Sense — The senses are the input sensors and systems by which humans (and most, if not all, animals) sense all aspects of the world around them, as well as the supporting organism's internal states. Traditionally there were thought to be five senses: sight, hearing, touch, smell, and taste, but these have been expanded over the years.

There are also some classification issues in the new list of senses, that is to say, that there are many senses which comprises multiple senses, while there are other senses that are —to varying degrees— dependent on higher level processing. In this entry, I'll try to have a top-level organization philosophy of raw vs. processed (what programmers would call "cooked").

That said, even the raw ones are often, at least slightly, processing-dependent. For example the image receptor —the retina— is comprised of multiple layers of neurons, which perform a great deal of processing within the retina itself. These early neural processing tasks include functions such as center-surround, and motion-detection.

Many sensory receptors (including the eye) also depend on efferent feedback from the brain, often out to very peripheral levels, in order to aid in clarifying a higher-level perception of what is being seen. Within these two broad (and perhaps not so well defined) classifications I'll primarily concentrate on getting them all listed, but also begin to organize things like groupings and whether they are heavily dependent on (much?) higher-level processing.

Sensory receptors are also divided by internal or external. Internal senses include states of internal body systems. Many are subconscious or autonomous, such as blood sugar and oxygen levels, and blood pressure, but there are also conscious sensations in this category, such as stomach and bladder fullness. There is also a continuum between conscious and unconscious sensations, for example, satiety.

In summary, the senses are comprised of the brain's low-level receptors (sensors) and provide a means of experiencing the world outside of the brain. Most senses, even at the peripheral (i.e., raw) level, incorporate efferent information from higher-processing center in the brain. These can be thought of, in a very abstract way, as a kind of output/effector signal that modifies how the the sensor processes stimuli, in order to provide more effective afferent sensory information.

Raw/Low-Level/Simple

• Vision — Sight. The Eye. Vision sensor field for brightness and colors in the visible spectrum
• Sound — Hearing. The ear. Hearing of (of sounds, i.e., air pressure waves) in audible frequencies
• Scent — Smell. The nose. Detection of chemical compounds in the air.
• Flavor — Taste. Sensor for detection of chemical compounds in solids and liquids placed in mouth.
• Acceleration — Balance/orientation/motion. Vestibular acceleration sensors include head-position relative to gravity. Crista within semicircular canals in inner ear.
• Haptics — Touch. A variety of raw sensory data that is provided by the epidermal receptors
  • Tactile/touch
  • Pressure
  • Thermal hot and cold
  • Wind/Breeze/Fluid- and Air-movement
  • Damage degrees leading to it. Sub-sense of the pain perception, so called pain receptors.
• Proprioception (position of limbs in space)
  • Muscle/Tendon...
    • Contraction/Displacement Position. How much muscle is extended or contracted. May be compound (processed)
    • Tension Force. How much force or effort is being applied by the muscle to the external entity.
    • Speed Velocity of contraction or extension
    • Damage and degrees leading to it. Sub-sense of pain perception, so called pain receptors.
  
  

Compound/Complex/Perception

• Somatic Sensory or Somatosensory System (proprioception and exteroception)
• Kinesthesia
  

Perceptual


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Sources and Resources

• The Vestibular System and Our Sense of Equilibrium