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SMELLS that you can鈥檛 detect on their own can be clearly perceived if you
sniff and taste at the same time, say scientists in Pennsylvania. The finding
may help vindicate people who complain of unpleasant environmental odours that
tests show are below detectable levels, they say.

Scientists have known for some time that in a single sensory system such as
taste, stimuli at subthreshold levels can be detected when several are combined.
Pamela Dalton and her colleagues at the Monell Chemical Senses Center in
Philadelphia decided to test the interaction between the different senses of
taste and smell, which are integrated when people perceive flavours.

The researchers had to find an odour that couldn鈥檛 be tasted and a taste that
couldn鈥檛 be smelt. Armed with benzaldehyde, which has a cherry-almond odour, and
saccharin, a sweetener, they asked five men and five women to sniff and
taste.

Before each testing session, the researchers established thresholds for each
person below which the substances could not be detected by asking them to sniff
pairs of odours and decide which had a smell. To set taste thresholds,
volunteers had to swish saccharin and water mixtures around in their mouths for
a few seconds, then spit, rinse and report if they could taste anything.

After that the team picked even weaker, subthreshold samples to try out in
combination. This time, volunteers had to slosh the solution around in their
mouths and sniff the odour at the same time.

Combining taste and smell made the odour much more obvious, they found. 鈥淭en
minutes before, they hadn鈥檛 been able to detect it,鈥� says Dalton. On average,
the researchers report, the benzaldehyde thresholds were 28 per cent lower when
combined with saccharin.

Next Dalton鈥檚 team decided to mix the savoury taste of monosodium glutamate
with the cherry-almond smell of benzaldehyde鈥攏ot a common combination in
North America. This time detection improved in only one of the volunteers, and
he was from Japan, where this particular taste-smell combination is popular.
Dalton says this shows that experience may play an important role in fine-tuning
our perceptions.

The study suggests that people, like cats and primates, have 鈥渕ultisensory鈥�
neurons鈥攏erve cells that are uniquely responsive to sensory combinations,
such as smell and taste, or vision and touch. It also may explain why
environmental assessors often can鈥檛 find the source of unpleasant workplace
odours or tastes. 鈥淭he individual components may well be below the threshold
when measured,鈥� says Dalton, 鈥渂ut the brain may be putting these things
迟辞驳别迟丑别谤.鈥