Web Design for All the Senses

My friend, Nathan Shedroff, provides many foundations and definitions for the discipline of experience design in his book experience design 1:

“Most technological experiences—including digital and, especially, online experiences—have paled in comparison to real-world experiences and have been relatively unsuccessful as a result. What these solutions require is for developers to understand what makes good experiences first, and then to translate these principles, as well as possible, into the desired media without the technology dictating the form of the experience.”

It is amusing to me that the experience design community often self-identifies as being Web or digitally focused, but as Nathan points out, design for the Web is drastically behind other media in creating a truly experiential interaction.

Of course, much of that has to do with the nature of digital media. The technology and interface opportunities do not lend themselves to obvious and easy implementation of multi-sensorial experiences. However, that is ultimately a challenge and not a true barrier. As Nathan alludes, the real reason the Web and other digital networks and interactions are such a hollow, flat experience is we are not being innovative and creative enough. Happily, this is something that we can easily take control of and change.

Experience design requires that we design for all five senses. It is safe to say that over 99% of what is happening on the Web relates only to our sense of sight. On the surface, this might seem a logical and obvious state of affairs. In reality, it is a reflection of some mental laziness and of not thinking outside the computer screen. Let’s look at each of the other four senses and explore how we can integrate design for those senses into our Web experiences:

Hearing

Our sense of hearing is the only other primary sense regularly stimulated within the Web experience. This happens in three basic ways:

Business need

Hearing is essential to some businesses and products, and they have innovated on the Web to create opportunities for people to hear what they have to offer. Certainly, the meteoric rise of the original Napster, and more recent success of Apple’s iTunes and related products and peripherals, is a testament to auditory content on the Web.

Without the ability to listen on the Web in the first place, we would not have reached the point where people will not just buy downloadable music on the Web but even purchase it without having heard it first. It was the free and easy availability of real music and online content that enabled this industry to spark, sizzle, and finally burn. The iPod is the hottest consumer electronics product because of the evolution from early music availability into major pent-up market need. Markets find a way.

The music industry is one example of the business model and auditory nature of the product driving the integration of stimulating this human sense onto the Web.

Multimedia integration

ESPN, once the leading television sports channel, has become a Disney-owned multimedia superpower with significant content and reach across many cable channels, an international radio network, a major print publication, and one of the larger and more substantial news-related Web sites in the world. ESPN.com represents the fulcrum for integrating and leveraging the corporation’s entire media empire.

Over the last two years ESPN has quietly moved into making the Web a true extension of its traditional media base—television—by staying at the front edge of online video technology. One component of that is sound. Because of their business goals and the need to maximize the effectiveness of other media, espn.com has a deep integration of auditory opportunities on their site, ranging from radio feeds to television segment re-broadcasts to clips from sporting events and more.

Design sensibility

Some Web experiences prominently integrate sound for the purpose of defining the sensibility and aesthetic of the site owner, for the enjoyment of those interacting with the site, or both.

One of my favorite examples of this in practice is a little Web design company in the Washington, D.C., area: michelango.com. I first stumbled upon this site some five years ago, and it still represents to me what the best use of sound on the Web is all about: subtle, effective, integrated into the visual design and integrated into the vibe, identity, and brand of the company itself.

Another common way to integrate sound is through content sampling or sharing. Digital Web Magazine’s own D. Keith Robinson does this on his site Asterisk with Song of the Week. Keith has integrated a self-contained media player onto his site and regularly writes a review of different songs he’s listening to, making those songs available on the site. Particularly for a blog or other form of personal publishing, expression, and communication, this sort of content sharing and sensorial integration is natural, and weaves a tighter relationship between the site owner and the visitors they share the most in common with. As with michelangelo.com, Keith’s success is the product of strong and logical execution as much as simply making auditory content available.

I am not saying that integrating sound into your Web design is easy—on the contrary. One of the reasons we see so few examples of sound design on the Web is the large volume of spectacular failures we were saturated with during the Internet boom. Sites forced auditory content at us that was poorly conceived and executed, typically by people delighted with the powerful tools at their disposal, but without the design sensibility or capability to use them properly.

As the Web has become more refined, the reverse has become true. Sound is not being properly integrated to create better sensorial experiences. By thinking about the reasons sound has been aggressively integrated into Web experiences, and examining these and other examples of it being done successfully, we can rather easily bring the stimulation of this important sense into our own strategy and design.

Smell

There is so much the Web design industry can learn from the movie industry. Ever heard of Smell-O-Vision? Understanding the power of multi-sensorial experiences, the movie industry experimented—more than 40 years ago now—with integrating olfactory experiences into movie viewing. Unfortunately, the technology was not equal to the idea, and the experience was poor.

