Exit Table of Contents Chapter 4 Sensation and Perception.

Exit Table of Contents

Chapter 4

Sensation and Perception



Chemical senses Smell Taste

Skin senses Touch Pressure Temperature

Kinesthesis & Vestibular senses

ESP

Life Connections: Pain Methods for coping

with pain



Sensation: is the stimulation of sensory receptors and the

transmission of sensory information to the central nervous system.

Perception: is an active process in which sensations are organized and

interpreted to form an inner representation of the world. Five Senses:

Vision. Hearing. Smell. Taste. Touch.


Thresholds

Absolute threshold: refers to the weakest amount of a stimulus that a person can distinguish from no stimulus at all 50% of the time. Examples include:

Vision: candle flame viewed from about 30 miles on a clear, dark night.

Hearing: a watch ticking from about 20 feet away in a quiet room.

Difference Threshold: the minimum difference in magnitude of two stimuli required to tell them apart 50% of the time (“just noticeable difference”).


Signal-Detection Theory

Considers the human aspects of sensation, and perception

Assumes that the relationship between a physical stimulus and a sensory response is not just mechanical.

Other factors include: Training (learning). Motivation (desire to perceive). Psychological states such as fatigue or

alertness.


Sensory Adaptation

the sensory process of adjustment. Positive adaptation

Becoming more sensitive to stimulation. Negative adaptation

Becoming less sensitive to stimulation.


Vision

More than half of our brain’s cerebral cortex is devoted to visual functions.


The Eye

Light first passes through the transparent cornea. The amount of light that is allowed to enter is

controlled by the muscle called the iris (the colored part of the eye).

The actual opening in the iris is called the pupil. The lens adjusts or accommodates to the image

by changing its thickness. The thickness permits a clear image of the object to be projected onto the retina.


Figure 4.2 The Human Eye. In both the eye and a camera, light enters through a narrow opening and is projected onto a sensitive surface. In the eye, the photosensitive surface is called the retina, and information concerning the changing images on the retina is transmitted to the brain. The retina contains photoreceptors called rods and cones. Rods and cones transmit sensory input back through the bipolar neurons to the ganglion neurons. The axons of the ganglion neurons form the optic nerve, which transmits sensory stimulation through the brain to the visual cortex of the occipital lobe.


The Eye

Rods and Cones Cones are most densely packed in a small spot

at the center of the retina called the fovea. Visual acuity (sharpness and detail) is greatest at this

spot. Rods are most dense toward the periphery of

the retina. Rods allow us to see in black and white. Cones provide color vision. In contrast to visual acuity is the blind spot

which is the part of the optic nerve which leaves the eye.


Light Adaptation

Dark adaptation: the process of adjusting to lower lighting

conditions. Light adaptation

Adapting to brighter lighting takes place much more rapidly.


Figure 4.5 Dark Adaptation. This illustration shows the amount of light necessary for detection as a function of the amount of time spent in the dark. Cones and rods adapt at different rates. Cones, which permit perception of color, reach maximum dark adaptation in about ten minutes. Rods, which permit perception of dark and light only, are more sensitive than cones. Rods continue to adapt for up to about 45 minutes.


Color Vision: Two theories

Trichromatic Theory. Helmholtz suggested that the retina in the eye must have

three different types of color photoreceptors or cones. Is theory works well to explain color blindness.

Opponent-Process theory. Hering proposed that there are three types of color

receptors but they don’t respond just to red, green and blue-violet.

They are pairs including red-green; blue-yellow; and a type that perceives differences in brightness.

These pairs of receptors are what make afterimages possible.


Color Blindness

If you can discriminate among the colors of the visible spectrum, you have normal color vision and are labeled a trichromat.

People who are totally color blind are called monochromats.

Partially color-blind people are called dichromats as they can discriminate only among two colors-red and green or blue and yellow-and the colors derived from mixing these colors. Partial color blindness is a sex-linked trait that

affects mostly males.


Figure 4.10 Plates from a Test for Color Blindness. Can you see the numbers in these plates from a test for color blindness? A person with red–green color blindness would not be able to see the 6, and a person with blue–yellow color blindness would probably not discern the 12. (Caution: These reproductions cannot be used for actual testing of color blindness.)


Color Vision

Afterimages. Persistent sensations of color are followed by

perception of the complimentary color when the first color is removed.


Figure 4.9 Three Cheers for the…Green, Black, and Yellow. Don’t be concerned. We can readily restore Old Glory to its familiar hues. Place a sheet of white paper beneath the book and stare at the black dot in the center of the flag for at least 30 seconds. Then remove the book. The afterimage on the paper beneath will look familiar.


CONTROVERSY IN PSYCHOLOGY: When Light With Different Wavelengths

Stimulate The Retina

Research suggests that each theory of color vision is partially correct. The cones may be as Helmholtz claimed. The transmission of the signals to the brain

are as Hering proposed.


Visual Perception

Visual perception is the process by which we organize or make sense

of the sensory impressions caused by the light that strikes our eyes.

involves our knowledge, expectations, and motivations.

is an active process through which we interpret the world around us.

