Psych M.D.-Sensation


Term: Sensation
Definition (Myers): The Process by which our sensory receptiors and nervous system receive and represent stimulus energies from our environment [1]
Definition (alternative): The words sensation and perception sound similar. But, they show very fine differences. Sensation is feeling something by our senses or mind. Perception is also a process or act of recognizing something through mind or senses. Though both the words sensation and perception mean sensing or perceiving something, sensation emphasizes the use of sensory organs and perception emphasizes the use of mind and intuition than the sensory organs.

Sensation is a faculty to perceive or a perception relating to stimulation of any sense organ. Perception could be sensation from sensory processes in the presence of a stimulus.[2]
Contextual explanation:
To represent the world in our head, we must detect physical energy from the environment and encode it as neural signals. This process is called sensation. Out of these encoding (sensations) we must, select, organize and interpret and make it to perception.
Sensing the World: Some Basic Principles
Psychophysics is the study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them. There are four types of stimulus.
1.Absolute Threshold is the minimum stimulation needed to detect a particular stimulus, such as light, sound, pressure etc.) 50% of the time.
2.Signal Detection predicts when we will detect weak signals, measured as our ratio of hits to false alarm. Example of a signal detection is when you can’t sleep at night, and the smallest sounds are bothering you (You can hear all sorts of sounds).
3.Subliminal Threshold is below one’s absolute threshold for conscious awareness. Basically, we can sense things unconsciously. For example, “Smoke tastes bad.” We can sense these things unconsciously without thinking. Therefore we CAN sense stimuli below our absolute stimulus. We can also be affected by stimuli so weak as to be unnoticed.
4.Difference Threshold is the minimum difference between 2 stimuli required for detection 50% of the time. People are less likely to realize slight differences in changes. For example, addition of 10 gram of weight in 1 kilogram weight. This is proven by the Weber’s law, the principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage.
Sensory Adaptation
Sensory Adaptation is the diminished sensitivity as a consequence of constant stimulation. For example, when you put on a ring, you will feel it, but when you put it on your finger for a while, you won’t
The phenomenon of sensory adaptation focuses our attention on informative changes in stimulation by diminishing our sensitivity to constant or routine odors, sounds, and touches.
Transduction is the conversion of one form of energy into another. In sensation, the transforming of stimulus energies into neural impulses. Our eyes receive light energy and transduce the energy into neural messages so that the object is visible.
The Stimulus Input: Light Energy
Pulses of electromagnetic energy is what strikes our eyes and what our visual system experiences as color. There are 2 physical characteristics of light and sound hlep determine our sensory experience of them.
1. Wavelength is the distance from one wave peak to the next that determines its hue (hue: the dimension of color that is determined by the wavelength of the light).
2. Intensity is the amount of energy in a light or sound wave, which we perceive as brightness our loudness, as determined by the wave’s amplitude.
The Eye
Light enters through the cornea which is the out-layer that protects your eyes, then passes pupil. Iris regulates the amount of light that is allowed in to our pupils. After pupil, lens receives the light. It focuses the incoming rays into an image on the eye’s light-sensitive back surface. This process of changing its curvature is called accommodation.
For visuals, acuity, Farsightedness and nearsightedness is a important concept. Acuity is the sharpness of vision that can be affected by small distortions in the shape of the eye. Nearsightedness is a condition in which nearby objects are seen more clearly than distant objects because distant objects focus in front of the retina. Farsightedness is exact opposite to nearsightedness, a condition in which faraway objects are seen more clearly than near objects because the image of near object is focused behind the retina.
Inside the retina there are two receptors called rods and cones. Rods detect black, white, and gray, which is necessary for peripheral and twilight vision, when cones don’t respond. Cones are receptor cells that are concentrated near the center of the retina and that function in daylight or in well-lit conditions. Cones are clustered around the fovea, the central focal point in the retina, around which the eye’s cones cluster. Nearly million messages can be sent by the optic nerve at once, but there is sometimes a spot called blind spot, the point at which the optic nerve, the nerve that carries neural impulses from the eye to the brain, leaves the eye, creating blind spot because there are not receptors.
Visual Information Processing
Neurons in the optic nerves run to the thalamus, where they synapse with neurons that run to the visual cortex.
Even in the dark, ganglion cells have a slow, steady rate of firing.
Diffuse light directed on the retina has little effect on this rate.
But a tiny spot of light falling on a small circular area of the retina can greatly increase the firing rate of some ganglion cells (LEFT) while
a spot directed around the perimeter of such an "on" area suppresses that ganglion cell (CENTER).
Light shining on both areas produces no effect (RIGHT).
Other ganglion cells have a central "off" area surrounded by an "on" area.
Feature Detection: Feature detection is a process by which specialized nerve cells in the brain respond to specific features of a visual stimulus, such as lines, edges, angle, or movement.
Parallel Processing:Parallel processing is the ability of the brain to simultaneously process incoming stimuli. This becomes most important in vision, as the brain divides what it sees into four components: color, motion, shape, and depth. These are individually analyzed and then compared to stored memories, which helps the brain identify what you are viewing. The brain then combines all of these into one image that you see and comprehend. This is a continual and seamless operation.The advantage of parallel processing is that it allows the brain to simultaneously identify different stimuli and allow for quick and decisive action.
