Following note contains detailed note on, ‘Physiology & Perception of Senses- Vision, Audition, Chemical & Somatosensory.’
Contents
Physiology & Perception of Vision
- What is light? Albert Einstein who first proposed that light is actually tiny “packets” of waves. These “wave packets” are called photons and have specific wavelengths associated with them (Lehnert, 2007; van der Merwe & Garuccio, 1994)
- Its psychological properties, there are three aspects to our perception of light:
- Brightness– how strong or weak light appears, determined by the wave’s height. Higher waves are brighter, and lower waves are dimmer
- Color– It comes from the wave’s length: longer waves are red, and shorter waves are blue
- Saturation– purity of a color. A pure red has only red waves. Mixing colors, like adding white, makes it less pure and changes its shade, like pink.
Physiology of Vision (Ophthalmology)
- Eye Structures: The eye consists of the cornea, lens, retina, and optic nerve.
- Light Reception: Light enters the eye through the cornea and lens, which focus it onto the retina.
- Retinal Processing: Photoreceptor cells (rods and cones) in the retina convert light into electrical signals.
- Neural Pathway: Electrical signals travel via the optic nerve to the visual cortex in the brain for processing and interpretation.
Perception of Vision:
- Gestalt Principles: Our brains organize visual information into meaningful patterns using principles like proximity, similarity, closure, and continuity.
- Depth Perception: The ability to perceive the relative distance of objects in three-dimensional space is achieved through binocular cues (e.g., retinal disparity) and monocular cues (e.g., relative size, interposition).
- Trichromatic Theory: by Thomas Young & Helmholtz, suggests that color vision is based on the combined activity of these three types of cones. Three types of cones: those sensitive to short (blue cone), medium (green cone), and long (red cone) wavelengths of light.
- Opponent Process Theory: Ewald Hering suggests that color perception is based on opposing neural mechanisms, such as red-green and blue-yellow. For example, If a person stares at a picture of the Indian flag for a little while and then looks away to a blank white wall or sheet of paper, that person will see an afterimage of the flag. Afterimages occur when a visual sensation persists for a brief time even after the original stimulus is removed.
- Color Constancy: It refers to the ability to perceive the color of an object consistently under varying lighting conditions. This phenomenon is thought to involve both physiological mechanisms in the visual system and cognitive processes that help us interpret the true color of objects despite changes in illumination.
Physiology & Perception of Audition
Physiology of Audio:
Ear Structures: The ear is divided into the outer, middle, and inner ear.
- The outer ear includes the pinna (the visible part of the ear) and the ear canal. The pinna helps collect sound waves and direct them into the ear canal. The ear canal, also known as the auditory canal, is a tube-like structure that carries sound waves to the eardrum.
- The middle ear begins at the eardrum (tympanic membrane), which separates it from the outer ear. Behind the eardrum are three small bones called the ossicles: the malleus (hammer), incus (anvil), and stapes (stirrup). The ossicles transmit and amplify sound vibrations from the eardrum to the inner ear. The middle ear is also connected to the back of the throat by the Eustachian tube, which helps equalize air pressure between the middle ear and the environment.
- The inner ear contains the cochlea, semicircular canals, and vestibule. The cochlea is a snail-shaped structure filled with fluid and contains tiny hair cells that convert sound vibrations into electrical signals. The semicircular canals and vestibule are involved in balance and spatial orientation, helping maintain equilibrium.
Sound Reception: Sound waves are captured by the outer ear and funneled through the ear canal to the eardrum.
Mechanical Transduction: The eardrum vibrates, causing the middle ear ossicles (malleus, incus, stapes) to amplify and transmit the vibrations to the cochlea in the inner ear.
Cochlear Processing: Hair cells in the cochlea convert mechanical vibrations into electrical signals.
Neural Pathway: Electrical signals travel via the auditory nerve to the auditory cortex in the brain for processing.
Perception of Audio:
Auditory Scene Analysis: Our brains can separate and organize different sound sources in complex auditory environments.
Pitch and Timbre Perception: Pitch is perceived based on the frequency of sound waves, while timbre refers to the quality or tone color of a sound. Sound has psychological properties-
- Frequency or pitch- shorter wavelengths = more waves per second = higher frequencies. Theories of pitch (Place theory, Frequency theory, volley theory)
- Volume – larger wave amplitudes associated with louder volume
- Timbre – increase in number of sounds results in greater richness
Sound Localization: The brain uses auditory cues (e.g., differences in timing and intensity between ears) to determine the location of sound sources.