Gestalt psychologists refer to closure as being the integration of disconnected pieces of information

into a meaningful whole, or the tendency to perceive a complete or whole figure

even when there are gaps in the sensory input.


Figure 4.11 Closure. Meaningless splotches of ink or a horse and rider? This figure illustrates the Gestalt principle of closure.


Perceptual Organization

Gestalt psychologists are interested in the way we integrate bits and pieces of sensory stimulation into meaningful wholes. Figure-Ground Perception.

When figure-ground relationships are ambiguous, or capable of being interpreted in various ways, our perceptions tend to be unstable, shifting back and forth.


Figure 4.13 The Rubin Vase. A favorite drawing used by psychologists to demonstrate figure–ground perception. Part A is ambiguous, with neither the vase nor the profiles clearly the figure or the ground. In part B, the vase is the figure; in part C, the profiles are.


Figure 4.14 Necker Cube. Ambiguity in the drawing of the cube makes perceptual shifts possible. Therefore, the darker tinted surface can become either the front or back of the cube.



Other Gestalt Rules for Organization: Proximity:

nearness. Similarity:

we perceive similar objects as belonging together. Continuity:

we perceive a series of points or a broken line as having unity.

Common Fate: elements seen as moving together are perceived

as belonging together.


Figure 4.15 Some Gestalt Laws of Perceptual Organization. These drawings illustrate the Gestalt laws of proximity, similarity, continuity, and closure.



Top-Down Versus Bottom-Up Processing. Top-Down Processing

Use the larger pattern to guide subordinate tasks. Bottom-Up processing

Begin with bits and pieces of information and become aware of the pattern formed only after you’ve worked on it a while.


Perception of Motion

Visual perception of movement is based on change of position relative to other objects.

Types of apparent movement (illusions of movement). The Autokinetic Effect

is the tendency to perceive a stationary point of light as moving in a dark room.

Stoboscopic Motion is what makes motion pictures possible. The illusion of movement is provided by the presentation of a

rapid progression of images of stationary objects. The Phi Phenomenon

occurs as the on-off process of lights is perceived as movement.

We tend to perceive a series of points as having unity, so each series of lights is perceived as a moving line.


Depth Perception

Monocular Cues: cues that can be perceived by one eye. Perspective:

distances between far off objects appear to be smaller than equivalent distances between nearby objects.

Relative size: the fact that distant objects look smaller than nearby objects

of the same size. Clearness of an object:

We sense more details of nearby objects. Interposition:

Nearby objects can block our view of more distant objects. Interposition is placing of one object in front of another.


Figure 4.17 The Effects of Interposition. The four circles are all the same size. Which circles seem closer? The complete circles or the circles with chunks bitten out of them?


Depth Perception

Monocular Cues continued. Shadows:

opaque objects block light and produce shadows giving us a relationship to the source of light.

Texture Gradient: close objects are perceived as having rougher

textures.


Figure 4.18 Shadowing as a Cue for Depth. Shadowing makes the circle on the right look three-dimensional.


Depth Perception

Binocular Cues: cues that can be perceived by both eyes. Retinal disparity:

The difference between projected images (e.g. different angles).

Closer objects have greater retinal disparity. Convergence:

Causes feelings of tension in the eye muscles and provides another binocular cue for depth.


Perceptual Constancies

Size constancy: Allows us to perceive objects to be the same size even when

viewed from different distances. Experiences teach us about perspective.

Color constancy: The tendency to perceive objects as retaining their color even

though lighting conditions may alter their appearance. Brightness constancy:

similar to color constancy. Shape constancy:

The tendency to perceive objects as maintaining their shape, even if we look at them from different angles so that the shape of their image on the retina changes dramatically.


Figure 4.19 Brightness Constancy. The orange squares within the blue squares are the same hue, yet the orange within the dark blue square is perceived as brighter. Why?


Figure 4.20 Shape Constancy. When closed, this door is a rectangle. When open, the retinal image is trapezoidal. But because of shape constancy, we still perceive it as rectangular.


FEATURES: A CLOSER LOOK: Visual Illusions: Is Seeing

Believing? The Hering-Helmholtz and Muller-Lyer

illusions work because of our life experience.

Lifelong use of perceptual cues. Experience with perspectives.

The Ponzo illusions seems to work because of size constancy.


Figure 4.21 The Hering–Helmholtz and Müller–Lyer Illusions. In the Hering–Helmholtz illusion, are the horizontal lines straight or curved? In the Müller–Lyer illusion, are the vertical lines equal in length?


Figure 4.22 A Monstrous Illusion. The two monsters in this drawing are exactly the same height and width. Yet the top one appears to be much larger. Can you use the principle of size constancy to explain why?


Hearing: The Ear

The ear has three parts: the outer ear, middle ear, and the inner ear. The outer ear is shaped to funnel sound

waves to the eardrum. The eardrum is a thin membrane that vibrates in

response to sound waves and thereby transmits them to the middle and inner ears.


