Does Losing One Sense Heighten the Others?

The old, classic French architecture with the intricate balconies, the array of colorful pastries in the local pâtisserie (pastry shop) and boulangeries (bakery), and the breathtaking views of the Eiffel tower all encompass the city of Paris. Living in such a bustling and scenic city for the summer, I am fortunate enough to use all five of my senses to experience and embrace the French culture. Our vision allows us to experience colors, shapes, sizes, and more. While exploring  Paris, I was surprised to see quite a few blind people using the metro. I wondered how they learned to navigate their way around the Parisian metro system and life itself in such a visually stimulating city.

A common architectural style I’ve seen throughout

Some say that because blind people have lost their sense of vision, their other senses are heightened. Is this really true? Well to first understand how they use their other senses; we first have to understand what causes blindness. Blindness can be the cause of damage in various parts of the visual pathway, starting from the eye and ending at the visual cortex in the back of the brain within an area called the occipital lobe.

Audition, or the ability to hear and listen, helps us communicate with another, but also enjoy sounds like music. The rush of the metro coming and leaving, the bouts of sound signaling the doors to close, and the screeching against the tracks when it’s moving all encompass the experience of riding on the Paris metro system. One study looked at whether early blind adults have a better ability to detect pitch, a characteristic of the auditory cortex in the temporal lobe of the brain. 15 blind participants and 15 controls participated and were asked to discriminate thresholds of speech and non-speech stimuli (musical instruments and tones). The results show that the blind participants were able to discriminate thresholds better than thresholds. Interestingly, within the normal controls, the older the participants, their threshold of detection increased. However, the same effect didn’t occur in those who were blind, meaning that their threshold of detection didn’t increase as one would expect with age. (Arnaud et al 2018)

Now let’s switch senses and examine gustation or taste. Everyone I’ve seen in France has a unique love and great attachment to food. The four, five-hour meals, the array of pastries, and the complexity into their simple dishes constitute the Parisian dining experience. One particular study found that during gustation, congenitally blind participants showed weaker activation in the primary taste cortex compared to controls. The researchers also found that in the blind, the occipital cortex, the main area to process vision, was not used during taste processing, a contrast to controls. The researchers hypothesize that this is because blind people are underexposed to a large variety of tastes, explaining their lower activation. (Gagnon et al 2015)

The classic lineup of pastries in a pâtisserie in Paris.

What about olfaction? The smell of freshly baked baguettes is a classic staple when one walks into the boulangeries of Paris. The process of olfaction, or the sense of smell, starts with the molecules in a smell activating odor receptors in the nose. This connects to neurons in a part of your brain called the olfactory bulb and up to the olfactory cortex, where the smells are registered and processed into your memory. This was explored in a study where they showed that the blind showed better results in odor discrimination and odor threshold tasks than their control counterparts. However, both groups had shown no difference in identifying the odors. An additional aspect of this study they looked at was whether there was a difference in identifying smells in between congenital and acquired blind subjects. The results showed that there was no difference in the data between the two groups. (Comoglu et al 2015)

The areas of the brain involved in perceiving our senses.

The final sense that we will examine is touch. Sensory receptors detect and send back information to the brain, specifically to an area called the primary somatosensory cortex. Was the perception of touch enhanced in those that were blind? A group of researchers investigated whether visual judgments made by touch differed in those who were blind compared to controls. All of the participants rated different materials by touching and identifying them. In this study, the researchers found that there was no difference between those who were blind and controls in terms of identifying or categorizing them. (Baumgartner et al 2015)

The 70 different materials or touch stimuli that the participants had to identify

Now that we explored all the senses, we can come to a conclusion that although blind people have adapted with using their other senses, only some senses have proved in specific studies to be heightened in those individuals. Taste, smell, and audition are shown to have better discriminatory thresholds versus normal participants, but touch does not show any difference between the blind and normal participants. However, we must keep in mind that blind people also seem to compensate with their other senses, which a lot of researchers have addressed as the reason for their “heightened” perception. All of our senses deserve importance and personally, my time in Paris has made me appreciate every new experience that I come across.

Bibliography

Arnaud L, Gracco V, Ménard L. Enhanced perception of pitch changes in speech and music in early blind adults.Neuropsychologia. 2018 Aug;117:261-270. doi: 10.1016/j.neuropsychologia.2018.06.009.

Gagnon L, Kupers R, Ptito M. Neural correlates of taste perception in congenital blindness. Neuropsychologia. 2015 Apr;70:227-34. doi: 10.1016/j.neuropsychologia.2015.02.027.

Çomoğlu Ş, Orhan KS, Kocaman SÜ, Çelik M, Keleş N, Değer K. Olfactory Function Assessment of Blind Subjects Using the Sniffin’ Sticks Test. Otolaryngol Head Neck Surg. 2015 Aug;153(2):286-90. doi: 10.1177/0194599815583975.

Baumgartner E, Wiebel CB, Gegenfurtner KR. A comparison of haptic material perception in blind and sighted individuals.Vision Res. 2015 Oct;115(Pt B):238-45. doi: 10.1016/j.visres.2015.02.006.

First two photos taken by myself

Image of brain- http://www.d.umn.edu/~jfitzake/Lectures/DMED/SensoryPhysiology/GeneralPrinciples/Figures/SensoryCortex.jpg

Image of materials from Baumgartner et al 2015

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