stop within the target, but does need to
ensure the target is crossed
Steering task:
A task where the user is moving a cursor through a form of tunnel constraint
