Haptics are poor at conveying quantity and location

What it is

Haptics are poor at expressing quantity and position. Vibration count to mean "three messages" requires counting; placement to mean "chapter two" requires localization, and both push touch onto its weakest dimensions. Touch conveys that a state changed, not by how much or where.

Why it happens

Counting requires holding a running total through a serial, easily interrupted sequence; once attention drifts, the tally is gone. Position coding depends on spatial resolution, which is limited around a single vibration point, and users cannot re-inspect it the way they re-inspect a screen. Both tasks demand deliberate attention, while the value of haptic confirmation is precisely that it needs none—so using touch for quantity or position cancels its advantage.

Studying it

Counting and localization tasks locate the limits: present varying numbers of pulses or different locations (left/right, different zones) and have users report count or position, tracking accuracy as quantity rises. Variables include pulse interval, number of simultaneous channels, and coupling. Record deviation patterns beyond the ceiling, such as systematic under- or over-reporting.

Where it stops holding

Very small quantities—two or three—can be counted when the rhythm is clear, so the boundary widens at low counts. Position coding improves on multi-actuator devices such as a wrist band of motors, though still far below vision. When quantity also appears in text or graphics, users read it directly rather than counting, and touch only needs to signal presence.

Applying it

• Let haptics carry "something changed" and put "how much changed" on the screen or in speech.
• When a few states must be distinguished, use different patterns rather than different pulse counts, so users need not count.
• If a multi-actuator device is used for position, measure its spatial resolution first and stay within it.
• Verification: have users report pulse count or vibration location and tabulate accuracy against quantity; if accuracy falls at low counts, switch to pattern or visual encoding.

Related

• Within the group: D3.05.1 Haptics can confirm an action without looking at the screen · D3.05.2 Haptic confirmation suits binary information
• Adjacent: D3.10.1 Most people reliably distinguish only single-digit numbers of haptic patterns · D4.08.2 In low-load settings, redundancy has limited marginal value and may overload
• Search terms: haptic counting · spatial haptics · quantity encoding