How Do Our Senses of Smell and Hearing Work?


By Catherine A. SandersonAmherst College

We have over a thousand different types of olfactory receptors in our nose, allowing us to detect more than 10,000 distinct smells. But, an important way that our sense of smell is more powerful than the mere number of receptors is how it plays a unique role in evoking memories and feelings. Meanwhile, the human sense of hearing, at perhaps the most basic level, can alert us to potential danger: the rattle of a snake, the roar of a train.

Plastic model of the human ear’s anatomy
The human sense of hearing is accomplished when air molecules are guided through the outer ear and vibrate the eardrum. (Image: Edwardolive/Shutterstock)

Amplitude in Decibels

The outer ear channels sound waves, produced by air molecules through the auditory canal, cause the eardrum to vibrate. These vibrations then travel to the inner ear, which generates neural signals that are sent to the brain.

Sound waves vary in length, frequency, height, and amplitude. More frequent, or shorter, waves have a higher pitch, like the keys on the far right end of a piano. Longer waves have a lower pitch. Amplitude, or loudness of sound, is measured in terms of decibels.

The absolute threshold for hearing is 0 decibels, with every 10 decibels corresponding to a tenfold increase in sound. A whisper is about 25 decibels, a normal conversation is about 60 decibels, and a subway or train is about 100 decibels.

Tone Is Important

We also form fast impressions of people based merely on the tone of their voice. People consistently perceive men with low-pitched voices as stronger and more physically attractive. Some research also suggests that lower voices in men correspond with higher levels of testosterone, suggesting that lower voices could also be a sign of increased dominance and aggression. 

These traits historically have been evolutionarily adaptive, leading to such preferences even today. Another explanation is that lower voices appear older, which could be a sign of experience and wisdom.

In one study, political scientists recorded both male and female voices saying the sentence, “I urge you to vote for me this November,” and then digitally altered the pitch of the recordings, creating a range from a low baritone to a high soprano. Four hundred people then listened to either the male or the female voices and consistently rated the deeper voices of both male and female speakers as more electable.

This article comes directly from content in the video series Introduction to PsychologyWatch it now, on Wondrium.

Sensory Interaction Between Smell and Taste

Sick woman using tissue while sitting on a couch
The close proximity of the receptors of smell and taste is the reason why people lose their ability to taste when they catch a cold. (Image: Photoroyalty/Shutterstock)

The two senses—smell and taste—are described as chemical senses, as they both rely on specialized chemo-receptor cells, meaning they process chemical stimuli—odors in the air, tastes in the mouth—and relay that information on to the nervous system. Smell and taste receptors are located near each other and interact closely. This is why you often can’t taste food well when your sense of smell is reduced by having a cold. 

Sensory interaction is also why cold pizza tastes different than hot pizza. The taste and smell sensations combine with other sensory cells that process touch and temperature, which is one reason why cold, hard pizza has a decidedly different taste than hot, soft pizza.

The part of the brain that processes smell is closely linked to parts that process memory and emotion. This is why particular odors can often trigger memories; just smelling a particular odor can take you immediately back to your grandmother’s kitchen or your high school prom.

How Pheromones Work

One of the most complex, and hotly debated, topics regarding smell is the role of pheromones, chemical signals that trigger certain responses in other members of the same species. In one particularly remarkable study of pheromones published in the journal, Nature Genetics, researchers found that women prefer men whose odor is genetically somewhat similar to their own, but not too similar.

Illustration of the olfactory system with flowers in front of a human nose
Women’s own genes influence the odor that they would prefer. (Image: Design_Cells/Shutterstock)

The researchers asked men to wear the exact same plain white T-shirt for two days and avoid anything that created a distracting odor, such as spicy foods, pets, or even deodorants. These T-shirts were then placed in boxes, where the shirts could be smelled but not seen. Researchers then asked women to smell the different boxes and pick which box they thought smelled the best. 

The women were not aware that they were smelling a shirt, or even a human odor and many said the scent reminded them of “Kmart”, presumably due to the smell of the box. So, what did they find? First, women absolutely could distinguish between the smells of different men, and overall rated the odor as “very mildly pleasant”. 

More importantly, women’s own genes influenced which odor they preferred. Women preferred the smell of shirts worn by men with somewhat similar genes to their own, but not too similar. Why? The researchers believe that preference reflects an evolutionary advantage to prefer people who are like ourselves, but not too similar, as preferring very close relatives leads to inbreeding.

Common Questions about the Human Senses of Smell and Hearing

Q: What are the two advantages of hearing in humans?

On its most basic level, the human sense of hearing can alert us to dangers lurking in close proximity. Our hearing system also lets us form an impression of somebody just by the tone of their voice.

Q: Why can’t we usually taste food when we have a cold?

The human senses of smell and taste are closely linked. Their receptors are in close proximity and react to each other. So when a cold leads to one’s sense of smell being reduced, it also reduces one’s sense of taste.

Q: Why do odors often trigger memories?

Different scents might trigger memories because the part of our brain that deals with the process of smell is in close proximity to the part that processes memories. So triggering the human sense of smell can take somebody back to an old memory.

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