Vibrotactile sensitivity peaks in a specific frequency band

What it is

Detection thresholds for skin vibration are not uniform across frequencies: plotting threshold against frequency produces a U-shaped curve — a middle band requires the smallest amplitude (most sensitive), and the further a frequency sits from that band on either side, the larger the amplitude needed for detection. For glabrous skin (fingertip), this most sensitive band sits around 200–250 Hz.

This entry covers the frequency-to-receptor correspondence — which band is most sensitive — not the integrated percept of texture judgement; using the same vibration information to judge "rough versus smooth" belongs to a separate layer of perceptual integration.

Why it happens

The U-shape comes from different frequency bands being dominated by different receptor channels: the low band (below roughly 40 Hz) is mainly served by slowly adapting afferents (Merkel) and some fast-adapting afferents, which are tuned to static pressure and slow change and respond weakly to high-frequency vibration, needing larger amplitude to trigger sufficient firing. The mid-to-high band (roughly 40–500 Hz) is dominated by Pacinian corpuscles, whose lamellar capsule acts like a band-pass filter most sensitive to a specific frequency range, with the peak landing near 200–250 Hz. Beyond the Pacinian corpuscle's response range (higher frequencies still), transduction efficiency drops and threshold rises again. In other words, the trough of the U-curve essentially marks the frequency range where "the Pacinian channel's response efficiency is highest," not some abstract "skin as an ear" analogy.

Studying it

This curve comes from psychophysical amplitude-detection threshold measurement: a fixed vibrating probe contacts the skin, and at several discrete frequencies a staircase or method-of-constant-stimuli procedure finds the minimum amplitude a participant can detect; connecting the thresholds across frequencies produces the sensitivity curve (classic work includes Verrillo's equal-sensation contour studies). Such measurements are sensitive to contact area, applied force, and skin site, all of which must be checked when interpreting specific numbers.

Where it stops holding

The peak-frequency location shifts with contact area, applied pressure, and measurement site — a larger contact area may shift the peak slightly, and moving the measurement site from fingertip to palm or forearm keeps the curve's overall shape similar but changes both the absolute threshold and the peak location. Individuals also differ in peak frequency, so a value from a single study should not be treated as a fixed constant applicable to everyone.

Applying it

• Most consumer vibration motors (ERM, LRA) have a natural resonant frequency in the 150–250 Hz range, and that's not a coincidence — this band sits right near the peak of human skin's vibration-sensitivity curve, so a relatively small drive energy produces a strong subjective vibration — a natural meeting point of engineering cost and perceptual effect.
• When the goal is the strongest felt sensation for minimum power draw, tune the drive frequency toward the target site's sensitivity peak rather than simply raising voltage/amplitude; for the same energy expenditure, a frequency inside the sensitive band is perceived as noticeably stronger.
• How to check: measure the actual threshold-versus-frequency curve for the target actuator and target site (even just a few key frequency points) to confirm the chosen drive frequency really falls within that site's sensitive range, rather than reusing the classic fingertip curve without verification.

Related

• Same group: A4.03.2 Frequency and amplitude jointly determine perceived intensity · A4.03.3 Detection outside the sensitive band requires more energy
• Nearby: A4.01 Types of cutaneous mechanoreceptors (the Pacinian corpuscle's transduction mechanism) · A4.13 Texture and material perception
• Search terms: vibrotactile threshold · Pacinian channel · frequency sensitivity curve · Verrillo