Fast forward to the 21st century, and a new and improved Smell-O-Vision. While the technology is still in the experimental stage—far from mainstream—it reflects an understanding of the untapped business potential available through an integration of the sense of smell. For some companies, this is a no-brainer. The fragrance industry would greatly benefit from this technology. Flowers and food are other products that lend themselves to aggressively exploring and making the most of this technology. But good experiences go much farther than business need. There are plenty of pleasant, mainstream, inoffensive smells that I would enjoy “sharing” with visitors to my own site—just very slightly, very lightly, the most brief and subtle of gentle whiffs, to evoke a smile or thoughtful tilt of the head.

This updated Smell-O-Vision holds great promise because of the deep understanding we now have of olfactory science. Organizations like the Sense of Smell Institute will be of increasing interest to business and, by extension, to Web and experience design.

Smells can be broken down into just a handful of component parts, and appropriate replication of smell through a digital device is a very real possibility. We’ll see what happens with Smell-O-Vision, but it is only a matter of time now before some technology enables us to easily indulge in integrating olfactory stimulation into our digital experiences.

Even now, there are other ways we can integrate the sense of smell into our design and development. Smell is particularly important in design, since it’s the sense most directly tied into our memory. Let’s look at the last two senses to better understand how we can integrate smell into our design today.

Touch

How can we design for touch on the Web? It seems impossible. But that barrier was imposed on us by old paradigms, and is no longer right or valid.

First, we need to remember that every single person interacting with our Web experiences is stimulating their sense of touch. They are typing on a keyboard, or moving and clicking a mouse, or using a stylus, or pushing buttons or… something. Touch already is a part of the experience, but it is one that is controlled by hardware manufacturers and not something that we consider within our provenance or sphere of control. But it can be within our control if we want it to be.

Second, we need to get our heads (not to mention our asses) out from behind our digital interfaces. Designing an experience is holistic. It is not limited to pictures or sounds or pixels or hardware. We need to assert ourselves into the environments of the people interacting with our Web experiences. The interaction does not need to end with the Web or interface, even if it is centered there.

This exercise is a little bit easier for me, because before I moved over to the creative and design side of the business I was a marketing strategist. One of my responsibilities was to innovate how we could best communicate to customers and the market. What media channels could we take advantage of? How could we best leverage those channels to have the biggest possible impact? Designers and developers should be thinking the same way.

Specific applications will depend on the company, product, or site goal we each have to deal with, but in any case it’s oh, so logical. For companies that rely on touch and feel for sales—the fashion industry for instance—it is essential to get materials in the hands of customers.

A common tactic is to drive people to the Web through traditional marketing, such as running a television commercial that also attempts to get people onto the site. But this can just as easily run in reverse. Instead of the traditional marketing channel being the driver, the Web can become the driver.

Direct mail is a great example. Why not send people a small piece of fabric that can attach to their mouse, monitor, or keyboard, specifically to influence their Web experience? This way, not only can they interact with and touch the product while on your site, they can do so when using other sites. And this area is ripe to be taken advantage of!

Sit back from your monitor a little bit. Stop clicking. Look around. What in your environment, while you are interacting with your computer, is designed to stimulate your sense of touch? I’m guessing that very few of us have anything like that available. Yet, if available, every single time I gently rubbed a piece of trademark Burberry or branded cashmere, the company or product that introduced that tactile interaction into my overall Web experience would benefit from it. I might be on the CNN site being bombarded by expensive ads from big companies, but I’ll be gently rubbing that little piece of fabric and warmly appreciating the company that was thoughtful enough to put it there, rather than the advertisers.

It is just basic experience design—think beyond the specific media and create a better overall experience.

Taste

This is the toughest of the five senses to design for. In approach, it is rather similar to touch or smell. Yet, unlike other senses, taste is not a continuous part of our everyday life. We access taste only at specific times—at meals or other ritualistic personal behaviors such as coffee drinking—and it is almost always a matter of our own control.

Sights and sounds and smell and even touches are more often than not imposed upon us from the outside. They are not invited in; we are presented with them and left to interpret, categorize, and respond to them in the way we best see fit. As such, the challenge of designing for taste requires subtle modifications to basic behavior, as well as basic ideation and implementation.

Chewing gum and mints are two examples of products that began to break the limited paradigm of taste. People will use these products all day long, stimulating their sense of taste in an ongoing way. In fact, this entire product category is ultimately ripe for buy-outs from and subordination by major brands that have nothing to do with the core products (Harley-Davidson gum, anyone?) but that is beyond the bounds of this article and publication.