Color Vision
Color vision is the capacity of an organism or machine to distinguish objects based on the wavelengths (or frequencies) of the light they reflect or emit. The nervous system derives color by comparing the responses to light from the several types of cone photoreceptors in the eye. These cone photoreceptors are sensitive to different portions of the visible spectrum.
Helmholtz trichromatic theory is the theory that the retina contains three different color receptors . One most sensitive to red, one to green, one to blue, which when stimulated in combination can produce the perception of any color.
Color Constancy: is a perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the object. A green apple for instance looks green to us at midday, when the main illumination is white sunlight, and also at sunset, when the main illumination is red. This helps us identify objects.
Hearing: Like other senses, audition (hearing) is highly adaptive.
The Stimulus Input: Sound Waves
How waves travel from one lace to another: The resulting waves of compressed and expanded air are like the ripples on a pond circling out from where a stone has been tossed. The ears then transform them into never impulses, which our brain decodes as sounds.
Frequency, is the number of complete wavelengths that pass a point in a given time, and the frequency determines the pitch, a tone’s highness or lowness.
The Ear
How do we convert sound waves into neural activity?
First, the visible outer ear channels the sound waves through the auditory canal to the eardrum, a tight membrane that vibrates with the waves. The middle ear then transmits the eardrum’s vibrations through a piston made of three tiny bones to a snail shaped tube in the inner ear called the cochlea. The incoming vibrations cause the cochlea’s membrane to vibrate the fluid that fills the tube. This motion causes ripples in the basilar membrane. Lastly, the rippling of the basilar membrane bends these hair cells.
How do we perceive pitch?
There are two theories about perceiving pitch.
1. Place theory by Hermann von Helmholts presumes that we hear different pitches because different sound waves trigger activity at different places along the cochlea’s basilar membrane.
2. Frequency theory suggest that an alternative explanation for how we etect pitch. It is a theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense it’s pitch.
How do we locate sounds?
Why don’t we have one ear? We have two ears that allows us to enjoy stereophonic (3D) hearing. The slightly different messages sensed by the two microphones used in creating a stereophonic recording mimic the slightly different sound messages received by our two ears.
Hearing Loss and Deaf Culture
There are two possible reason for hearing loss.
1. Conduction hearing loss: hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea.
2. Sensorineural hearing loss: Hearing loss caused by damage to the cochlea’s receptor cells or to the auditory nerves; aka nerve deafness.
The Other Senses
Touch: Even though touch is not the first sense to come to mind, it is very important. Your sense of touch is found all over. This is because your sense of touch originates in the bottom layer of your skin called the dermis. They do this by carrying the information to the spinal cord, which sends messages to the brain where the feeling is registered.
The nerve endings in your skin can tell you if something is hot or cold. They can also feel if something is hurting you. Your body has about twenty different types of nerve endings that all send messages to your brain. However, the most common receptors are heat, cold, pain, and pressure or touch receptors. Pain receptors are probably the most important for your safety because they can protect you by warning your brain that your body is hurt.
Although no theory of pain explains all the available findings, gate control theory still provides a useful model. It is a theory that the spinal cord contains a neurological gate that blocks pain signals or allows them to pass on to the brain. The gate is opened by the activity of pain signals traveling up small nerve fibers and is closed by activity in larger fibers or by info coming from the brain.
Taste buds probably play the most important part in helping you enjoy the many flavors of food. Your taste buds can recognize four basic kinds of tastes: sweet, salty, sour, and bitter. The salty/sweet taste buds are located near the front of your tongue; the sour taste buds line the sides of your tongue; and the bitter taste buds are found at the very back of your tongue.
Smell not only adds to our perception of taste, it also changes it. This is called a sensory interaction, the principle that one sense may influence another, as when the smell of food influences its taste.
Smell: How do you smell things?
As you breathe in, the air enters through your nostrils which contain tiny little hairs that filter all kinds of things. These little hairs are called cilia and you can pretend that they sweep all the dirt out of the nasal cavity, which is the big place the air passes through on it's way to the lungs. After passing through the nasal cavity, the air passes through a thick layer of mucous to the olfactory bulb. There the smells are recognized because each smell molecule fits into a nerve cell like a lock and key. Then the cells send signals along your olfactory nerve to the brain. At the brain, they are interpreted.
Body Position and Movement
Human beings have millions of position and motion sensors which are all over our bodies: muscles, tendons, and joints.
The sense of our body movement is called kinesthesis. A companion, vestibular sense monitors the head’s position and movement.
Related terms and concepts: insert links to other pages on The Neuron here
  • Rods
  • Perception
  • audition
  • gate-control theory
  • kinesthesis

Related websites: insert links to external websites here
Sources: insert WAPA style citations here
  1. Myers, D (2004). Psychology. New York, NY: Worth Publishers.
  2. Swaraajk (2006).
  3. koilk (2005).
Edited by: Erica
Date of last edit:0924 2009

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