Imagine if you encountered a being who had never seen, who was unable to smell and could not even perceive tactile stimuli, like touches or textures; and despite lacking these faculties, you were tasked with explaining to them what a field of tulips is. How would you describe the vibrant colors of the flowers and leaves without resorting to sight? How would you explain the fragrance of the tulips and the wet earth without relying on smell? And how would you talk about the soft texture of the petals without using touch? Difficult... It’s hard to explain with words something that needs to be felt to be understood. This is the beauty of the senses; they give us a peculiar understanding of the world.
Since we were little, we have learned that humans have five senses: sight, hearing, smell, taste, and touch. However, various authors show a broader classification that (despite the variations in terminology attributed by each of them) groups sight, hearing, smell, and taste into the class of special senses, as they involve quite specific sensations; while touch would be part of a set designed to provide information about the body, making up the sensory modality known as somesthesia.
Somesthesia is responsible for the sensory information of what happens throughout the body and is divided into several submodalities, among which the most important are: proprioception, which is the ability to distinguish the position of the body and its parts; thermosensitivity, which provides us with information about cold and heat; pain, which identifies potential or real stimuli that cause injuries to our tissues; and touch, responsible for the perception of things that touch our skin. The latter, in addition to being part of our daily lives, is closely related to our emotions, which is why we will return to discuss it in more detail. On the other hand, thermosensitivity and pain are essential to protect the individual from potentially harmful stimuli, so what would be the importance of proprioception?
To investigate how touch and proprioception participate in the discrimination of objects, a study evaluated how participants, who had their eyes covered, distinguished a cylinder, a bar, and a misaligned cube (diagonally) among several aligned cubes on a board. The result showed that tactile information alone was sufficient to distinguish the cylinder among the cubes; however, proprioceptive information proved essential to provide information about the height and orientation of the object, necessary to detect the bar and the cube diagonally. This shows that, although sometimes a single sensory modality is sufficient for product recognition, in general, we use more than one sense in this interaction, and in certain cases, this combination is essential.
“Something terrible has happened. I can’t feel my body. I feel strange – disembodied.” These words, reported by Christina, a patient who lost proprioceptive ability after surgery, give us an idea of the impact caused by the loss of this function. After discovering a way to cope with the situation, even though far from ideal, she explains, “So what I have to do is use my sight, use my eyes in every situation where I previously used proprioception. I’ve already noticed that I can ‘lose’ my arms. I think they are in one place and find out they are in another. Proprioception is like the eyes of the body, the way the body sees itself.”
This example, in addition to showing us the importance of proprioception, also highlights another characteristic of the senses, which is the ability to compensate for the loss of a certain function by making greater use of another that is intact or in better condition. Experience shows us many successful cases of this substitution; for example, have you ever imagined how it would be to teach classical ballet to blind dancers? How would they learn the movements and imitate them without being able to see? A teacher discovered the answer to this question by betting on the use of another sense. What would it be? We will return to this topic in the next post!
References
Hall JE. Somatic sensations: I. General organization, the sensations of touch and body position. In: Medical Physiology (Guyton, AC; Hall, JE). 2011; p. 603-614, Elsevier;
Lent R. The senses of the body. In: One Hundred Billion Neurons – Fundamental Concepts of Neuroscience (Lent, R). 2004; p. 211-39, Atheneu Publishing;
Overvliet KE, Smeets JBJ, Brenner E. The use of proprioception and tactile information in haptic search. Acta Psychologica. 2008;129(1):83-90;
Sacks OW. The disembodied woman. In: The Man Who Mistook His Wife for a Hat (Sacks, OW). 1997; p. 59-70, Companhia das Letras.
