How tactile vibrations create illusions

Date:
September 23, 2021
Source:
Universite' de Gene`ve
Summary:
Among the traditional five human senses, touch is perhaps the least
studied. Yet, it is solicited everywhere, all the time, and even
more so in recent years with the widespread daily use of electronic
devices that emit vibrations. Indeed, any moving object transmits
oscillatory signals that propagate through solid substrates. Our
body detects them by means of mechanoreceptors located below
the skin and transmits the information to the brain similarly to
auditory, olfactory or visual stimuli. By studying how mice and
humans perceive tactile vibrations, researchers discovered that the
brain does not reliably perceive the frequency of a vibration when
its amplitude varies. An illusory phenomenon is thereby created,
which highlights how far our perception of the world around us
can deviate from its physical reality.



FULL STORY ========================================================================== Among the traditional five human senses, touch is perhaps the least
studied.

Yet, it is solicited everywhere, all the time, and even more so in
recent years with the widespread daily use of electronic devices that
emit vibrations.

Indeed, any moving object transmits oscillatory signals that
propagate through solid substrates. Our body detects them by means of mechanoreceptors located below the skin and transmits the information to
the brain similarly to auditory, olfactory or visual stimuli. By studying
how mice and humans perceive tactile vibrations, Swiss researchers from
the universities of Geneva (UNIGE) and Fribourg (UNIFR) discovered that
the brain does not reliably perceive the frequency of a vibration when
its amplitude varies. An illusory phenomenon is thereby created, which highlights how far our perception of the world around us can deviate
from its physical reality. The results can be discovered in the journal
Nature Communications.


========================================================================== Vibrations are small oscillatory movements emitted from a point of
equilibrium.

By propagating as waves through solid materials, they can be perceived by
most living organisms. Vibrations are defined by two principle features: frequency, which signals the rate of change in Hz (i.e. the number
of repetitions per second) and amplitude, which corresponds to the
maximal size the wave can reach, in other words its intensity. "When
for instance our phone vibrates, the vibration can vary more or less
rapidly -- its frequency -- and more or less strongly -- its amplitude," explains Daniel Huber, professor in the Department of Basic Neuroscience
at UNIGE Faculty of Medicine, who directed the study.

"How does our brain interpret these physical characteristics? This is
the question we aimed to answer in our study." Identical perception in
mice and humans To this end, the scientists performed the same experiment
in a group of mice and a group of human participants, in which they had
to differentiate multiple vibration frequencies felt on the hand or the
paw. "It turns out that mice are more sensitive to higher frequencies
(about 1000 Hz), whereas the human sensitivity is optimal in the much
lower frequency range, around 250 Hz," explains Mario Prsa, professor in
the Department of Neuroscience in the Faculty of Science and Medicine at
UNIFR and the first author of the study. "However, both mice and humans
have a harder time differentiating a lower from a higher frequency
when their amplitudes are not matched. A specific choice of their
respective amplitudes can actually create perceptual metamers: physically different frequencies that are perceptually indistinguishable. It is
quite remarkable!" This illusion follows a simple principle: frequencies
that are higher or lower than the most sensitive frequency -- 250 Hz for
humans and 1000 Hz for mice -- are felt as more similar to this preferred frequency when their amplitude is increased. In this condition, a high frequency vibration (e.g. 500 Hz) thus appears to be lower than it really
is, whereas a vibration whose frequency is lower to the preferred one
(e.g. 150 Hz) appears to be higher.

"Falling victim to this psychophysical illusion, the brain misperceives by refocusing on what it knows best" describes Mario Prsa. "Such phenomena
are also characteristic of other senses, like audition, where our own perception can be fooled by very low or high volumes and rarely represents
real physical attributes of sound, but rather a composite feature of
several stimulus characteristics." A still mysterious phenomenon How and
why is this illusion created in our brains? "This question is precisely
the subject of our ongoing work," explains Daniel Huber. "At what moment exactly does the brain fail to correctly interpret tactile stimuli, and
what happens at the neuronal level? And why do different species, like
mice and humans, misperceive in the same way?" The team of Daniel Huber
dives even further into this topic: with the help of deaf volunteers and musicians they transpose pieces of music into the range of vibrotactile
stimuli to study how deaf people can be able to perceive music.

========================================================================== Story Source: Materials provided by Universite'_de_Gene`ve. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Mario Prsa, Deniz Kilicel, Ali Nourizonoz, Kuo-Sheng Lee, Daniel
Huber. A
common computational principle for vibrotactile pitch perception
in mouse and human. Nature Communications, 2021; 12 (1) DOI:
10.1038/s41467-021- 25476-9 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210923115648.htm

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