THE ROUGH GUIDE TO PSYCHOLOGYplay the sound “BA”, what you’ll actually hear is the sound “DA”. This is
because the auditory centres of your brain are influenced by information
coming from your eyes about the lip movements of the person in the
video. The result is that you experience a sound that reflects a merging
of information from both the senses. If you want to try it out, there are
plenty of examples on the Internet (for example, at tinyurl.com/4rgzyn).
Smell
We sense a smell when chemicals bind to receptors in our noses, initi-
ating a nerve signal that travels to what’s known as the olfactory bulb
(olfaction is the scientific name for smell), housed on the underside
of the front of the brain. Traditionally, humans have been thought of
as having a rather inferior sense of smell compared with many of our
mammalian cousins. However, an amusing study conducted in 2006
suggested we might have underestimated our sniffing skills. Jess Porter
and colleagues asked participants to drop to all fours to track the scent
of chocolate through grass. Just like a dog, 21 out of 32 participants were
able to track the 10-metre trail. What’s more, the researchers chose four
of these successful trackers and showed that three hours’ practice a day
for three days substantially improved their sniffing skills, such that they
became twice as fast at tracking. “Our sense of smell is less keen partly
because we put less demand on it”, said Porter at the time, “but if people
practice sniffing smells, they can get really good at it”.
Porter’s team didn’t stop there. They also wanted to see if humans
locate smells by comparing the input to our two nostrils, much as we
locate sounds by contrasting the information arriving at our two ears.
The researchers found that participants’ tracking accuracy dropped
to 36 percent with one nostril taped up compared with tracking with
both nostrils clear, suggesting that we do indeed gain useful informa-
tion about the location of smells by comparing between our nostrils.
This finding was consistent with an earlier study, conducted by the
same research team, in which a piece of breathing apparatus was used
to deliver smells selectively to just one nostril or the other. The partici-
pants’ task in this case was simply to indicate which nostril the scent had
arrived through, which they did with 75 percent accuracy – far better than
if they had simply been guessing. This suggests that some neurons in the
part of the brain that processes smells are selective for just one nostril
or the other, again confirming the idea that our sense of smell is more
sophisticated than had previously been thought.