Sensory Perception

Sensory Perception - Process of Sensory Perception

Introduction:

Perception:

Perception simply means the use of the senses in our possession to get a better understanding of the world. It is the process of becoming aware of something through the senses.

Sensory Perception:

An organism or individual must be capable of performing the neurophysiologic process of the stimuli in their environment for them to possess what is called a sensory perception.

This process happens to be done through the organs usually the senses like sound, hearing, vision, taste, smell, and touch. The sensory perception involves detecting the stimuli, characterizing, and recognizing it.

The process of sensory perception stimulates when something in the real world encourages the sense organs.

For instance, stimulating the eyes or warmth, light reflects off a surface, emanates from a hot cup thereby stimulating the touch senses or receptors in the skin.

The commonly known senses are represented as processes beneath sensory perception.

Some have common names like visual perception or electroception. The sensory perception of pain would come from mechanical, temperature, electrical or chemical stimuli. The senses of both smell and taste use the chemical stimuli. The senses tend to be weaker along with the age.

There are five different stimulus types involved in sensory processing, i.e. chemical, mechanical, temperature, electrical, and light.

Sensory perception has three steps:

We perceive the world through the five senses (smell, hear, touch, taste, sight)

  • 1. The human sense receptors are stimulated by sensory information.

  • 2. The brain translates the sensory information into sensations such as taste, temperature etc.

  • 3. Higher centres in the brain would recognize or ignore the sensations and their meanings.

  • Sense perception is an important dimension of comprehending the world around us. The sensory perception allows us to gather the outside information and hopefully make sense out of it.

    The things that affect the sense perception are:

  • • Motivations

  • • Emotions

  • • Biases

  • • Interests

  • • Expectations

  • • Cultural perspectives

  • • background experiences

  • Every living organism has a unique range of senses. All organisms have a different range of senses. Humans are limited to five senses. When the humans sense the world around them, they will not be able to understand the surroundings they can only comprehend the environment through the limited range of senses.

    Advances in modern science all know that radio waves, infrared radiation, and sounds at high and low frequencies’ and many more are constantly in the environment. So, the humans cannot detect any of these and perceive 100% of their surroundings. In this way, they are limited by a range of human senses.

    The sensory receptor is a cell or a group of cells that detect the stimuli. The sensory receptors can be classified based on stimuli to which they respond. 

  • • Chemoreceptors

  • • Mechanoreceptors

  • • Thermoreceptors

  • • Photoreceptors

  • • Baroreceptors

  • Chemoreceptors are those which respond to the chemical stimuli.

    Mechanoreceptors are those which respond to mechanical stress or strain. i.e. movement.

    Thermoreceptors are those which respond to temperature changes.

    Photoreceptors are those which respond to variations in light.

    Baroreceptors are those which respond to pressure.

    Sight:

    Sight or vision described the ability of the eyes and brain to detect the certain wavelengths of electromagnetic radiation i.e. light and to interpret the image as sight. Different receptors are responsible for the perception of colour and the perception of brightness. Photoreceptors are found in the retina. As shown in the figure:



    The structure of the eye owes completely to the task of focusing light on the retina-inner layer of the eye, and light sensitive. First, the light passes through the clear protective layer called the cornea. Then the light passes through the pupil which is the opening in the iris and into the interior of the eye.

    After passing through the pupil the light travels through a lens, a transparent biconvex structure, along with the cornea helps to focus on the retina. Muscles attached to the lens change the shape of the lens to bend the light rays so that they can focus on the retina. The light hitting the retina causes chemical changes in the photosensitive cells of the retina.

    The retina has two important photosensitive cells that are needed for the vision- they are rods and cones. The rod cells are highly sensitive to light, which will allow them to respond to dim light and dark but cannot detect the colour. These allow humans and animals to see by the moonlight or dim light.

    Cone cells respond to the different wavelengths of bright light to initiate the nerve impulse. They are responsible for the sharpness of the images. A cone cell does not respond well in the poor light conditions. 



    This figure shows how light is focusing on the retina. This also shows how light from the distant source is bent by the stretched lens to strike the retina. And in the second figure, it shows how light from a closer source is bent even sharply by the relaxed lens to strike the retina.

    The humans have three different types of cone cells that respond to the different wavelengths of light they are red, green, and blue. The cone cells contain the pigment that absorbs the energy from different wavelengths of light to initiate the nerve impulse.

    The brain integrates the nerve impulses from the cone cells and perceives the world in all the colours of the visual spectrum.

    Hearing:

    The Hearing is the sense of sound perception that results from the movement of tiny hair fibres in the inner ear. Sound can be detected as vibrations that are conducted through the body. Sound wave frequencies that are too low or too high to be heard by the ear can be deducted through this way. Audible sound is sensed by the ear.

    The folds of the cartilage surrounding the outer ear canal are called the pinna. Sound waves gathered by the pinna and channelled down the auditory canal that is a tube-shaped opening of the ear that ends at the tympanic membrane or the eardrum.