Physiology & Perception of Smell (Olfaction)
Physiology of Sensory & Perceptual Processes Chemical (Olfaction). The sense of smell is a chemical sense.
Physiology of Smell (Olfaction)
Nose Structures: The nose contains olfactory receptors. The outer part of the nose serves the same purpose for odors that the pinna and ear canal serve for sounds: Both are merely ways to collect the sensory information and get it to the part of the body that will translate it into neural signals.
Olfactory Receptor : these are chemical receptors. Odor molecules bind to olfactory receptors, triggering electrical signals.
Neural Pathway: Signals travel via the olfactory nerve to the olfactory bulb and then to the olfactory cortex for processing.
The olfactory bulb is a structure located at the base of the brain that acts as the first processing center for olfactory information.
Perception of Smell:
Odor Discrimination: Our brains can distinguish between thousands of different odors and tastes based on the activation patterns of olfactory and gustatory receptors.
Hedonic Perception: Odors and tastes can evoke emotional and hedonic responses, influencing our preferences and aversions.
Genetics:determining the types and numbers of olfactory receptors we possess. This can influence our sensitivity to certain smells.
Past Experiences:Our past experiences with smells can shape how we perceive them in the present. The smell of freshly baked cookies might remind you of happy childhood memories, making the scent more pleasant.
Concentration:The concentration of odor molecules in the air can affect how strong a smell we perceive. Higher concentrations lead to more intense odor experiences.
Other Sensory Cues:The perception of smell is often intertwined with other senses, particularly taste. This is why food often tastes different when you have a cold and your sense of smell is diminished.
Physiology & Perception of Taste (Gustation)
Hans Henning (1917) proposed that there are four primary tastes: sweet, sour, salty, and bitter. Lindemann proposed that this fifth taste be called ‘umami’ i.e. glutamate—adds a pleasant flavor to foods.
Physiology of Taste (Gustation)
Taste Buds: Taste buds on the tongue contain taste receptor cells.
Chemical Reception: Taste molecules bind to taste receptors, initiating electrical signals.
Neural Pathway: Signals travel via various cranial nerves to the gustatory cortex in the brain for processing.
Perception of Taste:
- Flavor Perception: Flavor is a multimodal experience that combines taste, smell, texture, and temperature sensations.
- Smell:Our sense of smell plays a significant role in taste perception. Volatile odor molecules travel from the back of the mouth to the olfactory receptors in the nose, contributing to the overall flavor we experience. This is why food often tastes bland when we have a stuffy nose.
- Trigeminal nerve:This cranial nerve is responsible for detecting sensations like texture, temperature, and pain in the mouth. The trigeminal nerve also contributes to the perception of flavor by detecting pungency, spiciness, and coolness.
- Learning and experience:Our preferences and experiences can shape our taste perception. For instance, exposure to certain flavors early in life can influence our liking for them later.
Physiology & Perception of Touch (Somatosensory)
Physiology of Touch (Somatosensory):
Skin Receptors: The skin contains various receptors for touch, pressure, temperature, and pain.
Mechanical and Thermal Transduction: Receptors convert mechanical and thermal stimuli into electrical signals.
Neural Pathway: Signals travel via sensory nerves (e.g., dorsal root ganglia) to the somatosensory cortex in the brain for processing and perception.
Perception Of Touch
Tactile Sensation: Our brains interpret tactile sensations (e.g., touch, pressure, vibration) based on the activation of various skin receptors.
Pain Perception: Pain is a complex perceptual experience influenced by physical, emotional, and cognitive factors.
Proprioception and Kinesthesia: Our brains use proprioceptive and kinesthetic information to perceive the position, movement, and orientation of our body parts
References:
Conway, B. R. (2020). Color Vision, Cone Opsins, and Color Discrimination. In K. A. Sharpe & A. Nordby (Eds.), The Oxford Handbook of the Science of Perception (pp. 247-268). Oxford University Press.
Hurlbert, A. C., & Wolf, K. (2021). Color Vision. Current Biology, 31(5), R216-R220.
Kingdom, F. A. A. (2021). Color Vision. Annual Review of Vision Science, 7, 331-357.
Witzel, C., & Gegenfurtner, K. R. (2018). Categorical sensitivity to color differences. Journal of Vision, 18(12), 8.