Inside the Research · Issue 1
Perhaps we are asking the wrong question
Close your eyes and slowly bring a finger to the tip of your nose. In most cases the gesture succeeds without difficulty. We cannot see the arm, we have not yet touched the face, and no sound informs us of its trajectory. Yet we know, with sufficient precision, where the hand, elbow, and shoulder are.
Now imagine standing up suddenly from bed. For a moment we may feel unstable, as though the floor had tilted. Here too vision has not necessarily failed: the vestibular system, located in the inner ear, registers acceleration of the head and helps maintain balance, posture, and stability of gaze.
Neither limb position nor balance appears in the traditional list of five senses. Should we therefore conclude that there are seven? And where should we place pain, temperature, hunger, thirst, itch, fatigue, breathing, or heartbeat?
A More Complex Legacy Than It Seems
The list of five senses is usually traced back to Aristotle. That is broadly correct, but it risks oversimplifying his thought. Aristotle distinguished sight, hearing, smell, taste, and touch according to the objects each faculty was specifically able to perceive. He also recognized that properties such as movement, shape, and magnitude could be perceived through more than one sense. Even in the Aristotelian model, perception is not simply a juxtaposition of sealed channels.
The classification has survived for centuries because it has remarkable intuitive force. Each sense seems to correspond to a recognizable organ, a type of stimulus, a particular conscious experience, and an easily described function. But as soon as we try to turn that intuition into a scientific definition, difficulties begin.
Touch Is Not One Thing
In everyday language we say that we touch when we feel pressure, vibration, a smooth surface, a point, heat, or cold. We may also feel pain, itch, or the position of the hand. All these experiences concern the body, but they do not depend on a single type of receptor or necessarily travel along the same pathways.
Proprioception provides information about joint position, limb movement, and muscular force. Signals come from receptors in muscles, tendons, joints, and also the skin. Through their continuous updating, the nervous system constructs an operational model of the body, necessary for planning and correcting movement and for distinguishing one’s own body from the environment.
Should proprioception be considered part of touch or an independent sense? From a functional point of view the difference is substantial: cutaneous touch mainly informs us about contact with the external world, whereas proprioception concerns the body’s configuration and movement. Calling it a sixth sense may be useful as a reminder, but it does not solve the theoretical problem.
The Body Also Perceives Itself
In recent years, increasing attention has focused on interoception, broadly defined as the detection and interpretation of signals originating within the organism. Heartbeat, breathing rhythm, stomach distension, internal temperature, and many visceral processes continuously send information to the nervous system.
Presenting interoception as a single internal sense can, however, be misleading. Being able to perceive one bodily signal accurately does not necessarily imply equal accuracy for another. Performance measured through heartbeat tasks cannot simply be extended to breathing or gastric activity, and results also vary according to the experimental task used.
Research distinguishes at least the physiological signals available, attention directed toward the body, the accuracy with which some signals are recognized, beliefs about one’s own sensitivity, and the interpretation given to the sensation. Feeling the heart beat, intentionally focusing on it, and believing oneself to be highly sensitive to cardiac signals are not the same thing.
The Signal Does Not Contain Its Meaning
An increased heart rate can accompany physical effort, fear, excitement, fever, or the intake of a stimulant. The physiological signal does not carry a label specifying its cause. To understand it, the system must integrate it with context, expectations, memory, and other available cues.
This does not mean that bodily sensations are imaginary. It means that perceiving a signal and attributing meaning to it are related but distinct operations.
When Several Senses Become One Experience
Think of the flavor of a peach. In everyday language we attribute almost the whole experience to taste. In fact, the tongue detects some basic taste qualities, while a decisive part of aroma depends on volatile molecules that reach the nasal cavity from the mouth during chewing. Texture, temperature, chemesthetic sensations, color, expectations, and even some sounds produced by the food also contribute.
Taste and smell have distinct peripheral receptors, but their information is integrated in the construction of flavor. Should flavor therefore be considered an autonomous sense? If we define the senses through peripheral organs, probably not. If we use the unitary object of experience as our criterion, the answer may differ.
Five, Seven, Twenty: What Are We Counting?
If we call a sense any system equipped with a macroscopically recognizable organ, we will remain close to the traditional five, perhaps adding balance and proprioception. If we distinguish systems according to receptor types and stimuli, the number rises. If we consider functions or the quality of conscious experience, the classifications change again.
The number of senses is therefore not a hidden quantity in the body that science simply has to discover. It is also the result of a classification: it depends on which differences we consider theoretically and practically significant.
Why We Still Speak of Five Senses
The old list need not be abolished. It still describes five major ways in which humans experience the environment and retains a communicative clarity that is difficult to replace. The problem arises when a schoolroom classification is mistaken for a complete map of perception.
From List to Fabric
To the question “How many senses do we have?” we can therefore answer only with another: according to what criterion? The most interesting issue is not whether the correct number is seven, twelve, or twenty-one. It is to understand what information an organism can detect, through which receptors and circuits, which signals reach consciousness, and how they are integrated.
The senses are not independent windows, each cut into a separate portion of the world. They are specialized systems that meet, correct one another, compete, and cooperate. Counting separates. Perceiving means building relations.
Essential Reading
Greenwood, B. M.; Garfinkel, S. N. (2025), “Interoceptive Mechanisms and Emotional Processing”, Annual Review of Psychology, 76, pp. 59–86. DOI: 10.1146/annurev-psych-020924-125202.
Ritz, T. (2025), “Interoception Research 40 Years Later – Revisiting James Pennebaker’s Critique”, Biological Psychology, 199, 109069. DOI: 10.1016/j.biopsycho.2025.109069.
Engelen, T.; Solcà, M.; Tallon-Baudry, C. (2023), “Interoceptive Rhythms in the Brain”, Nature Neuroscience, 26, pp. 1670–1684. DOI: 10.1038/s41593-023-01425-1.
Macpherson, F. (ed.) (2011), The Senses: Classic and Contemporary Philosophical Perspectives, Oxford University Press.