People love to eat, and they enjoy having their sense of taste stimulated. I give a lot of presentations and seminars, and most of the time I make sure to hand out to the entire audience some sort of a small taste treat during the course of my talk. The effect of doing this is remarkable. People smile. Their body language changes. Their energy level changes. By providing just these little, inexpensive treats, it creates an entirely different moment and interaction. That is powerful!

Since very few non-food-related companies currently have any sort of a taste associated with them, the best way to design for taste is to design for the end user. What sort of things do people like? When and why do they like them? What connections can we draw between our company/products/selves and those particular tastes or items? How can we get those to the people?

These aren’t your typical development questions, and certainly not appropriate for all situations, but this is the way we need to be thinking. We are designing experiences, not just Web sites. Taste is an important part of experience. We need to think about that, even if we are only supposed to be thinking about boxes and buttons and pixels.

Ours to design

It certainly isn’t rocket science. It is just a matter of opening our minds up a little bit and taking a new look at our definitions and boundaries. After that, the only limitations are imposed by our creativity.

Technological and financial barriers are factors, not impediments. And the benefits of creating better experiences are virtually limitless. Just think to yourself: What are the things I am most passionate about or moved by? Most often, the answers lie in areas not currently being addressed within design solutions, yet well within our individual grasp to provide. The world is ours to design, and there is no reason to wait.

http://www.digital-web.com/articles/web_design_for_all_the_senses/

The Smell Report

The human sense of smell

Although the human sense of smell is feeble compared to that of many animals, it is still very acute. We can recognise thousands of different smells, and we are able to detect odours even in infinitesimal quantities.

Our smelling function is carried out by two small odour-detecting patches – made up of about five or six million yellowish cells – high up in the nasal passages.

For comparison, a rabbit has 100 million of these olfactory receptors, and a dog 220 million. Humans are nonetheless capable of detecting certain substances in dilutions of less than one part in several billion parts of air. We may not be able to match the olfactory feats of bloodhounds, but we can, for example, ‘track’ a trail of invisible human footprints across clean blotting paper.

The human nose is in fact the main organ of taste as well as smell. The so-called taste-buds on our tongues can only distinguish four qualities – sweet, sour, bitter and salt -all other ‘tastes’ are detected by the olfactory receptors high up in our nasal passages.

Variations

Our smelling ability increases to reach a plateau at about the age of eight, and declines in old age. Some researchers claim that our smell-sensitivity begins to deteriorate long before old age, perhaps even from the early 20s. One experiment claims to indicate a decline in sensitivity to specific odours from the age of 15! But other scientists report that smelling ability depends on the person’s state of mental and physical health, with some very healthy 80-year-olds having the same olfactory prowess as young adults. Women consistently out-perform men on all tests of smelling ability (see Sex differences).

Schizophrenics, depressives, migraine sufferers and very-low-weight anorexics often experience olfactory deficits or dysfunctions. One group of researchers claims that certain psychiatric disorders are so closely linked to specific olfactory deficits that smell-tests should be part of diagnostic procedures. Zinc supplements have been shown to be successful in treating some smell and taste disorders.

Although smoking does not always affect scores on smell-tests, it is widely believed to reduce sensitivity.

A recent study at the University of Pennsylvania suggests that, contrary to popular belief, blind people do not necessarily have a keener sense of smell than sighted people. In their experiments on blind and sighted people, the top performers on most tests were (sighted) employees of the Philadelphia Water Department who had been trained to serve on the Department’s water quality evaluation panel. The researchers conclude that training is the factor most likely to enhance performance on smell tests. (University of Pennsylvania researchers are probably fairly clued-up on this subject – they designed the University of Pennsylvania Smell Identification Test (UPSIT) which is the standard test used in almost all experiments.)

The importance of ‘training’ in the development of smell-sensitivity is confirmed by many other studies. Indeed, this factor can sometimes be a problem for researchers, as subjects in repetitive experiments become increasingly skilled at detecting the odours involved.

Smell-sensitivity researchers have to be very careful about the odours they use in experiments, because a smell is not always a smell. Many odorous substances activate not only the olfactory system but also the ‘somatosensory’ system -the nerve endings in our noses which are sensitive to temperature, pain etc. This is why ‘anosmics’ – patients who have completely lost their sense of smell – can still detect menthol, phenylethyl alcohol and many other substances. In a study testing anosmics’ ability to perceive odorous substances, it was found that many so-called odours are in fact affecting the pain- and temperature-sensitive nerve-endings, rather than the olfactory receptors. Out of 47 ‘odorous’ substances, anosmics could detect 45. (Only two substances could not be detected by the anosmic patients: these were decanoic acid and vanillin, which affect only the olfactory receptors, and can thus safely be classified as ‘pure’ odours.) Some unpleasant ‘smells’ do more than just annoy or disgust us, they actually cause us pain.