Figure 4.26 The Human Ear. The outer ear funnels sound to the eardrum. Inside the eardrum, vibrations of the hammer, anvil, and stirrup transmit sound to the inner ear. Vibrations in the cochlea transmit the sound to the auditory nerve by way of the basilar membrane and the organ of Corti.


The Ear

The middle ear functions as an amplifier. The stirrup is attached to another vibrating membrane (the

oval window) which transmits vibrations to the cochlea. The cochlea is a snail shaped structure that contains

membranes. One of these membranes is the basilar membrane. Attached to the basilar membrane is the command post of

hearing (organ of Corti). Here there are receptor cells called hair cells. Hair cells dance in response to basilar membrane vibrations. Their movements generate neural impulses which are sent to

the brain via the auditory nerve. Auditory input is then projected onto the hearing areas of the

temporal lobes of the cerebral cortex


Locating Sounds

A sound that is louder in the right ear is perceived as coming from the right.

It is difficult to determine if the sound is directly in front of or behind you.

Both loudness and the sequence in which the sounds reach the ears provide directional cues.


Deafness

More than 1 in 10 Americans has a hearing impairment, and 1 in 100 cannot hear at all.

Two major types of deafness are conductive and sensorineural deafness. Conductive deafness:

stems from damage to the structures of the middle ear. This is the hearing impairment often found among older

people. Sensorineural deafness:

stems from damage to the structures of the inner ear, most often the loss of hair cells, which normally do not regenerate.

Acoustic trauma: prolonged exposure to very loud noises. The ringing sensation that often follows exposure to loud noises

probably means that hair cells have been damaged.


The Chemical Senses

Smell If you did not have a sense of smell, an onion

and an apple would taste the same to you. Odors are detected by sites on receptor

neurons in the olfactory membrane high in each nostril.

The sense of smell adapts rapidly to odors such that we lose awareness of them.

Our sense of smell declines when we age => food doesn’t taste as good


The Chemical Senses

Taste Four primary taste qualities: sweet, sour, salty, and

bitter. Food flavor depends on its odor, texture, temperature as

well as taste. Taste cells are receptor neurons located on taste buds.

Humans have approximately 10,000 taste buds most of which are located on the edge and back of your tongue.

Taste cells reproduce rapidly enough to renew themselves weekly


The Skin Senses

The skin senses include touch, pressure, warmth, cold, and pain.

Touch and Pressure: information concerning not only touch, but also pressure,

temperature, and feedback from the muscles involved in movements of our hands.

The sense of pressure, like the sense of touch undergoes rapid adaptation.

Temperature The receptors for temperature are neurons located just

beneath the skin. Sensations of temperature are relative to skin

temperature.


Kinesthesis and the Vestibular Sense

Kinesthesis: the sense that informs you about the position and

motion of parts of the body. Sensory information is fed back to the brain from

sensory organs in the joints, tendons, and muscles.

The Vestibular Sense Your vestibular sense tells you whether you are

upright => sense of balance Sensory organs located in the ears monitor your body’s

motion and position in relation to gravity. They tell you if you are falling and if your body is changing

speed.


Extrasensory Perception

Hard research does not support the existence of ESP. Nonetheless 60% of Americans believe that

some people have psychic powers or ESP.


LIFE CONNECTIONS: Pain, Pain, Go Away-Don’t Come Again

Another Day

A Gallup survey of 2,002 adults in the U.S. showed that 89% experience pain at least once a month.

Pain means that something is wrong in the body. Pain is adaptive. There are no nerve endings for pain in the brain. Postaglandins (substance P) facilitate transmission of

the pain message to the brain and heighten circulation to the injured area.

Other aspects influence pain: Visual and other sensory inputs tell us what is happening and

influence the cognitive interpretation of the situation.


Figure 4.28 Perception of Pain. Pain originates at the point of contact, and the pain message to the brain is initiated by the release of prostaglandins, bradykinin, and substance P.


LIFE CONNECTIONS: Pain, Pain, Go Away-Don’t Come Again Another

Day.

Phantom Limb Pain. About 2 out of 3 combat veterans with amputated limbs

report feeling pain in missing or phantom limbs. Seems to involve activation of nerves in the stump of the

missing limb. Gate Theory.

The nervous system can process only a limited amount of stimulation at a time.

In a sense, there is competition for the attention of neurons.

Acupuncture. Research has shown that acupuncture stimulates

nerves that reach the hypothalamus and may also result in the release of endorphins.


LIFE CONNECTIONS: Pain, Pain, Go Away-Don’t Come Again Another

Day

Modern Psychological Methods for Coping with Pain. The primary treatment has been chemical; pain-killing

drugs. Knowledge of medical procedures reduces stress by

helping people maintain control over their situation. Distraction and Fantasy:

Diverting attention from pain helps many cope with it. Rub the injured area (for small injuries).

Hypnosis has been used to reduce chronic pain, as an anesthetic in dentistry, childbirth, even in some forms of surgery.

Exit Table of Contents Chapter 4 Sensation and Perception.

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sensory stimulation

eye rods

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