Perceived information can be divided into groups; correspondingly, the receptors that respond to these stimuli:
- Mechanoreceptors respond to mechanical stimuli, i.e., pressure, touch, stretch, or vibration. They mediate tactile perception (sense of touch) and, together with the sense of balance in the inner ear, proprioception, i.e., the position and movement of the limbs in space (sense of posture and strength). The baroreceptors in the body measuring blood pressure and the hairs of the auditory cells in the inner ear (which respond to their bending as a result of sound waves) also belong to the mechanoreceptors.
- Thermoreceptors detect temperature differences, and there are special sensors for both cold and heat.
- Chemoreceptors measure the concentration of dissolved substances in body fluids. Well-known representatives of this group are the taste or odor receptors, others play an important role in the regulation of respiration (by measuring the oxygen or carbon dioxide distribution) or – as osmoreceptors – in hormone, water and salt balance.
- Photoreceptors respond to light – most important are the rods and cones in the retina, which mediate vision.
- Pain receptors are found almost everywhere in the body and respond quite unspecifically to various stimuli such as heat, strong mechanical impact on body tissues (for example, bruising) or toxic chemical substances. They mediate the sensation of pain (nociception).
In the center – processing in the brain
Once the signals are received, they are transmitted via associated neural pathways to the appropriate sensory centers in the brain. This initially functions as a filter to direct the maelstrom of incoming information into meaningful channels: only a few sensory impressions pass through this sieve and are processed further. If you imagine how many blades of grass move in the wind on a meadow where you only notice the colorful butterfly, it becomes clear how important this selection is.
Perception occurs regardless of the viewing angle, the weather, the shape and color of the butterfly, or whether we are 20 centimeters or 20 meters away – this makes it clear what a complex achievement lies behind even these first steps. The remaining stimuli have to be processed and interpreted.
Our brain also draws on memory in this process – have I ever seen such a rocking fluttering thing before? Is it a pair of pants on a line, a balloon at a fair, a child on a wooden board?
An image of the environment is created
Until the butterfly is recognized as such (and perhaps even determined to be a peacock butterfly), the brain again has to work quite hard. To do this, the stimuli arriving from the various sensory organs are coordinated and combined into an overall view:
- Is the butterfly far away or can I hash for him?
- Is it big or small, red or yellow?
- Does it smell like something, does it make noise when flapping its wings?
Perhaps you also feel a pleasant feeling at the sight of him, because he evokes memories of trips together with grandpa.
So what ultimately emerges is an image of the environment, but one that shows only a small section and is subjectively shaped. For this, the work of the brain depends not only on the experiences, but also on the state of the organism (for example, hunger, fatigue, mood).