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Sensation & Perception

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Leah Winger

on 19 April 2016

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Transcript of Sensation & Perception

Sensation & Perception
Chapter 3
What is sensation?
the activation of receptors in the various sense organs (eyes, ears, skin, nose, and tongue
Color Blindness
Perception
Structure of the Eye
Dark adaptation
: the recovery of the eye's sensitivity to visual stimuli in darkness after exposure to bright lights.
Rods
detect changes in brightness but do not see color and function best in low levels of light.

Light adaptation
: the recovery of the eye's sensitivity to visual stimuli in light after exposure to darkness.
Cones
are sensitive to colors and work best in bright light.
Trichromatic theory
: theory of color vision that proposes three types of cones: red, blue, and green. All colors would be perceived as combinations of these three.
Opponent-process theory:
assumes four primary colors of red, green, blue, and yellow. Colors are arranged in pairs, and when one member of a pair is activated, the other is not.
Afterimages occur when a visual sensation persists for a brief time even after the original stimulus is removed.




Sensory Thresholds
Examples:
Habituation and Sensory Adaptation
Visible Spectrum
Properties of Light
What are sensory receptors?
specialized forms of neurons that are activated by different stimuli or energy such as light and sound instead of neurotransmitters
Subliminal
: Below the threshold. Strong enough to activate the sensory receptors but not strong enough for the person to be aware of it. Has not been proven effective in advertising.

Just Noticeable Difference
: the smallest difference between two stimuli.

Absolute
: the smallest amount of energy needed for conscious detection of a stimulus at least half of the time it is present.
candle flame at 30 miles on a clear, dark night
a bee's wing falling on the cheek from 1 cm above
the tick of a watch 20 ft away in a quiet room
One drop of perfume diffused throughout a 3 room apartment
1 teaspoon of sugar in 2 gallons of water
Habituation
: when the brain stops attending to constant, unchanging stimuli (cognitive).

Sensory Adaptation
: the tendency of sensory receptor cells to become less responsive to a stimulus that is unchanging


Einstein first introduced "wave packets' called photons. 3 aspects to our perception on light: brightness, color, and saturation.


Brightness is determined by the amplitude of the wave - how high or how low the wave actually is
the higher the wave, the brighter the light will be
low waves are dimmer
Color or hue, is determined by the length of the wave
long wavelengths are found at the red end of the visible spectrum of light that is visible to the human eye
shorter wavelengths are found at the blue end
Saturation is the purity of the color people see
mixing in black or gray would lessen the saturation
Light enters the eye through the cornea and pupil. The iris controls the size of the pupil. From the pupil, light passes through the lens to the retina, where it is transformed into nerve impulses. The nerve impulses travel to the brain along the optic nerve.
Structure of the Eye: The Back
1. Light passes through ganglion and bipolar cells
2. It reaches and stimulates the rods and cons
3. Nerve impulses from the rods and cones travel along a nerve pathway to the brain
Retina
: final stop for light in the eye. Has 3 layers: ganglion cells, bipolar cells, and photoreceptors
Rods
: visual sensory receptors found at the back of the retina. Responsible for noncolor sensitivity to low levels of light
Cones
: visual sesnory receptors found at the back of the retina. Responsible for color vision and sharpness of the vision.
Nearsightedness
(myopia): the shape of the eye causes the focal point to fall short of the retina
Farsightedness
(hyperopia): the focus point is behind the retina
Light falling on the left side of each eye’s retina (from the right visual field, shown in yellow) will stimulate a neural message that will travel along the optic nerve to the visual cortex in the occipital lobe of the left hemisphere.

Notice that the message from the temporal half of the left retina goes directly to the left occipital lobe, while the message from the nasal half of the right retina crosses over to the left hemisphere (the optic chiasm is the point of crossover).


The optic nerve tissue from both eyes joins together to form the left optic tract before going on to the left occipital lobe.

For the left visual field (shown in blue), the messages from both right sides of the retinas will travel along the right optic tract to the right visual cortex in the same manner.

