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Vision is the dominant sense in human beings. Sighted people use vision to gather information about their environment more than any other sense. The process of vision involves several steps.  

Step 1: Gathering light

Step 2: Within the eye

Cornea -The transparent protective coating over the front part of the eye  

Pupil -small opening in the iris through which light enters the eye.  
-colored part of the eye.  
-transparent part of the eye inside the pupil that focuses light onto the retina  
-lining of the eye containing receptor cells that are sensitive to light

Step 3: Transduction

Transduction –process by which sensory signals are transformed into neural impulses  
Receptor cell
-Specialized cell that responds to a particular type of energy.  
-Receptor cells in the retina responsible for night vision and perception of brightness.  
-Receptor cells in the retina responsible for color vision  
-Area of the retina that is the center of the visual field  
Optic nerve
- The bundle of axons of ganglion cells that carries neural messages from each eye to the brain.  
Blind spot
- Place on the retina where the axons of all the ganglion cells leave the eye and where there are no receptors Optic chiasm -Point near the base of the brain where some fibers in the optic nerve from each eye cross to the other side of the brain

Step 4: In the Brain

Theories or color vision-

Trichromatic theory -Theory of color vision that holds that all color perception derives from three different color receptors in the retina

Opponent-process theory - Theory of color vision that holds that three sets of color receptors respond in an either/or fashion to determine the color you experience

Colorblindness -Partial or total inability to perceive hues.

Trichromats -People who have normal color vision

Monochromats -People who are totally color blind

Dichromats - People who are blind to either red-green or yellow-blue  


The ears contain structures for both the sense of hearing and the sense of balance. The eighth cranial nerve (vestibulocochlear nerve made up of the auditory and vestibular nerves) carries nerve impulses for both hearing and balance from the ear to the brain.

Amplitude – the height of the wave , determines the loudness of the sound, measured in decibels  
- The number of cycles per second in a wave; in sound, the primary determinant of pitch  
Hertz (Hz)
- Cycles per second; unit of measurement for the frequency of waves  
- Auditory experience corresponding primarily to frequency of sound vibrations, resulting in a higher or lower tone Decibel -The magnitude of a wave; in sound the primary determinant of loudness of sounds

 Parts of the ear-  

Ear canal –
also called the auditory canal  

Hammer, anvil, stirrup
- The three small bones in the middle ear that relay vibrations of the eardrum to the inner ear  

Oval window - Membrane across the opening between the middle ear and inner ear that conducts vibrations to the cochlea  
Round window
- Membrane between the middle ear and inner ear that equalizes pressure in the inner ear.
- Part of the inner ear containing fluid that vibrates which in turn causes the basilar membrane to vibrate.  
Basilar membrane
-Vibrating membrane in the cochlea of the inner ear; it contains sense receptors for sound  
Organ of Corti
-Structure on the surface of the basilar membrane that contains the receptors cells for hearing  
Auditory nerve
-The bundle of neurons that carries signals from each ear to the brain

 PITCH THEORIES- As with color vision, two different theories describe the two processes involved in hearing pitch: place theory and frequency theory.

Place theory -Theory that pitch is determined by the location of greatest vibration of the basilar membrane

Frequency theory -Theory that pitch is determined by the frequency wigh which hair cells in the cochlea fire


Hearing Loss

People can lose all or some of their ability to hear because of loud noises, infections, head injuries, brain damage and genetic diseases. Hearing loss is common in older people. There are several types of hearing loss:

  • Conductive Hearing Loss: occurs when sound vibrations from the tympanic membrane to the inner ear are blocked. This may be caused by ear wax in the auditory canal, fluid buildup in the middle ear, ear infections or abnormal bone growth.
  • Sensorineural Hearing Loss: occurs when there is damage to the vestibulocochlear (auditory) nerve. This type of hearing loss may be caused by head injury, birth defects, high blood pressure or stroke.

  • Presbycusis: occurs because of changes in the inner ear. This is a very common type of hearing loss that happens gradually in older age.

  • Tinnitus: people with tinnitus hear a constant ringing or roaring sound. The cause of this ringing cannot always be found. Some cases of tinnitus are caused by ear wax, ear infections or a reaction to antibiotics, but there are many other possible causes of this disorder.


When our skin is indented, pierced, or experiences a change in temperature, our sense of touch is activated by this energy.

Gate control theory - Theory that a ‘neurological gate in the spinal cord controls the transmission of pain messages to the brain  



Taste buds

Humans sense four different tastes: sweet, salty, sour, and bitter  

All other tastes come from a combination of these four basic tastes. Actually, a fifth basic taste called "Umami" has recently been discovered. Umami is a taste that occurs when foods with glutamate (like MSG) are eaten. Different parts of the tongue can detect all types of tastes. Morever, the simple tongue "taste map" that is found in many textbooks has been criticized for several reasons.

The actual organ of taste is called the "taste bud". Each taste bud (and there about about 10,000 taste buds in humans) is made up of many (between 50-150) receptor cells. Receptor cells live for only 1 to 2 weeks and then are replaced by new receptor cells. Each receptor in a taste bud responds best to one of the basic tastes. A receptor can respond to the other tastes, but it responds strongest to a particular taste.




The Nose Knows


The smells of a rose, perfume, freshly baked bread and cookies...these smells are all made possible because of your nose and brain. The sense of smell, called olfaction, involves the detection and perception of chemicals floating in the air. Chemical molecules enter the nose and dissolve in mucous within a membrane called the olfactory epithelium. In humans, the olfactory epithelium is located about 7 cm up and into the nose from the nostrils.

Olfactory epithelium - Nasal membranes containing receptor cells sensitive to odors  
- Chemical that communicates information to other organisms through smell

VESTIBULAR SENSE tells us about how our body is oriented in space.

Semicircular canals - Structure in the inner ear particularly sensitive to body roataion.

Vestibular sacs - Sacs in the inner ear that are responsible for sensing gravitation and forward, backward, and vertical movement

KINESTHETIC SENSES -Senses of forces and movement of muscles

Stretch receptors -Receptors that sense muscle stretch and contraction

Golgi tendon organs -Receptors that sense movement of the tendons, which connect muscle to bone.



Absolute threshold -The least amount of energy that can be detected as a stimulation 50 percent of the time

Subliminal- stimuli below our absolute threshold

Difference threshold -The smallest change in stimulation that can be detected 50 percent of the time

just-noticeable difference – the smallest amount of change needed in a stimulus before we detect a change

Weber’s Law -The principle that the just noticeable difference for any given sense is a constant proportion of the stimulation being judged.


Psychologists use several theories to describe how we perceive the world.

Signal detection theory- investigates the effects of the distractions and interference we experience while perceiving the world.

Response criteria

False positive

Top-Down Processing – we perceive by filling in gaps in what we sense


Perceptual set


Bottom-up Processing, also called feature analysis – we use only the features of the object itself to build a complete perception


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