Your Body Does Not Feel Vibration Evenly. A 2025 Study Shows Why.
A 2025 study mapped how people distinguish vibration across the forearm, abdomen, thigh and lower back. It found that direction, spacing and body location all influence what people can resolve.
Most haptic products are described with numbers: motor count, wattage, frequency range and intensity.
But the body does not experience vibration as a specification sheet.
Where vibration arrives matters. The direction it appears to move matters. The distance between two vibration points matters. And according to a 2025 study published in Scientific Reports, those relationships change across the body.
That caught my attention because SoundBlanket began with a design question: how do you turn music into something the body can feel without reducing the experience to “more bass” or “more power”?
The study does not answer that entire question. It does something more fundamental. It maps how accurately people can distinguish vibration across five measurement sites in four body regions—and shows that our tactile sense is not uniform.
What did the researchers test?
A research team led by the University of Wuppertal recruited 33 adults between 18 and 38 years old.
They tested the forearm, abdomen, thigh and two areas of the lower back: one near the spine and another farther toward the side of the body.
At each location, two small contact points delivered short vibration bursts at roughly 130 Hz. One vibration was followed by another, and participants reported the direction in which the second point moved.
The spacing changed from trial to trial. This allowed the researchers to estimate how much separation people needed before they could reliably recognize the vibration’s direction.
This ability is called vibrotactile spatial acuity: how accurately the body can distinguish where vibration is occurring and how separate vibration points relate to one another.
The clearest result: direction mattered
Across the study’s measurements, horizontal spatial acuity was generally higher than vertical acuity.
The strongest differences appeared at the lower back near the spine and at the abdomen. The peripheral lower-back site showed little directional difference.
There is an important detail in that comparison: the peripheral lower-back site was tested only horizontally. Its vertical comparison used the near-spine measurement because the lateral surface did not provide enough flat area.
Even with that limitation, the larger pattern is useful.
Two vibration points can be separated by the same distance and still be easier or harder to distinguish depending on their orientation and where they contact the body.
The body is not simply asking, “How far apart are these points?” It is also reading, “In which direction are they arranged, and where on the body are they?”
The lower back was not one uniform surface
The study also found a horizontal sensitivity gradient across the lower back.
Near the spine, participants could recognize direction at smaller separations. Farther from the spine, the vibration points needed more distance between them to reach comparable recognition levels.
The authors note that this pattern is consistent with earlier research describing the body’s midline as a perceptual anchor.
That is a meaningful idea for any product intended to create a distributed physical experience: placement cannot be separated from perception.
Motor count is only part of the design
The study did not compare systems with different motor counts. But its spatial-acuity measurements show why count alone is incomplete.
If two vibration points are spaced closer than people can reliably distinguish at a given location and orientation, adding another point may not add equally distinct spatial information.
The useful question is not only, “How many vibration points are there?”
It is, “Can the body meaningfully tell them apart?”
A high component count can look impressive on paper. A coherent tactile experience also depends on spacing, orientation, body location, physical contact, timing and the signal driving the system.
Why this matters for feeling music
Music is already organized through space and time. A kick drum, bass line, vocal and string section do not behave the same way. Their rhythms, dynamics and frequency content move differently.
When music is translated into vibration, the challenge is not to make every point fire as hard as possible. It is to preserve enough structure that the physical layer belongs to the same musical event the ears are hearing.
The 2025 study did not test music or listening enjoyment. It provides useful psychophysical evidence for one engineering question underneath body-felt sound: how location, orientation and spacing affect what the body can resolve.
That makes haptic design less like installing a row of identical motors and more like designing a listening system for another sense.
Where SoundBlanket fits
SoundBlanket uses 18 haptic transducers arranged across the blanket in a 6-by-3 layout. The goal is distributed contact across the body rather than a single vibration point.
SoundBlanket was not tested in this study. The researchers used a controlled laboratory apparatus—not a blanket, music or a sleep setting.
What interests me is the design principle: the body is not an even surface, so thoughtful placement matters. Full-body haptics should be designed around perception, not only power.
That is the direction I keep returning to as we develop SoundBlanket: make the physical layer feel connected, balanced and musical—not simply stronger.
What the study leaves open
The participant group was relatively small and young. The researchers used a fixed frequency, contact force and controlled body positions.
Real-world haptics also involve clothing, padding, posture, body composition, individual sensitivity and signals that change continuously over time.
Those are not small details. They are the next design questions.
What I took away
The most important result was not that one body area is “better” than another.
It was that tactile perception has structure.
Side-to-side and up-and-down vibration are not read equally. The lower back changes from the midline outward. Adding another vibration point is only useful when the body can resolve what that point is doing.
For me, that is the opportunity in body-felt sound: not more vibration for its own sake, but a physical experience designed with the same care we already give to speakers, headphones and rooms.
— Lance
Founder, SoundBlanket
Frequently asked questions
Does every part of the body feel vibration the same way?
No. The study found that body location, direction and spacing influenced how reliably participants distinguished vibration.
What is vibrotactile spatial acuity?
It is the ability to distinguish where vibration occurs and how separate vibration points relate to one another. Higher spatial acuity means closely spaced points can be distinguished more reliably.
Does adding more vibration motors always improve a haptic system?
Not necessarily. Motor count is one design variable. Spacing, orientation, body location, contact, timing and signal design also affect what the body can distinguish.
Did this study test SoundBlanket?
No. It used a controlled laboratory apparatus with short vibration bursts at approximately 130 Hz. It did not test SoundBlanket, music, sleep or therapeutic outcomes.
Why does direction matter in haptic design?
Horizontal spatial acuity was generally higher than vertical acuity across the study’s measurements. This suggests that haptic layouts should account for orientation as well as distance.
Source
vom Stein, M., Hoppe, M., Rieger, N., & Wolf, K.-D. “Data-driven design guide for vibrotactile display layouts by continuous mapping.” Scientific Reports 15, 39579 (2025).