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The smell of freshly baked bread, a mown lawn, or gasoline evoke strong feelings and memories. Research on the relationship between smell and memory indicates that people hold a much stronger memory for aromas than they do for any other senses, including sight or sound. In “The Nose, an Emotional Time Machine,” the author, Nathalie Angier, includes work that shows people associate a smell with a memory of the very first time they smelled it, which contrasts with sight. People tend to remember the more recent times they have seen something over times further back (New York Times). In fact, experiments in Sweden showed that people over the age of seventy-five associated pictures with memories from adolescence onward but smells evoked memories from early childhood below the age of ten. Smell serves more than just a trip down memory lane. It serves as a powerful source of protection. Smell helps us detect bad food, toxic chemicals, and fire. Using sweat collected from novice sky divers before and after their first tandem jump, research by Dr. Lilianne Mujica-Parodi and others detailed in the PLOS article titled, “Chemosensory Cues to Conspecific Emotional Stress Activate Amygdala in Humans,” that people exhibit the same facial features of fear just by smelling the sweat collected from others in a fearful situation. Moreover, recent studies showed that females more than males can detect fear and disgust in men through smell alone. The research suggests that people can alert others to danger through scent alone.
In contrast to sight and hearing that detect energy in the form of light and sound waves, smell works when chemicals in the air touch special nerves in the nose. Chemical detection also goes by the name chemosensing. In the back of our nose sit specialized cells called olfactory nerves. These nerves have many tiny structures on their surface that can recognize different types of molecules floating through the air, and the nerves send a signal to the brain that describes the scent. The human nose has about six million olfactory receptors. Dogs, on the other hand, have over 300 million olfactory receptors, which explains why our canine friends can follow the scent of a fugitive that people cannot detect. Olfactory nerves, unlike nerves for sight and sound, connect directly to the part of the brain associated with memory and emotion called the limbic system, which explains the potent connections between smell, memory, and emotion.
If chemosensing, or smell, serves such a crucial element in human and animal survival and communication, it stands that computers and eventually robots would also be much better off if they could learn to smell. Significant advances in computer vision and hearing in the form of facial and object recognition and language processing already apply today in our smartphones, cameras, and computers, but scent detection remains a more distant goal. Unlike sight or sound, which records energy in the form of photons in light and waves for sound, chemosensors must not only detect tiny chemicals but differentiate between millions of different kinds of chemicals. Science has developed machines that can detect and identify different compounds. One type of chemosensing machine known as a mass spectrometer uses a combination of magnets, ions, and very sensitive electronics to identify different chemicals accurately. However, unlike the tiny cameras and microphones in our smartphones and computers, mass spectrometers usually take up part of a laboratory, weigh hundreds of pounds, and cost hundreds of thousands to millions of dollars, making them impractical for incorporation in a smartphone or robot. Like other areas of electronics though, groups continue efforts shrink both the size and cost of mass spectrometers. A research group in Indiana detailed in “Mini 11 - World's Smallest Mass Spectrometer Sniffs Out Bioterrorism and Explosives” has made a shoebox sized mass spectrometer that only weighs nine pounds. Their mass spectrometer will give sensing capabilities to military and law enforcement the unprecedented ability to detect chemicals associated with bombs and biological weapons in the field, but the size still precludes it from becoming a standard feature on your smartphone of tablet. Another chemosensing machine called a gas chromatograph separates chemicals based on the speed they pass through a long tube. Like the mass spectrometer, the gas chromatograph often takes up space and additionally needs tanks of specialty gases such as helium or nitrogen making, it impractical for a robot or smartphone. However, a company called Vernier now offers a mini-gas chromatograph that uses air not specialty gas and measures only seven and a half inches long,
Our sense of smell functions as a critical way we interact with the world and each other. It serves as a powerful connection to memory and emotion as well as protecting us from toxic chemicals and communicating danger amongst ourselves. Unlike sight and hearing that detect light and sound energy, our noses must come in contact with chemicals in the air and differentiate between the millions of different chemicals in our world. The benefits of chemosensing would extend to computers and artificial intelligence. Scientists have developed some technologies to identify different chemicals, but the machines remain too large and expensive for use in consumer technology like the smartphone or companion robot. Technology keeps shrinking chemosensors, but a mass spectrometer that fits in a smartwatch appears a far way off. So, we must wait for the time when before meeting someone we can ask, “Siri, how’s my breath?”
Dr. Smith’s career in scientific and information research spans the areas of bioinformatics, artificial intelligence, toxicology, and chemistry. He has published a number of peer-reviewed scientific papers. He has worked over the past seventeen years developing advanced analytics, machine learning, and knowledge management tools to enable research and support high level decision making. Tim completed his Ph.D. in Toxicology at Cornell University and a Bachelor of Science in chemistry from the University of Washington.
You can buy his book on Amazon in paperbackhere and in kindle format here.