There are many processes involved in the perception. These sequences ofsteps are called perceptual processes. These are, environmental sitimulus, attended stimulus, the stimulus on the receptors, transduction, neural processing, perception, recognition and action.

The main principle of perception is based on electrical signals that are created in the receptors in our nervous system. Transduction is the transformation of one form of energy into another form of energy. After transforming energy into electrical signals, neurons are activated. These signals are transmitted to the brain. Transmission to the brain is crucial for perception. During this transmission, neurons interact with each other. This electirical energy is proccessed through networks of neurons, which is called neural processing.

Sensation refers to the process of sensing our environment through touch, taste, sight, sound, and smell. Sensation includes the information contained in the enviromental stimuli that are captured by the relevant sensory system and transmitted to the brain.

Perception is the process of analyzing, recognizing, interpreting, and organizing the incoming information.

Absolute threshold is explained as the energy level at which the lowest level stimulus is noticed or discerned by the human senses, including vision, hearing, taste, smell and touch.

The light, which is a form of electromagnetic energy, affects the photoreceptors of the retina. This triggers processes that produce neural signals and then progresses through the neural networks. The lateral geniculate nuclei (LGN) in the thalamus and the signals from the cerebral cortex mediate different visual functions, such as movement, shape, color, and other distinctive features of the visual world.

The two-dimensional image in the retina is perceived as three-dimensional with the deductions about depth or cues about distance. This is done by only one-eye (monocular) and two-eye (binocular) depth cues. Distance perception is the act of knowing or recognizing of a distance by previous experiences or recollective thought. Depth and distance perception refers to the ability to recognize objects by positioning them in variable distances in a three-dimensional world.

Perceptual organization involves the grouping of elements in an image to create larger objects. In the early 1900s, a group of psychologists called themselves Gestalt psychologists. They proposed the idea that the whole differs from the sum of its parts. Gesltalt psychologists argue that if the relationships between the objects around us are uncertain, the simplest and the most consistent arrangements are made to provide a perceptual organization. The important perceptual organization laws are law of similarity, law of good continuation, and law of proximity.

There are two definitions of sound: physical and perceptual. The physicaldefinition of sound refers to the pressure change in the air, whereas the perceptual definition refers to the experience that we have during hearing.

Human ear consists of three parts : inner, outer and middle ear.

The outer ear is transmits the sound waves inward sound wave reaches the eardrum through an ear canal. When the sound waves reach the eardrum (tympanic membrane), it causes vibration. As a result of this, the vibrations coming to the center are transmitted to the middle ear. The middle ear contains three bones: anvil, stirrup and hammer. The sound wave arriving at the inner ear reaches the structure cochlea, which resembles a snail shell. The fluid in the cochlea vibrates because of sound waves. There is also a section inside the cochlea that contains the hearing neurons called the hair cell. These neural signals are then transmitted to the hearing center and hearing-related areas in the brain.

The auditory system uses both monaural (one-eared) and binaural (two-eared) cues to localize sound. Each ear interacts with the incoming sound waves differently depending on the sound source. For example, the sound from the left side reaches the left ear right before it reaches the right ear. The source of voice is determined by comparing the time of arrival between the two ears and the intensity of the voice. When the voice is in a low pitch, the time to reach the ear provides more meaningful information. However, when the voice has a high pitch, the intensity provides more valid and meaningful information.

The frequency of the wave that forms the sound determines the pitch of the sound. The high frequency sound wave are perceived as high pitch; the low frequency sound wave is perceived as low pitch.

The pitch of the sound is important because it plays an important role in distinguishing people’s voices and their emotions during speech.

In humans, the sense of smell plays a role in behaviors such as finding nutrition and orienting themselves in the environment. It has also a role on social relations.

Losing the ability to smell is called anosmia. People who suffer from anosmia show us the importance of smell since these people also lose their ability to taste many foods.The reason for that is the close connection between smell and flavor.

In general, the taste sensation has the following categories: sweetness, sourness, saltiness and bitterness. Recently, a category of taste called umami has been mentioned. Umami is perceived when we taste some salts. These salts are known as monosodium glutamate and are mostly used in ready-made soups and packaged foods.

The surface of the tongue contains many ridges and valleys caused by the presence of the structures called papillae. All of the papillae (except the filiform papillae) contain taste buds and the whole tongue contains about 10,000 taste buds. When a bud is examined in detail, it is observed that between 40 and 100 taste cells are present. The signals formed in the receptors are sent to the brain stem and then to the cerebral cortex via the taste signal. The taste of the thing that the person eats is determined by the arrival of these signals at the brain.

The skin prevents dangerous stimuli from entering the body.

Humans are sensitive to mostly four tactile sensations: pressure (touch), pain, warmth and cold. These sensations are conveyed thorough receptors on the skin and in our internal organs. The skin receptor cells have an unequal distribution on the skin.

There are various types of receptors on the surface of the skin. These skin receptors respond to environmental stimuli. The receptor cells first send the signals to the medulla and thalamus; then these signals are sent to the somatosensory cortex to form a perceived sense of touch.