Children

Although smell-identification ability increases during childhood, even newborn infants are highly sensitive to some important smells: recent research shows that newborn babies locate their mothers’ nipples by smell. In experiments, one breast of each participating mother was washed immediately after the birth. The newborn baby was then placed between the breasts. Of 30 infants, 22 spontaneously selected the unwashed breast.

Other experiments have also shown that babies are responsive to very faint differences in body odour, but it is believed that infants are highly sensitive only to specific smells, rather than a wide range of odours.

In terms of odour preference, however, one significant study showed that 3-year-olds have essentially the same likes and dislikes as adults. Experiments conducted in the early 70s and replicated in 1994 revealed that children do not develop sensitivity to certain odours until they reach puberty. In these studies, 9-year-olds showed a pronounced insensitivity to two musk odours, although their ability to detect other odours was the same as that of postpubescents and adults.

http://www.sirc.org/publik/smell_human.html

Your Sense of Smell

What are smells?
What makes the smell of something, like, say, rotten eggs? While what’s making the smell may be invisible to the naked eye, it doesn’t mean there’s nothing there! The smell is just made of things too small to see. You know they’re there because you can smell them.

Odors are tiny molecules of chemicals from things like food, or flowers or poop that float through the air. Many odors aren’t single scents or single kinds of molecules but a whole mixture of them.

How do we smell smells?
Through your nose. It’s a mucus-covered, twisty cavern that’s built to smell as well as warm, moisten, and filter the air you breath. When you breath through your nose, air enters both of your nostrils. Hairs, hanging from the walls of each opening, act as filters trapping dirt, dust, pollen — all sorts of things — even bugs!

As the air moves further back inside your nose, the locale gets warmer and slimier. There’s wet mucus everywhere! And if you look carefully, you discover the mucus is actually moving. Incredibly, small hair-like structures called cilia are sweeping or undulating back and forth, moving the mucus (and anything trapped in it) further and further back. At the same time, the air moving back is warmed by blood vessels just beneath the surface, filled with warm, pulsing blood.

As the air spirals around, bouncing off ridges and valleys, the passageway opens up to a big cavern — your nasal cavity. Rivulets of mucus stream back and down into our throat. You swallow a lot of it!

The odor chemicals that you inhaled, on the other hand, begin to float upward, not downward. They hit a ceiling area in your nasal cavity. About the size of a postage stamp, it’s covered with millions upon millions of microscopic nerve cells that can detect smell. Odor molecules sink through a thick, mustard-colored mucus until they reach the sensitive hair-like tops of the nerve cells and get trapped. Differently shaped nerve cells recognize different smells because each smell molecule fits into a nerve cell like a lock and key. Then, these cells send signals along your olfactory nerve to the smell center in your brain. It senses the odor or collection of odors. Does it smell bad or good? Now that all depends on you and your sense of smell.

What’s the connection between smell and taste?
Most of your sense of taste is really about your sense of smell. Do you think that the spaghetti and meatballs you’re eating taste delicious? Much of the reason is because you like their smell. In fact, you’re doing a lot of sniffing. Not only are you smelling before you take a bite, but while you are chewing, odor molecules from the ground-up food inside your mouth float upwards taking that remarkable smell journey.

Factoids

• If your sniffer is in peak performance you can tell the difference between 4000-10,000 smells. Now that’s heavy-duty sniffing!
• WARNING: As you grow older, your sense of smell gets worse. Children are likely to have much more subtle senses of smell than parents or grandparents.
• MAYBE YOU WANT TO BE BLOODHOUND? They smell at least 1000 times better than humans.
• MAYBE YOU WANT TO BE A MALE MOTH? Just a dozen odor molecules from a lady moth a block away can drive a male moth crazy!
• BE GLAD YOU’RE NOT A DOLPHIN OR WHALE — Instead of two nostrils in the middle of your face, you’d have one blowhole on the top of your head!

http://yucky.discovery.com/flash/body/pg000150.html

Sense of Sight

Imagine this: it’s early morning. No sounds. No smells. But open your eyes and, as long as there is light, there is always something to see. From the moment you wake up in the morning, until the moment you go to sleep, your eyes are taking in information and relaying it to your brain to interpret! Of all the senses, sight is the richest and most complex.

Look Closely
Sit a friend or family member down and look into one of their eyes. The first thing you’ll notice is that the eye sits in a hollow space in the skull and is protected by an eyelid and a bony eyebrow. As you gaze deeply into the eye, you look through the transparent, curved cornea to the donut-shaped ring called the iris, sitting in the center of the white of the eye. The iris is the part that can vary from blue, to brown to hazel and determine eye color. It’s also the part whose muscles cause the pupil, the dark circle in the center, to enlarge or contract.

