In the context of 2D Fitts’s Law for pointing, what do the ‘Distance’ (D) and ‘Width’ (W) variables represent?
‘Distance’ (D) is from the current cursor position to the center of the target. ‘Width’ (W) is the width of the target measured along the direction of movement.
According to the principles discussed, what are the fastest points to access on a display screen from any location?
The corners and edges of the display are the fastest to access.
How does the formula for the Index of Difficulty (ID) differ between a standard pointing task and a steering task?
For a pointing task, the ID is log^2(D\W). for steering through a tunnel the ID is D\W
In the Keystroke-Level Model (KLM), what do the operators ‘H’, ‘M’, and ‘P’ represent?
H: ‘Homing’ (moving the hand between mouse and keyboard), M: Mental acts, and P: Pointing with a mouse to a target.
What are the advantages of using the Keystroke-Level Model (KLM) for analysis?
Its advantages include simplicity, applicability from just sketches, surprising accuracy for routine tasks, and its utility in comparing design alternatives.
Fitts’ Farm Study
A study comparing finger to stylus input for a drag-and-drop task on a tablet, conducted with 8 and 9-year-old children.
Key Concepts in Human Movement (Fitts’ Law)
Includes the Speed-Accuracy Trade-off, Index of Difficulty (ID), building a Fitts’ Law Model, and the Throughput of Input Devices.
Types of Input Models Discussed
Includes the application of Fitts’ Law, Pointing and Crossing models, the Steering Law, and the Keystroke-Level Model (KLM).
2D Fitts’s Law
An extension of Fitts’s Law that models movement time (MT) when a user is moving in two dimensions (x and y).
Goal-Crossing Model
An interaction style, emerging from the pen/stylus era, where selection is made by crossing through an object without needing to stop within its boundary.
Pointing vs. Crossing Interaction
In Pointing, control and correction happen at the end of the movement when stopping on an object. In Crossing, control and correction occur throughout the movement while passing through an object.
Goal-Crossing Model Formula
The formula to calculate movement time (MT) for trajectory-based task, expressed as MT = a+b*log^2(d\w +1)
Keystroke-Level Model (KLM)
A model that defines a set of basic input operators (physical motor, mental, and system response) with time estimates to predict the time for a user to complete a task.
Operators in the Keystroke-Level Model (KLM)
Basic actions with time estimates, including K (Keystroke), P (Pointing with a mouse), H (‘Homing’ hand between devices), and M (Mental acts).
Throughput (in HCI)
A measure of input performance that takes into account both the speed and accuracy of an input device.
Assumptions of Fitts’s Law
The model presumes that the target’s location is known in advance (eliminating search time) and that the target can be reached in a single, uninterrupted movement.
‘K’ Operator (Keystroke) in KLM
Represents pressing a single key. The associated time varies by user skill: 0.12s for an expert (90 wpm), 0.28s for an average non-skilled user (40 wpm), and 1.2s for someone unfamiliar with the keyboard.
“Tunnels” in a User Interface
A concept related to the Steering Law where a user’s movement is continuously constrained, such as when navigating through a hierarchical submenu.
‘R(t)’ Operator in the Keystroke-Level Model (KLM)
Represents the system response time, which is the duration during which the user must wait for the system and cannot perform any other actions.
In the Fitts’ Farm study, what was a qualitative observation made about the dragging paths when children used their fingers?
The paths were described as ‘childish’ looking.
According to the provided examples, what is the effect on Movement Time (MT) when a 1D target is changed to a 2D target, effectively increasing its width along the axis of approach?
MT decreases because the effective target width (W) increases.
The Goal-Crossing model, which became prominent in the Pen/Stylus era, was specifically instigated by studies on what type of interaction?
“no-click” interaction
In the Keystroke-Level Model (KLM), what does the operator ‘D(nD, lD)’ represent?
Drawing nD straight line segments of a total length lD.
What is the specific time estimate for the ‘H’ or ‘Homing’ operator in the Keystroke-Level Model (KLM), representing the movement of a hand between mouse and keyboard?
0.4s