Stare at the white dot in the center of this oddly colored flag for about 30 seconds. Now look at a white piece of paper or a white wall. Notice that the colors are now the normal, expected colors of the American flag. They are also the primary colors that are opposites of the colors in the picture and provide evidence for the opponent-process theory of color vision.

Monochrome colorblindness
: a condition in which a person's eyes either have no cones or have cones that are not working at all

Red-green colorblindness
: either the red or the green cones are not working
Sound
Wavelength
: interpreted as frequency or pitch (high, medium, or low)

Sound has three aspects:
pitch
(frequency): uses
hertz
to measure the cycles or waves per second
amplitude
(loudness): how soft or loud a sound is
timbre
(purity): a richness in the tone of the sound

Structure of the Ear
Auditory canal
: short tunnel that runs from the pinna to the eardrum (tympanic membrane)
Eardrum
: thin section of skin that tightly covers the opening into the middle part of the ear. When sound waves hit the eardrum, it vibrates and causes three tiny bones (hammer, anvil, and the stirrup) in the middle ear to vibrate
Cochlea
: snail-shaped structure of the inner ear that is filled with fluid
Organ of Corti
: rests in the basilar membrane
contains receptor cells for sense of hearing
Auditory nerve
: bundle of axons from the hair cells in the inner ear receives neural message
from the organ of Corti



Sound enters the ear through the visible outer structure, or pinna, and travels to the eardrum and then to the small bones of the middle ear.


rests on the oval window, causing the cochlea and basilar membrane to vibrate with sound.
The organ of Corti on the basilar membrane contains the auditory receptors, which send signals to the brain about sound qualities as they vibrate.
Pitch Theories
Location of the hair cells on the organ of Corti corresponds to different pitches of sound. Explains pitch above 1000 Hz.

Speed with which the basilar membrane vibrates corresponds to different pitches of sound. Explains pitch below 1000 Hz.

Neurons take turns firing for sounds above 400 Hz and below 4000 Hz

Hearing Loss
Conduction hearing impairment
is caused by damage to the outer or middle ear structures



Nerve hearing impairment
is caused by damage to the inner ear or auditory pathways in the brain.


Damaged Eardrum
:
would prevent sound waves from being carried into the middle ear properly


Damage to the bones
of the Middle Ear
:
sounds cannot be conducted from
the eardrum to the cochlea
In a cochlear implant, a microphone implanted just behind the ear picks up sound from the surrounding environment. A speech processor, attached to the implant and worn outside the body, selects and arranges the sound picked up by the microphone.

The implant itself is a transmitter and receiver, converting the signals from the speech processor into electrical impulses that are collected by the electrode array in the cochlea and then sent to the brain.

Gustation
is the sense of taste.
Taste buds
(taste receptor cells in mouth; responsible for sense of taste) receive molecules of substances, which fit into receptor sites.

sweet
Sour
Salty
bitter
umami

"brothy"
sight
hearing
taste
smell
touch
Olfaction
is the sense of smell.

The olfactory receptors in the upper part of the nasal passages receive molecules of substances and create neural signals that then go to the olfactory bulbs under the
frontal lobes
.



This drawing shows the nerve fibers inside the nasal cavity that carry information about smell directly to the olfactory bulb just under the frontal lobe of the brain (shown in green).


The cells in the nose that process smell. The olfactory bulb is on top. Notice the cilia, tiny hairlike cells that project into the nasal cavity. These are the receptors for the sense of smell.
At least 1,000 olfactory receptors!!!
What is thought of as the sense of touch is really several sensations, originating in several different places in—and on—the body.
Skin senses:
touch, pressure, temperature, pain
sensory receptors in the skin
Gate-control theory
: pain signals must pass through a “gate” located in the spinal cord
Kinesthetic sense:
location of body parts in relation to one another
Vestibular senses:
movement, body position
Sensory conflict theory: an explanation of motion sickness in which the information from the eyes conflicts with the information from the vestibular senses. Results in dizziness, nausea, and other physical discomforts


Somesthetic Senses
"soma"=body
“esthetic”=feeling

The gate-control theory of pain states that when receptors sensitive to pain are stimulated, a neurotransmitter called substance P is released into the spinal cord, activating other pain receptors by opening “gates” in the spinal column and sending the message to the brain.

