An electronic nose to smell?
Weizmann Institute scientists have 'trained' an electronic system to
be able to predict the pleasantness of novel odours, just like a human
would perceive them - turning the popular notion that smell is
completely personal and culture-specific, on its head. In research
published in PLoS Computational Biology , the scientists argue that the
perception (observing through senses )of an odour's pleasantness is
innately hard-wired to its molecular structure, and it is only within
specific contexts that personal or cultural differences are made
apparent.
These findings have important implications for automated
environmental toxicity and malodor monitoring, fast odour screening in
the perfume industry, and provide a critical building block for the Holy
Grail of sense technology - transmitting scent digitally.
Over the last decade, electronic devices, commonly known as
electronic noses or 'eNoses,' have been developed to be able to detect
and recognise odours.
The main component of an eNose is an array of chemical sensors. As an
odour passes through the eNose, its molecular features stimulate the
sensors in such a way as to produce a unique electrical pattern - an 'odour
fingerprint' - that characterises that specific odour. Like a sniffer
dog, an eNose first needs to be trained with odour samples so as to
build a database of reference. Then the instrument can recognise new
samples of those odours by comparing the odour's fingerprint to those
contained in its database.
But unlike humans, if eNoses are presented with a novel odour whose
fingerprint has not already been recorded in their database, they are
unable to classify or recognise it.
So, a team of Weizmann scientists, led by Dr. Rafi Haddad, then a
graduate student of Prof. Noam Sobel of the Neurobiology Department and
co-supervisor Prof. David Harel of the Computer Science and Applied
Mathematics Department, together with their colleague Abebe Medhanie of
the Neurobiology Department, and Dr. Yehudah Roth of the Edith Wolfson
Medical Center, Holon, decided to approach this issue from a different
perspective. rather than train an eNose to recognise a particular odour,
they trained it to estimate the odour along a particular perceptual
axis. The axis they chose was odourant pleasantness. In other words,
they trained their eNose to predict whether an odour would be perceived
as pleasant or unpleasant, or anywhere in between.
To achieve this, the scientists first asked a group of native
Israelis to rate the pleasantness of a selection of odours according to
a 30-point scale ranging from 'very pleasant' to 'very unpleasant.' From
this dataset, they developed an 'odour pleasantness' algorithm, which
they then programmed into the eNose. The scientists then got the eNose
to predict the pleasantness of a completely new set of odours not
contained in their database against the ratings provided by a completely
different group of native Israelis. The scientists found that the eNose
was able to generalise and rate the pleasantness of novel odours it
never smelled before, and these ratings were about 80 per cent similar
to those of naive human raters who had not participated in the eNose
training phase. Moreover, if the odours were simply categorised as
either 'pleasant' or 'unpleasant,' as opposed to being rated on a scale,
it achieved an accuracy of 99 percent.
But these findings still don't determine whether olfactory perception
is culture-specific or not. With this in mind, the scientists decided to
test eNose predictions against a group of recent immigrants to Israel
from Ethiopia. The results showed that the eNose's ability to predict
the pleasantness of novel odours against the native Ethipoians' ratings
was just as good, even though it was 'tuned' to the pleasantness of
odours as perceived by native Israelis. In other words, even though
different odours have different meanings across cultures, the eNose
performed equally well across these populations. This suggests a
fundamental cross-cultural similarity in odourant pleasantness.
The scientists' findings that odour perception is hard-wired to
molecular structure and their design of an eNose that is able to
classify new odours could provide new methods for odour screening and
environmental monitoring, and may, in the future, allow for the digital
transmission of smell to scent-enable movies, games and music to provide
a more immersive and captivating experience.
ScienceDaily
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