The bandwidth of a substitute channel is usually far below the original
Aliases: bandwidth · capacity gap · reduced fidelity
What it is
A substitute channel carries far less information than the original. Converting images to tactile dot patterns sharply reduces the detail available per second; converting a complex soundscape to vibration leaves far fewer discriminable categories. Substitution therefore always involves compression.
Why it happens
The bandwidth gap follows from the receiving channel's physical and perceptual limits: touch resolves time and space less finely than vision, and vibration offers fewer discriminable categories than sound—both hard constraints. Compression forces a choice about which features to keep, and the choice follows the task: reading needs the distinguishing features of letter shapes, localization needs directional relations, not every pixel. Designing a substitute is thus less about raising bandwidth than about selecting the most task-relevant features within it.
Studying it
Measure the substitute's actual capacity: estimate the number of discriminable categories through identification tasks, or gauge efficiency at a fixed bandwidth through metrics such as reading speed. Variables include the encoding scheme, task type, and training. Outcomes include category count and task efficiency, which together tell you whether the bandwidth supports the task.
Where it stops holding
When the task needs less information than the substitute provides, bandwidth is not a constraint—distinguishing a few states, for instance. When the task depends on high-resolution detail, a substitute struggles to match the original's efficiency even with training, and the task itself should be redesigned or supplemented. Training improves extraction efficiency but does not widen the channel.
Applying it
- Identify the features the task most depends on and preserve those first within the bandwidth.
- Assess the substitute's discriminable category count and confirm it covers the states the task must separate.
- For tasks exceeding the bandwidth, split them into simpler tasks or add supporting means.
- Verification: measure discriminable category count and task efficiency, confirming capacity meets the requirement.
Related
- Within the group: D5.05.1 Information from one sense can be encoded into another channel · D5.05.3 Substitution demands significant learning
- Adjacent: D2.05.2 Vibration cannot carry as much information as sound · D3.10.1 Most people reliably distinguish only single-digit numbers of haptic patterns
- Search terms:
channel bandwidth·information capacity·feature selection