    Sound waves travelling through the ear canal hit the eardrum and cause it to vibrate. These vibrations travel across the air-filled middle ear cavity and through the group of three tiny bones that are delicate- the hammer, the anvil, and the stirrup.



    The group of bones that are delicate will amplify and transfers the eardrum vibration to another membrane called the oval window. The oval window splits the inner ear from the middle ear.

    The inner ear contains the cochlea. The cochlea is a coiled tube that is filled with a watery fluid that moves in response to the vibrations coming from the middle ear through the oval window. As the fluid moves around, thousands of mechanoreceptors called the hair cells to bend, releasing neurotransmitters.

    A very strong movement of the fluid within the cochlea caused by very loud noise can kill the hair cells. This is a common cause of partial hearing loss and is the reason why users of firearms or heavy machinery should wear earmuffs or earplugs.

    The destruction of hair cells usually leads to permanent hearing loss; once the hair cells are destroyed the hairs do not generally grow back.

    Balance and the ears:

    The ears are also fundamental for the sense of balance. The semi-circular canals are three fluid-filled interconnected tubes forum inside the ear. They can be seen directly above the cochlea. The canals are positioned at an angle between 95 to 115 degrees relative to one another. The angles between the canals are not perpendicular so movements of the head cause the fluid to move in two canals at the same time.

    Each canal is filled with a liquid called endolymph, and motion sensors with little hairs called cilia. The hair cells sense the strength and direction of the fluid movement and send electrical signals to the cerebellum, which interprets the information and responds to help keep the body sense of balance.

    The balance will be interrupted when there are dizziness and nausea. Balance can be upset by an inner ear infection, a sinus infection, a bad cold, or several other medical conditions. The balance can be temporarily disturbed by rapid and repetitive movements like riding, spinning around the circle etc.

    Taste and smell:

    Taste is one of the main chemical senses- and the other is the smell. There are four types of taste receptors on the tongue of humans. The human tongue has about 100 to 150 taste receptor cells. Taste stimuli from each receptor send information to a different region of the brain. The four receptors detect the sweet, salt, sour, and bitter. The existence of a fifth receptor, for a sensation, is called umami. Tomato is a major component of umami.

    The umami receptor detects the amino acid glutamate, which causes a savoury flavour in foods. The chemoreceptor of the mouth is the taste cells that are found in bundles called taste buds. Most of the taste buds are embedded within the tiny papillae that cover the tongue. The tiny papillae are otherwise called as bumps.

    Each receptor has a different way of detecting certain compounds and begins an action potential that alerts the brain. The compounds present to bind to receptors in the taste cells and stimulate the neurons in taste buds. The tongue can also feel the sensations that are not generally called tastes. These include temperature, spiciness, hotness, fattiness, and coolness.



    Smell:

    Smell is another chemical sense. The chemoreceptor of smell is called the olfactory receptors. About 40 million olfactory receptor neurons line in the nasal passage. Smell is most primal of the senses. It is also an interactive sense.

    Different odour molecules bind to and excite olfactory receptors that are specific. The combination of excitatory signals from different receptors makes up what humans identify as the smell. Olfactory receptor neurons in the nose differ from most other neurons in that they die and regenerate on the regular basis.

    A dog’s keen sense of smell is due to the large areas of its nasal passages that are covered by olfactory receptors in the nose and many nerves that bring nerve impulse from the receptors to the dog’s brain. 



    The area in which olfactory receptors are located inside the human nose also called as olfactory epithelium measures about 12 cm2 and the olfactory epithelium of some dog’s nose can measure about 15 cm2.

    The olfactory receptors and taste receptors both contribute to the flavour of food. The tongue can only tell among a few different types of taste, while the nose can distinguish between hundreds of smells even if only in tiny amounts. The combination of the tongue’s tastes, and nose smell information is used by the brain to determine the taste.

    Touch, Pressure, and Pain:

    Touch is the sense of pressure perception which is felt in the skin. There are a variety of pressure receptors that respond to variations in tension and pressure. Mechanoreceptors are most numerous on the tongue, lips, face, soles of the feet and palms.

    There are several types of pain receptors called nociceptors which would respond to potentially damaging stimuli. They are mostly found on the external parts of the body like skin, mucous membrane, cornea, also found in muscles, joints and some internal organs.

    Nociceptors are classified according to the stimuli to which they respond to mechanical, chemical, and thermal. But some of the receptors respond to many of the different damaging stimuli of a chemical, thermal or mechanical nature.

    The thermal receptors are activated by potentially harmful cold or heat. The cold temperature would range from below 5 degree Celsius or 41 degrees Fahrenheit. And heat temperature would range from above 45 degree Celsius or 113 degrees Fahrenheit.
    The mechanical receptors respond to excess pressure, bending, squeezing. These are the types of painful stimuli that a cactus would cause.



    Mechanical pain receptors in the skin would warn the human if they get too close to this prickly cactus. The nociceptors allow the organism to feel the pain in response to damaging pressure, excessive heat and cold, and a range of chemicals, the majority of which are damaging to the tissue surrounding the nociceptor.