On a sunny spring day, the blossom is in the trees, multicoloured flowers pepper the verges as you walk down the path. The wind picks the blossom and blows it past your face in a cloud, an unfragranced cloud. Stooping down, you press your face to a flower, and inhale deeply, finding it completely odourless. Frowning, you try another and another, not a smell among the bunch.

Suddenly a sopping wet cat runs past, followed by a dog sporting the 'drowned rat' look. The dog bowls you over; as you cry out, it turns, and breathes hotly into your face, its breath heat only; the smell of wet dog completely non-existent. As the dog disappears, you brush yourself off, and continue down the path.

A picnic area opens out, people eating on the grass. No scents of hot food assaults you; picking up an apple you bite down. Juice flows into your mouth, but that is all, you taste what's on your tongue, but it might as well be soggy cardboard.

Smell is a sense often overlooked in a virtual world. Developers discount its importance, as a minor sense, when in truth we rely on it as an input channel to flesh out the world around us.

Scents carry on the breeze, and they are with us all the time: from the perfumed odours of pollen blowing in the wind, to the pong as you pass a full dustbin, to the aroma of freshly cooked food wafting out of a pub. In fact, taste functions poorly without smell.

Around seventy-five percent of the perceived taste of a food is actually sense of smell. Taste buds only allow us to perceive bitter, salty, sweet, and sour flavours. It's the odour molecules drifting up to the nose from food that give us most taste. Without that, we can only make out the above - near tasteless food.

Localisation by Smell

Of all our senses, smell is our most primal. Animals need the sense of smell to survive. Although a blind rat might survive, a rat without its sense of smell can't mate or find food. Smell can also be used to navigate: you cannot see that meat bog beyond the forest yet, but you can certainly smell it.

Smell cannot tell us too well a direction, only that something stinky is nearby. We rely on other senses to find out where, smell just warns us that it is nearby, when the source may be out of sight and beyond hearing. Removing the smell from the equation takes away one of our senses, abstracts the realism of the environment.

How often have you identified someone by their perfume or after shave? Been tempted to buy some food based only on the wonderful smell wafting out? Breathed deeply in as you open a new jar of coffee? Held your nose as you've walked past a dung heap?

Not all smells are pleasant, but all help us to localise.

Smell can easily be as much a part of an object as it's shape.

Training by Smell

Our sense of smell operates at the barely-conscious level, and is proven to be intimately tied to memory. A familiar smell almost instantly brings recollection of the last time you smelt it. Thus, smell is a wonderful tool for training.

Picture the advantages of training future surgeons on a virtual patient, and they accidentally puncture the liver. Immediately, the simulator produces the appropriate smell, training them to identify a punctured organ, long before they see the damage, if they otherwise would at all.

Mechanical training and aerospace works so muvch better when as well as teaching how to weld, or solder, or examine a fault by visual inspection, you can add in the scent of burnt wiring, or scorched plastic, and teach people to be guided by their nose to damaged areas - without the costs involved in damaging an actual plane.

For childhood education, the possibilities are no less wondrous; a class visits India remotely, and is beset by the aroma of exotic spices flooding the classroom as they research. Lush, tropical garden smells wash over them from research about Hawaii. A geography class covering the ring of fire, has the faint odour of brimstone throughout. Even in early learning, an infant learning to read is aided by apple smells from the apple, muddy smells from the dog, facilitating swifter learning.

Healthcare

The loss of the natural sense of smell, especially in older people, can be a warning of the encroachment of degenerative diseases. Using VR based scents, which pass through the olfactory nerves instead of completely bypassing them, interactive testing is possible, to monitor the state of the olfactory pathways.

Additionally, direct-stimulation of the olfactory nerve could allow smell to be rekindled after it is lost, bringing back the pleasure of food.