It’s through the pupil that light rays enter the eyeball. The size of the pupil changes depending upon the light available. Just behind the pupil is the lens. It’s the transparent part of the eye which bends those rays of light and focuses the image on the back surface of the eyeball. How? With the help of muscles that actually change the shape of the lens!

Looking at something close up? The lens will become thicker. Admiring something that’s far away? Muscles will squeeze the lens, making it thinner so that you can see the image clearly. Remarkable, don’t you think?

Once the light travels through the lens, it must still travel through lots of clear jelly, called the vitreous humor, which makes up most of the eye. But, finally, the light makes it to the back surface, or retina, of the eye.

130 Million Light-Sensitive Cells
The retina, about the size of a postage stamp, is filled with two different kinds of light-sensitive cells — 130 million of them! Rods register shapes and respond to low levels of light. Cones, on the other hand, register color and only work in bright light (which is why colors become harder to see as it gets darker). Then, through optic nerves, these light-sensitive cells send information to the brain.

What about the images that are being communicated to the brain?
Remarkably, the images shining onto the retina and also being communicated to the brain are upside down! It’s the brain’s job, not the eye’s, to translate those upside-down images and interpret the information it receives into visual meaning that you can understand.

Why do people sometimes need glasses?
Sometimes the lenses in peoples’ eyes don’t properly focus light on the back of the retina. If an eyeball is too short, the image will fall behind the retina. People are then called far-sighted, because their eyes can focus on things far away but not close up. If, on the other hand, an eye is too long, people see things nearby but not far off and are called near-sighted. Either way, glasses or contact lenses can generally enable them to see much better!

Factoids

• You may think humans have good eyesight but imagine being an owl. An owl can see a mouse moving over 150 feet away with light no brighter than a candle!
• A cat’s eyes glow in the dark because of special silvery “mirrors” that reflect light, making it much easier for them to see in the dark.
• So-called “color-blindness,” in which colors such as green and red are hard to distinguish, affects about 1 in 30 people — and many times more men than women!

http://yucky.discovery.com/flash/body/pg000142.html

How Touching Works

Introduction to How Touching Works

After a long day at work, you walk in the door and slip off those toe-pinching, heel-blistering shoes. You quickly give yourself a therapeutic rub down and then slip into some warm, fuzzy socks. You give your dog a quick pat, grab a soft pillow and finally flop down on the couch. About the time you get into a comfortable position, you realize you set your drink a bit too far away on the table. This isn’t a problem, though. While you focus your attention on the TV screen, you reach over and feel around for your hot cup of tea. Once your hand hits the warm ceramic mug, you realize you’re home.

Not more than 15 minutes has passed since you walked through the door, but your sense of touch has gathered millions of bits of information from your surroundings. The pain from your pair of shoes is gone, and soft, fluffy comfort has taken over. A cold, wet kiss from your dog has given way to the warm comfort of the couch and a cup of hot tea. From temperature to texture, your sense of touch has been in constant communication with your brain.

Your somatic sensory system is responsible for your sense of touch . The somatic sensory system has nerve receptors that help you feel when something comes into contact with your skin, such as when a person brushes up against you. These sensory receptors are generally known as touch receptors or pressure receptors. You also have nerve receptors that feel pain and temperature changes such as hot and cold .

If you want to learn more about this complex system, read on to find out how your sense of touch works from head to toe and back again.

Physiology of Touching

You probably think of the sense of touch as relating to your skin. After all, you have about 5 million sensory nerve receptors in your skin. But you also can feel pain and pressure inside your body. Think about stomachaches and headaches. Most of your sense of touch, though, comes from external stimulus by way of your skin.

So how does a quick journey from the touch receptors in your skin to your brain happen? When the touch, pain or heat sensors in your skin are stimulated, they send electrical pulses to your neurons, special cells that relay electrochemical impulses . The sensory neurons then act as a relay team, passing along the electrical pulse from neuron to neuron until it reaches your spinal cord. Your spinal cord takes the incoming signal and sends it to your brain. Once the brain receives the signal from the spinal cord, it translates the electrical signal .

If your pain receptors have sent a message saying that a pair of tight-fitting shoes has gotten too uncomfortable, the brain knows your body is feeling pain. Your brain signals the muscles in your foot to curl up your pinkie toe away from the pain until you take your shoes off. If you’ve touched something very cold, your brain knows the cold receptors have been activated; you’ll probably shiver in response. Likewise, if you are feeling pressure when you hug an old friend, your brain will sense the pressure of the hug around your shoulders or body.

