The initial reaction of most people would be to say five unless you’re Haley Joel Osment. Unfortunately, even though we have officially described more than that for a long time, this is still the prevalent opinion that many people have.
First off, let’s quickly go through the original five that everyone knows: taste, smell, sight, hearing and touch. They are usually attributed to Aristotle who called them the five wits. We don’t really need to go into detail since most of us know what each one does. But how many are there really? Well, this is hard to say, but definitely more than five (and normally under twenty).
The problem is that even the definition of a sense is not well-established. A general definition of a sense describes it as a group of sensory cells which corresponds to a particular region of the brain and provides you with information by reacting to stimuli. Therefore, it could be argued that any reaction you experience without smelling, hearing, seeing, tasting or touching something would be the cause of another sense. With that in mind, let’s take a look at some of the other senses:
This one is definitely a sense, one we use all the time. The name is pretty suggestive – it is the ability to detect heat or cold (which isn’t really a thing, it’s just the absence of heat). For humans, this sense is handled by the skin, but there are plenty of other animals that have specialized organs for this purpose.
Let’s try a quick experiment. Close your eyes. Now move your left arm wildly in the air and leave it hanging without it touching anything else. Close your fist but leave one finger extended. Now, with your eyes still closed, use your right hand to grab that finger. Unless you are drunk, you should have no problem doing this. Even though you couldn’t see, hear, smell, taste or touch your finger (or your entire left arm, for that matter), you still knew exactly where it was. This is thanks to proprioception, a sense that tells the body the positions of its parts.
This is your sense of balance. It’s what allows you to move your body without falling over (again…unless you are drunk). It also allows you to feel acceleration and a change in direction. Say you’re in a car and you can’t see or hear anything. If it begins accelerating from 50 to 150 mph, you will definitely notice a sensation even though you might have trouble describing it. The vestibular system is an organ located in the inner ear which is responsible for this sense.
This is the sense that feels pain. Well, technically, it detects tissue or nerve damage and lets the brain know that something (or someone) is hurting the body. A lot more research needs to go into this sense before we understand it fully. It wasn’t until relatively recent that we thought that nociception was just an extension of the touch sense brought on by an overload of pressure receptors.
This is not a single sense, but rather refers to all of the internal senses which are stimulated and triggered within the body. Their exact number is a bone of contention, but some of the more important ones include systems that detect pretty important stuff such as feeling thirsty, hungry or even being suffocated.
By far the most controversial (and coolest) entry here, chronoception deals with the ability to detect the passage of time. It cannot be isolated to a single organ, but research shows that humans do, indeed, posses a sophisticated system which gives them information regarding the (perceived) duration of a particular event.