8 Dec 2019 ............... Length about 500 words (6,000 bytes).
(Document started on 20 Oct 2005.)
This is a WWW document maintained by
Steve Draper, installed at http://www.psy.gla.ac.uk/~steve/best/senses.html.
You may copy it.
How to refer to it.
Web site logical path:
How many senses do humans have?
Department of Psychology,
University of Glasgow.
New Scientist article, 29 Jan 2005 by Bruce Durie,
"Senses special: Doors of perception" on how many senses we have. If you are
at Glasgow University then the best way to get the link to work may be to
FIRST login to your library account an some window; THEN click the link
But in any case, Aristotle's answer of 5 is definitely wrong:
vision, hearing, touch, taste, smell.
Defensible answers are:
- 3: the number of physical types of stimulus: light (photons), chemicals
(smell, taste, and internal sensors), mechanical (touch and hearing).
- 9: vision, hearing, touch, taste, smell, pain, mechanoreception (balance
etc.), temperature, interoreceptors (e.g. blood pressure, bladder stretch).
- 21 (see table below)
Of course the real answer is that this is the wrong way to look at it.
Sensing doesn't cause perception: real perception is all about integrating
information across senses, across time, across space if you are (as is normal)
moving around partly in order to perceive better.
External chemical sensing; Senses of smell; Olfaction
Of the chemical senses of external stimuli, it (currently) appears there may
be 4 different sets of sensors:
- The taste buds on the tongue detect 5 different flavours.
But also at least two types of receptor elsewhere in the
mouth for chilli-hot, and its opposite creamy-cool-soothing.
- Most perceived taste comes from Olfaction on exhaled air
from the oral cavity.
- Olfaction by the Olfactory bulb and nerve, analysing airborne molecules
inhaled by the nose.
But there are some women with excellent olfaction but no
olfactory bulb whatever.
- Trigeminal: airborne molecules are often also detected by other sensors
in the whole nose and oral cavity, transmitted by the trigeminal nerve,
perceived as hot/cold, but combined as part of an odour percept.
- Vomeronasal: there is some but insufficient evidence, both behavioural,
anatomical, and from brain scans, that humans have a further set of detectors
which in animals respond to pheromones, whose sensing we are unconscious of
but which do affect us. (We are largely unconscious of some other things,
such as a shortage of oxygen in the air, which undoubtedly have huge effects
The theory of how olfaction works is still undecided, but it seems clear
enough that it is like colour perception in that:
a) There are a number of different receptor types
b) the same stimulus (odour molecule) reacts with several receptor types at
once; so that
c) it is the ratio (relative strength) of responses that tells a person which
odour it is, rather than having one receptor type per detectable smell.
Dogs (bloodhounds) vs. humans: sensitivity to odours 10 million to one.
Human sensitivity to a strong odour can be 9 parts per trillion.
A silkworm moth can detect a single molecule of pheromone.
There are some cases of significant differences amongst people in what
a given stimulus smells of: like "colour blindness".
Thus you cannot trust a trained expert (a perfumer on scent, or oenologist on
wine) to know what you will like, nor even what you will experience.
Leffingwell Reports vol.2 no.1
G protein molecular nanomachine
Caraway vs. spearmint
Limonene: one example of chirality
And if we go beyond humans then there are many more again: sonar in bats (and
some moths); infrared in pit vipers; ultraviolet in bees; magnetic fields
detected by some birds (and just possibly, humans too). And perhaps most
surprising to humans: the electric senses found in various fish species.
Electroreception: the detection of nearby things, particularly other fish, by
the electric field they radiate.
Active electrolocation, where a fish emits an electric field, and senses how
it is changed by nearby objects (especially other fish).
Web site logical path:
[Top of this page]