Tongue Drive System (Huo & Ghovanloo, 2008)
Measured by Yousefi, Huo & Ghovanloo · IEEE EMBC (2010)
Inputs
The measured or assumed values behind the calculations, each with its source.
- TP = 1.67 bits/s
- Fitts' law throughput averaged over 6 able-bodied subjects, tracking a magnetic tracer on the tongue. Reported in the 2010 follow-up, which also measured 3.99 bits/s for a mouse and 2.17 bits/s for a keypad under identical conditions. The system date comes from the 2008 Tongue Drive first-demonstration paper.
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.
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Information per movement (effective index of difficulty)
IDe = log2(De/We + 1); 3 distances (80–320 px) × 3 widths (40–160 px) × 8 directions → IDe = 1.58–3.17 bits/movement
Shannon-formulation Fitts task (Yousefi, Huo & Ghovanloo 2010): each tongue-steered cursor movement selects among the endpoints set by the distance-to-effective-width ratio; that ratio, in bits, is the information per movement.
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Accuracy folded in via effective width
We = 4.133 × SDx (SDx = scatter of endpoints along the task axis)
Effective width is computed from where the cursor actually landed, so throughput is net of the user's spatial error, with no separate error term needed.
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Throughput = information ÷ movement time
TP = IDe/MT = 1.67 ± 0.37 bits/s for the tongue (same task, same subjects: mouse 3.99, keypad 2.17 bits/s)
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 tongue-operated pointing channel: a small magnet on the tongue is tracked by external sensors and mapped to cursor motion. Fitts' throughput already folds in speed and spatial accuracy (effective target width), so it is directly comparable to the mouse, trackball, stylus and cursor-BCI entries, which report the same kind of bits/s; the tongue lands at ~42% of mouse throughput.
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
- Yousefi, Huo & Ghovanloo
- Publication
- IEEE EMBC, 2010