Your brain can combine messages from your sensory receptors. For instance, when you wrap a heated cotton towel around your body after stepping out of the sauna, you’re using both your pressure and temperature receptors. However, how you feel about that action is because of the psychology behind your sense of touch. Read on to find out how your brain might perceive incoming touch in different ways.

Psychology of Touching

You probably already know a hug from a loved one can lower your blood pressure and make you feel valued and important. A firm handshake with a friend can create a connection. How you perceive the hug or handshake, along with how your touch receptors receive the pressure, is rooted in your brain.

There are several basic kinds of touch that you may experience:

• Intimate — Here, your pressure receptors respond to a handshake, hug or kiss. If the person giving the touch is someone you care about, you’ll probably feel warm and comforted. Your pressure sensors send the feeling of how hard the embrace is, and your brain interprets the nature of the touch as soothing .
• Healing or therapeutic — This type of touch is often associated with massage or acupuncture. Sometimes, the pressure is gentle and meant to soothe sore muscles. Other times, the pressure is deep in order to work out knots. Despite differences in severity of pressure, you likely to be aware that the outcome is healing, so your body allows you to relax.
• Exploratory or inquisitive — We all learn about the world through our sense of touch. Many people test out foods, fabrics or other objects by feeling different textures. Sometimes it’s possible to rely solely on the sense of touch. This is why it’s easy for you to reach into your bag and find a pair of keys without looking. You know the cold feeling of the metal key and hard smooth feel of your plastic key chain.
• Aggressive or painful — Of course, we all know that touch can also equate to pain if the pressure is too much and the intent is wrong. A handshake that’s too firm can be uncomfortable instead of reassuring.

Cicero, Shannon.  “How Touching Works.”  20 August 2009.  HowStuffWorks.com. <http://health.howstuffworks.com/skin-care/information/anatomy/touching.htm&gt;  25 December 2009.

Senses

Senses are the physiological methods of perception. The senses and their operation, classification, and theory are overlapping topics studied by a variety of fields, most notably neuroscience, cognitive psychology (or cognitive science), and philosophy of perception. The nervous system has a specific sensory system, or organ, dedicated to each sense.

Definition

There is no firm agreement among neurologists as to the number of senses because of differing definitions of what constitutes a sense. One definition states that an exteroceptive sense is a faculty by which outside stimuli are perceived.^[1] The traditional five senses are sight, hearing, touch, smell, taste: a classification attributed to Aristotle.^[2] Humans are considered to have at least five additional senses that include: nociception (pain), equilibrioception (balance), proprioception & kinaesthesia (joint motion and acceleration), sense of time, thermoception (temperature differences), with possibly an additional weak magnetoception (direction)^[3], and six more if interoceptive senses (see other internal senses below) are also considered.

One commonly recognized categorisation for human senses is as follows: chemoreception; photoreception; mechanoreception; and thermoception. This categorisation has been criticized as too restrictive, however, as it does not include categories for accepted senses such as the sense of time and sense of pain.

Different senses also exist in other animals, for example electroreception.

A broadly acceptable definition of a sense would be “A system that consists of a group of sensory cell types that responds to a specific physical phenomenon, and that corresponds to a particular group of regions within the brain where the signals are received and interpreted.” Disputes about the number of senses typically arise around the classification of the various cell types and their mapping to regions of the brain.

Sight

Sight or vision is the ability of the brain and eye to detect electromagnetic waves within the visible range (light) which is why people see interpreting the image as “sight.” There is disagreement as to whether this constitutes one, two or three senses. Neuroanatomists generally regard it as two senses, given that different receptors are responsible for the perception of colour (the frequency of photons of light) and brightness (amplitude/intensity – number of photons of light). Some argue^{[citation needed]} that stereopsis, the perception of depth, also constitutes a sense, but it is generally regarded as a cognitive (that is, post-sensory) function of brain to interpret sensory input and to derive new information. The inability to see is called blindness.

Hearing

Hearing or audition is the sense of sound perception. Since sound is vibrations propagating through a medium such as air, the detection of these vibrations, that is the sense of the hearing, is a mechanical sense because these vibrations are mechanically conducted from the eardrum through a series of tiny bones to hair-like fibers in the inner ear which detect mechanical motion of the fibers within a range of about 20 to 20,000 Hertz,^[4] with substantial variation between individuals. Hearing at high frequencies declines with age. Sound can also be detected as vibrations conducted through the body by tactition. Lower frequencies than that can be heard are detected this way. The inability to hear is called deafness.

