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Mouse Pointing (Engelbart, 1968)

Measured by MacKenzie, Sellen & Buxton · ACM CHI 1991 (1991)

Manual Pointing 1968

Inputs

The measured or assumed values behind the calculations, each with its source.

TP = 4.5 bits/s
Fitts' law throughput (index of performance) for the mouse in the 1991 pointing task. Independent reviews (Soukoreff & MacKenzie 2004) place mouse throughput in the 3.7–4.9 bits/s range. The system date is the 1968 Engelbart/SRI public interactive-computing demonstration.

Strictest ITR

Each scoring method is an upper bound on the channel, so the headline is the strictest (smallest) one for this entry. Use the score selector on the home page to view any single method across entries.

Strictest Fitts' law Author-reported · reproduced
Fitts' law throughput, re-derived from the task conditions
2D pointing channel
4.5 bits/s

  1. Information per movement (index of difficulty)

    ID = log2(A/W + 1);  4 amplitudes (8–64) × 4 widths (1–8) fully crossed → ID = 1.0–6.0 bits (mean 3.26 bits/movement)

    Each pointing movement selects among the distinguishable endpoints set by the distance-to-width ratio; that ratio, in bits, is the Shannon information the movement carries. This is the real information calculation; the ×60 below is only a unit change. Task design: MacKenzie, Sellen & Buxton 1991.

  2. Accuracy folded in via effective width

    W → We for the observed 3.5% error rate (Welford normalization, 4% nominal)

    The effective-width correction discounts movements whose endpoints scattered wider than the target, the pointing analogue of subtracting wrong selections, so the bits are net of the user's real hit precision.

  3. Throughput = information ÷ movement time

    mean MT = 674 ms → IP = 4.5 bits/s (Fitts regression over the ID conditions)

What counts as a bit depends on the action space. The number of distinguishable actions and how likely each one is are design choices of the task, not the sensing hardware. The same modality can present a fixed set of targets, a set pruned per step by a grammar or language model, or a continuous control space. Each of these changes how many actions are live and how the probability mass is spread, and therefore the information per selection. Read the action space below before comparing headline numbers across entries.

Action space

What the user can produce at each step, and how those options are distributed.

Structure
Continuous control space
Size
Continuous
Prior
Uniform: all actions assumed equally likely
Notes
A 2D pointing channel; Fitts' throughput already folds in speed and spatial accuracy (it uses the effective target width). A continuous control device, so not directly comparable to discrete spellers, but directly comparable to the cursor BCIs, which report the same kind of bits/s.

Comparability The strictest bound here is Fitts throughput: the index of difficulty, log₂(A/W + 1), per movement. Directly comparable to the other continuous-pointing entries (mouse, trackball, stylus, gaze and the cursor BCIs). Set against the text entries (keyboards, spellers, speech) it crosses methods: both report bits/s, but one measures movement difficulty and the other text information, so compare within the family first.

Source

Authors
MacKenzie, Sellen & Buxton
Publication
ACM CHI 1991, 1991
Paper
10.1145/108844.108868
Reference
System date: SRI history of the 1968 public mouse demonstration
Reference
Soukoreff & MacKenzie 2004: throughput review (3.7–4.9 bits/s for the mouse)