9: Motor Behavior Models

Question 1

Models are used to:

Answer 1

1. used to simplify reality
2. understand, design evaluate system
3. help HCI developers and designers understand workout
   - how interface will perform tasks
   - how efficient is it
4. 2 types
   - predictive
   - descriptive

Question 2

Predictive models

Answer 2

1. allows mathematical prediction of human performance without experiments
2. no need working algorithm
3. metrics of human performance determined analytically without
   - time-consuming, resource-intensive experiments
   - allow design scenario to be explored hypothetically
4. forecast events without research
5. AKA performance models

Question 3

what is Pointing, what devices do we use to point

Answer 3

1. fundamental operation for mouse
2. typing, selecting, dragging, resizing all require pointing
3. pointing devices
   - finger
   - mouse
   - trackpad

Question 4

Fitt’s Law is able to:

Answer 4

1. predict time to point to an object using a device as a function of distance from the target, and target width
2. predict human movement and motion based on time and distance (psychomotor behaviours)
3. models user perform target acquisition

Question 5

Fitt’s Law formula

Answer 5

MT = a+b logbase2(D/W + 1)

measures movement time

Question 6

Index of difficulty formula

Answer 6

ID = logbase2(D/W + 1)

measures difficulty

Question 7

Index of performance formula

Answer 7

IP = ID/ MT

measures performance

Question 8

Fitt’s law calculations show that:

Answer 8

1. movement time increases linearly with ID
   - slower when target is smaller and further
   - moving faster makes it less accurate
2. ID and IP measured in bits
3. IP allows comparison of targeting effectiveness

eg.
device     IP bits/s
hand        10.6
mouse     10.4
touchpad 1.6

Question 9

How do users target

Answer 9

1. rapid ballistic movement towards the target

2. small corrective movements

Question 10

improvements based on Fitt’s Law

Answer 10

1. increase width
2. reduce distance
3. support ballistic and corrective movements
4. edge and corner of screen form infinitely large targets
   - cannot overshoot
   - position important features there
5. use physical constraints
6. group similar interactions

Question 11

what is prime pixel

Answer 11

reference used for where current cursor is

Question 12

What are descriptive models

Answer 12

1. describe framework for thinking about a problem
2. used to inspect ideas or system and make statement about probable characteristics
3. provide basic understanding, reflecting, reasoning
4. reveal flaws in design and style of interaction

Question 13

What is Buxon 3 state model

Answer 13

1. simple expression of the operation of computer pointing devices in terms of state transition
2. how can important properties of device and interactive techniques be characterized in terms of states
3. recognise and explore relationship between pointing device and interaction techniques
4. determine how easy it is to use mouse

Question 14

Buxton example 1: mouse out of range

Answer 14

state 0: out of range
clutching and repositioning mouse on mousepad

state 1: tracking
moving tracker symbol about a display

state 2: dragging
moving an icon on desktop or grouping set of items/range of text

Question 15

Buxton example 2: mouse within range

Answer 15

state 1: tracking
moving mouse cause tracker to move on screen

state 2: dragging
pressing mouse over item permits it to be dragged when mouse is moved
releasing button returns to stage 1

Question 16

Buxton example 3: touch screen

Answer 16

state 0: out of range
movement of finger is not registered

state 1: tracking
finger touches screen and movement starts to get registered.