Sensation
Three characteristics of our senses
• Transduction always occurs; Physical energy is converted into electrical signals to be sent to the
brain for processing.
• Adaptation occurs; This refers to the decreasing response of the sense organs, the more they are
exposed to a continuous level of stimulation (sensation).
• Sensations versus perceptions: Perceptions are brain processed sensations.
Spectrum of light - The electromagnetic spectrum is the spectrum of all forms of light across the many
frequencies it travels at. The light we see is a small, slim sliver of the electromagnetic spectrum. It is
significant to us, because it is through these few wavelengths of light all the richness of the world is
conveyed to us. Light is Invisible if the wavelength is too short or too long.
Notes on the structure & function of the eye.
The Image is reversed in the eye, this is "fixed" by the brain.
Light waves must be focused to be seen. the Cornea focus the light waves into a narrower beam.
The Pupil allows light into the interior of the eye.
The Iris controls the amount of light allowed to enter.
The Lens focus, focus , focus
The Retina - begins transduction
The Eyeball's shape affects vision
Nearsightedness - eyeball to long
Farsightedness - eyeball to short
Retina: a miniature camera-computer has two types of photoreceptors:
Rods to see in dim light
Cones to see color
Transduction (light to nerve impulses) occurs in the retina. The transmission path to the brain is
the optic nerve. There is a blind spot where the optic nerve exits the eye but it is not noticed
because the eye is constantly moving.
Visual pathways: eye to brain
- The optic nerve connects to the thalamus for initial processing. Next stop the occipital lobe.
- The primary visual cortex in the occipital lobe using specialized cells adds detail.
- The visual association areas in the occipital lobe add meaning and complete the process
producing vision.
Color vision - theories
The trichromatic theory of color vision is based on the premise that there are three classes of
one receptors serving color vision. One of the more important empirical aspects of this theory
is that it is possible to match all of the colors in the visible spectrum by the appropriate mixing
of the three primary additive colors red, green, & blue. When these are mixed equally
white is produced.
FYI: The three primary subtractive (pigment) colors are red, blue, & yellow. When pigment colors
are mixed equally black is produced.
The Opponent-Process theory
Afterimages show opponent pairs: red-green & yellow-blue
When excited or inhibited, ganglion & thalamic cells signal
one of the pair colors.
Physiology shows: Trichromatic + Opponent processes are combined.
Color blindness
Monochromats - no cones = no color
Dichromats - cannot tell red from green
The Ear: Audition
Sound waves have;
Loudness (Amplitude)
Pitch (Frequency)
Measuring sound waves
A decibel is a relative measurement of the intensity of a sound wave. A quiet whisper at 1 meter
is about 10 decibels, noise from a motor car at 5 meters is about 70 decibels and noise from a large
jet plane at 40 meters is about 110 decibels.
To many decibels for to long causes deafness.
Outer ear:
External ear - composed of the visible parts of the ear.
Auditory canal - the canal leading to the eardrum.
Tympanic membrane - the membrane in the ear that vibrates to sound.
The Tympanic membrane is the eardrum!
Middle ear:
Ossicles (AW-sick-culls) - three small bones articulated to each other in the middle ear: malleus (hammer),
incus (anvil), & stapes (stirrup). They conduct the vibrations of the tympanic membrane to the inner ear.
Oval window - end membrane
Inner ear:
Cochlea - the snail-shaped tube (in the inner ear coiled around the modiolus) where sound vibrations are
converted into nerve impulses by the Organ of Corti
The auditory receptors, called hair cells are bend by the basilar membrane generating nerve impulses.
Auditory nerve
Auditory brain areas
Primary auditory cortex
Auditory association area
Auditory cues
Calculating direction of a sound - timing difference between the ears.
Calculating pitch - by Frequency & Place
Calculating loudness - by rate
Sensation - Vestibular System
The Vestibular System is the system in the body that is responsible for maintaining
the body’s orientation in space, balance, and posture; regulates locomotion & other movements
and keeps objects in visual focus as the body moves.
The Vestibular System is implemented by an organ of the inner ear containing three semicircular
ducts (canals) at right angles to one another. These help keep the body balanced, sense the
position of head, and keep the head upright.
Problems with the Vestibular System can produce:
- Motion sickness (nausea)
- Meniere's disease (caused by viral infection) an abnormality of the inner ear causing a host of symptoms,
including vertigo or severe dizziness, tinnitus or a roaring sound in the ears, fluctuating hearing loss, and
the sensation of pressure or pain in the affected ear.
- Vertigo (dizziness)
Sensation - Chemical Senses
Five basic tastes: sweet, salty, sour, bitter, & umami
The surface of the tongue is trenched, within them are the taste buds the receptors for taste.
Flavor is the result of the combination of taste & smell.
Smell or olfaction, Functions of olfaction;
intensify the taste of food
warn of bad foods
elicit strong memories
Sensation - Touch
Ψ The outermost layer of the skin has no sensory receptors.
Ψ The sense of touch comes from a half-dozen miniature sensors located in the inner layers
of the skin. Major sensors include; hair receptors, free nerve endings & Pacinian corpuscles.
Ψ The somatosensory cortex which is located in the parietal lobe of the brain transforms nerve
impulses into the sensations of touch, temperature & pain.
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Topics in Psychology
Robert C. Gates