Vibration cannot carry as much information as sound

What it is

Tactile channel capacity is low: a vibration motor can reliably convey far fewer discrete states, and far fewer simultaneous events, than sound. What transfers from audio to touch is "something happened" and "which class of thing," not the full information payload the sound carried.

Why it happens

The ceiling comes from two places. Hardware: phone motors express roughly a handful of intensity levels and a small set of rhythms, and their spin-up and spin-down times set a minimum discriminable gap between pulses. Perception: skin resolves space and rapid temporal change less finely than the cochlea, and a vibration must persist long enough to be felt at all, which caps how much can be encoded per unit time. Sound superimposes many frequency components at once; touch struggles to run in parallel, so concurrent events tend to queue serially or drop.

Studying it

Identification experiments with candidate intensity-and-rhythm patterns let you estimate the discriminable set: build the confusion matrix and find the size at which accuracy collapses. Under concurrency, measure the miss rate—how many of two simultaneous haptic events a user can identify. Report the device model, because discriminable range varies greatly across motors and cross-device generalization is unsafe.

Where it stops holding

Training widens the range slightly but does not remove the channel's bandwidth ceiling. Discrimination is best when the device is worn against the body (pocket, wrist) and degrades on a table or under thick clothing. So "vibration can carry equivalent information" may hold locally, for particular devices and wear states, but cannot be a general design premise.

Applying it

• Let touch encode only high-priority, low-information events such as confirmation, warning, and source identity—not text or lists.
• Keep at most one haptic message active at a time; queue or drop the rest by priority and cover the gap visually.
• Treat the haptic pattern table as a finite resource and govern its total size instead of adding patterns case by case.
• Verification: have users identify every pattern in realistic wear states (pocket, hand, table), log confusions and misses, and redesign any set that exceeds the discriminable count.

Related

• Within the group: D2.05.1 Critical information must move to another channel when sound is muted · D2.05.3 Degradation paths must be predefined
• Adjacent: D2.05 Degradation under silence and vibration · D3.10 Discriminable size of the haptic vocabulary
• Search terms: haptic channel capacity · information bandwidth · tactile discrimination