Taste

Taste or gustation is one of the two main “chemical” senses. There are at least four types of tastes^[5] that “buds” (receptors) on the tongue detect, and hence there are anatomists who argue^{[citation needed]} that these constitute five or more different senses, given that each receptor conveys information to a slightly different region of the brain^{[citation needed]}. The inability to taste is called ageusia.

The four well-known receptors detect sweet, salt, sour, and bitter, although the receptors for sweet and bitter have not been conclusively identified. A fifth receptor, for a sensation called umami, was first theorised in 1908 and its existence confirmed in 2000^[6]. The umami receptor detects the amino acid glutamate, a flavour commonly found in meat and in artificial flavourings such as monosodium glutamate.

Note: that taste is not the same as flavour; flavour includes the smell of a food as well as its taste.

Smell

Smell or olfaction is the other “chemical” sense. Unlike taste, there are hundreds of olfactory receptors, each binding to a particular molecular feature. Odor molecules possess a variety of features and thus excite specific receptors more or less strongly. This combination of excitatory signals from different receptors makes up what we perceive as the molecule’s smell. In the brain, olfaction is processed by the olfactory system. Olfactory receptor neurons in the nose differ from most other neurons in that they die and regenerate on a regular basis. The inability to smell is called anosmia. Some neurons in the nose are specialized to detect pheromones.

Touch

Touch, also called tactition or mechanoreception, is a perception resulting from activation of neural receptors, generally in the skin including hair follicles, but also in the tongue, throat, and mucosa. A variety of pressure receptors respond to variations in pressure (firm, brushing, sustained, etc). The touch sense of itching caused by insect bites or allergies involves special itch-specific neurons in the skin and spinal cord.^[7] The loss or impairment of the ability to feel anything touched is called tactile anesthesia. Paresthesia is a sensation of tingling, pricking, or numbness of the skin that may result from nerve damage and may be permanent or temporary.

Balance and acceleration

Balance, equilibrioception, or vestibular sense is the sense which allows an organism to sense body movement, direction, and acceleration, and to attain and maintain postural equilibrium and balance. The organ of equilibrioception is the vestibular labyrinthine system found in both of the inner ears. Technically this organ is responsible for two senses of angular momentum and linear acceleration (which also senses gravity), but they are known together as equilibrioception.

The vestibular nerve conducts information from the three semicircular canals corresponding to the three spatial planes, the utricle, and the saccule. The ampulla, or base, portion of the three semicircular canals each contain a structure called a crista. These bend in response to angular momentum or spinning. The saccule and utricle, also called the “otolith organs”, sense linear acceleration and thus gravity. Otoliths are small crystals of calcium carbonate that provide the inertia needed to detect changes in acceleration or gravity.

Temperature

Thermoception is the sense of heat and the absence of heat (cold) by the skin and including internal skin passages, or rather, the heat flux (the rate of heat flow) in these areas. There are specialized receptors for cold (declining temperature) and to heat. The cold receptors play an important part in the dogs sense of smell, telling wind direction, the heat receptors are sensitive to infrared radiation and can occur in specialized organs for instance in pit vipers. The thermoceptors in the skin are quite different from the homeostatic thermoceptors in the brain (hypothalamus) which provide feedback on internal body temperature.

Kinesthetic sense

Proprioception, the kinesthetic sense, provides the parietal cortex of the brain with information on the relative positions of the parts of the body. Neurologists test this sense by telling patients to close their eyes and touch the tip of a finger to their nose. Assuming proper proprioceptive function, at no time will the person lose awareness of where the hand actually is, even though it is not being detected by any of the other senses. Proprioception and touch are related in subtle ways, and their impairment results in surprising and deep deficits in perception and action. ^[8]

Pain

Nociception (physiological pain) signals near-damage or damage to tissue. The three types of pain receptors are cutaneous (skin), somatic (joints and bones) and visceral (body organs). It was previously believed that pain was simply the overloading of pressure receptors, but research in the first half of the 20th century indicated that pain is a distinct phenomenon that intertwines with all of the other senses, including touch. Pain was once considered an entirely subjective experience, but recent studies show that pain is registered in the anterior cingulate gyrus of the brain.^[9]

Other internal senses

An internal sense or interoception is “any sense that is normally stimulated from within the body”.^[10] These involve numerous sensory receptors in internal organs, such as stretch receptors that are neurologically linked to the brain.