The kinesthetic senses allow the brain to know the position and movement of the body through the activity of special receptors responsive to movement of the joints and limbs.
 
The vestibular sense also contributes to the body’s sense of spatial orientation and movement through the activity of the otolith organs (up-and-down movement) and the semicircular canals (movement through arcs).

Motion sickness is explained by sensory conflict theory, in which information from the eyes conflicts with information from the vestibular sense, causing nausea.
Method by which sensations are organized and interpreted

Size constancy:
the tendency to interpret an object as always being the same actual size, regardless of its distance

Shape constancy:
the tendency to interpret the shape of an object as being constant, even when its shape changes on the retina

Brightness constancy:
the tendency to perceive the apparent brightness of an object as the same even when the light conditions change


Gestalt Principles
Figure–ground:
the tendency to perceive objects, or figures, as existing on a background
Proximity:
the tendency to perceive objects that are close to one another as part of the same grouping.
Similarity
: tendency to perceive things that look similar to each other as being part of the same group
Closure:
tendency to complete figures that are incomplete
Continuity:
tendency to perceive things as simply as possible with a continuous pattern rather than with a complex, broken-up pattern
Contiguity:
tendency to perceive two things that happen close together in time as being related





Depth perception
: The ability to perceive the world in three dimensions
Monocular
: cues for perceiving depth based on one eye only
Binocular
: cues for perceiving depth based on both eyes

Monocular
Linear Perspective
: the tendency for parallel lines to appear to converge on each other


Monocular
Relative Size
: perception that occurs when objects that a person expects to be of a certain size appear to be small and are, therefore, assumed to be much farther away

Monocular
Overlap
: the assumption that an object that appears to be blocking part of another object is in front of the second object and closer to the viewer

Monocular
Aerial
(atmospheric) perspective: the haziness that surrounds objects that are farther away from the viewer, causing the distance to be perceived as greater

Monocular
Texture Gradient
: the tendency for textured surfaces to appear to become smaller and finer as distance from the viewer increases

Binocular
Convergence
: the rotation of the two eyes in their sockets to focus on a single object, resulting in greater convergence for closer objects and lesser convergence if objects are distant

Binocular
Binocular Disparity
: the difference in images between the two eyes, which is greater for objects that are close and smaller for distant objects

LEFT FIGURE: Convergence is a depth cue that involves the muscles of the eyes. When objects are far away, the eye muscles are more relaxed; when objects are close, the eye muscles move together, or converge.



RIGHT FIGURE: Binocular disparity. Because your eyes are separated by several centimeters, each eye sees a slightly different image of the object in front of you. In A, the object is far enough away that the difference is small. In B, while the object is closer, there is a greater difference between what each eye sees. The brain interprets this difference as the distance of the object.
Illusions
are perceptions that do not correspond to reality or are distortions of visual stimuli.

The Muller-Lyer Illusion

Moon illusion: the moon on the horizon appears to be larger than the moon in the sky
apparent distance hypothesis

Hermann Grid

Illusions of Motion
Autokinetic Effect
: a small, stationary light in a darkened room will appear to move or drift because there are no surrounding cues to indicate that the light is not moving
Stroboscopic Motion
: seen in motion pictures, in which a rapid series of still pictures will appear to be in motion
Phi Phenomenon
: lights turned on in a sequence appear to move
Rotating Snakes
: due in part to eye movements



What influences perception?
Perceptual set
or
expectancy
refers to the tendency to perceive objects and situations in a particular way because of
prior experiences
.

Top-down processing
involves the use of
preexisting knowledge
to organize individual features into a unified whole.

Bottom-up processing
involves the
analysis of smaller features
, building up to a complete perception.


Electromagnetic Spectrum
How Do We Interpret Those Colors?

If you think the dress is in shadow, your brain may remove the blue cast and perceive the dress as being white and gold
If you think the dress is being washed out by bright light, your brain may perceive the dress as a darker blue and black
If the photograph showed more of the room, or if skin tones were visible, there might have been more clues about the ambient light.
red paired with green and blue with yellow
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