• Pulmonary stretch receptors are found in the lungs and control the respiratory rate.
• Cutaneous receptors in the skin not only respond to touch, pressure, and temperature, but also respond to vasodilation in the skin such as blushing.
• Stretch receptors in the gastrointestinal tract sense gas distension that may result in colic pain.
• Stimulation of sensory receptors in the esophagus result in sensations felt in the throat when swallowing, vomiting, or during acid reflux.
• Sensory receptors in pharynx mucosa, similar to touch receptors in the skin, sense foreign objects such as food that may result in a gag reflex and corresponding gagging sensation.
• Stimulation of sensory receptors in the urinary bladder and rectum may result in sensations of fullness.
• Stimulation of stretch sensors that sense dilation of various blood vessels may result in pain, for example headache caused by vasodilation of brain arteries.

Non-human senses

Analogous to human senses

Other living organisms have receptors to sense the world around them, including many of the senses listed above for humans. However, the mechanisms and capabilities vary widely.

Echolocation

Certain animals, including bats and cetaceans, have the ability to determine orientation to other objects through interpretation of reflected sound (like sonar). They most often use this to navigate through poor lighting conditions or to identify and track prey. There is currently an uncertainty whether this is simply an extremely developed post-sensory interpretation of auditory perceptions or it actually constitutes a separate sense. Resolution of the issue will require brain scans of animals while they actually perform echolocation, a task that has proven difficult in practice. Blind people report they are able to navigate by interpreting reflected sounds (esp. their own footsteps), a phenomenon which is known as human echolocation.

Smell

Among non-human species, dogs have a much keener sense of smell than humans, although the mechanism is similar. Insects have olfactory receptors on their antennae.

Vision

Cats have the ability to see in low light due to muscles surrounding their irises to contract and expand pupils as well as the tapetum lucidum, a reflective membrane that optimizes the image. Pitvipers, pythons and some boas have organs that allow them to detect infrared light, such that these snakes are able to sense the body heat of their prey. The common vampire bat may also have an infrared sensor on its nose.^[11] It has been found that birds and some other animals are tetrachromats and have the ability to see in the ultraviolet down to 300 nanometers. Bees and dragonflies^[12] are also able to see in the ultraviolet.

Balance

Ctenophora have a balance receptor (a statocyst) that works very differently from the mammalian’s semi-circular canals.

Not analogous to human senses

In addition, some animals have senses that humans do not, including the following:

• Electroception (or electroreception) is the ability to detect electric fields. Several species of fish, sharks and rays have the capacity to sense changes in electric fields in their immediate vicinity. Some fish passively sense changing nearby electric fields; some generate their own weak electric fields, and sense the pattern of field potentials over their body surface; and some use these electric field generating and sensing capacities for social communication. The mechanisms by which electroceptive fish construct a spatial representation from very small differences in field potentials involve comparisons of spike latencies from different parts of the fish’s body.

The only order of mammals that is known to demonstrate electroception is the monotreme order. Among these mammals, the platypus^[13] has the most acute sense of electroception.

Body modification enthusiasts have experimented with magnetic implants to attempt to replicate this sense,^[14] however in general humans (and probably other mammals) can detect electric fields only indirectly by detecting the effect they have on hairs. An electrically charged balloon, for instance, will exert a force on human arm hairs, which can be felt through tactition and identified as coming from a static charge (and not from wind or the like). This is however not electroception as it is a post-sensory cognitive action.

• Magnetoception (or magnetoreception) is the ability to detect fluctuations in magnetic fields and is most commonly observed in birds, though it has also been observed in insects such as bees. Although there is no dispute that this sense exists in many avians (it is essential to the navigational abilities of migratory birds), it is not a well-understood phenomenon.^[15] One study has found that cattle make use of magnetoception, as they tend to align themselves in a north-south direction.^[16] Magnetotactic bacteria build miniature magnets inside themselves and use them to determine their orientation relative to the Earth’s magnetic field.^{[citation needed]}

• Pressure detection uses the organ of Weber, a system consisting of three appendages of vertebrae transferring changes in shape of the gas bladder to the middle ear. It can be used to regulate the buoyancy of the fish. Fish like the weather fish and other loaches are also known to respond to low pressure areas but they lack a swim bladder.

• Current detection The lateral line in fish and aquatic forms of amphibians is a detection system of water currents, mostly consisting of vortices. The lateral line is also sensitive to low frequency vibrations. The mechanoreceptors are hair cells, the same mechanoreceptors for vestibular sense and hearing. It is used primarily for navigation, hunting, and schooling. The receptors of the electrical sense are modified hair cells of the lateral line system.

• Polarized light direction/detection is used by bees to orient themselves, especially on cloudy days. Cuttlefish can also perceive the polarization of light. Most sighted humans can in fact learn to roughly detect large areas of polarization by an effect called Haidinger’s brush, however this is considered an entoptic phenomenon rather than a separate sense.

• Slit sensillae of spiders detect mechanical strain in the exoskeleton, providing information on force and vibrations.

taken from wikipedia: senses