Chapter 3: Sensation and Perception: How the World Enters the Mind
I.
Sensing and Selecting: Opening Up to the World
A. Sensation and perception
1. Sensation is the immediate experience of basic properties of an object or event that occurs when a
receptor is stimulated.
2. Perception is the act of organizing and interpreting sensory input as signaling a
particular object of event.
3. There are three levels of processing involved in the sensory and perceptual processes.
a. Early processing, which is the registering of sensation when receptors are physically stimulated
b. Intermediate processing, which is when the sensory information is organized into coherent units
c. Late processing, which is when your perceptual processes interprets the meaning of these units.
4. Processing may be initiated by one of two ways:
a. Bottom-up processing which is initiated by stimulus input
b. Top-down processing which is initiated by knowledge, expectation, or belief
B. Psychophysics is the study of the relation between physical events and the corresponding experience of
those events. It was founded by Gustav Fechner.
1. A threshold is the point at which stimulation is strong enough to be noticed.
2. Just-noticeable difference (JND) is the size of the difference in a stimulus property needed for the
observer to notice a change has occurred.
3. Difference threshold is the difference needed to notice a stimulus change half the time.
4. Weber’s law states a constant percentage of a magnitude of change is necessary to detect a difference.
5. An absolute threshold is the smallest amount of a stimulus needed to detect that a stimulus is present.
6. Signal detection theory uses two key concepts to explain why people detect signals in some situations
but miss them in others.
a. Sensitivity, which is the threshold level for distinguishing between a signal and noise.
b. Bias, which is a person’s inclination, or willingness, to report noticing a stimulus.
C. Attention is the act of focusing on particular information, thereby processing it more fully than information
that is not attended to.
1. Selective Attention is the process of picking out a particular quality, object, or
event for relatively detailed analysis.
2. Vigilance type of attention that occurs when you are anticipating and watching for a particular event.
3. Some stimuli are sufficiently different from the ones around them that they pop out from the
surrounding stimuli and are immediately evident to us.
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II. Vision
A. Light waves have two physical characteristics that determine how our nervous system responds to them.
1. Amplitude, which is the height of light or pressure waves and is registered as brightness with light
waves and as volume with sound waves.
2. Frequency, which is the rate at which wave peaks arrive and determines color with light waves and
pitch with sound waves. Wavelength is the distance between peaks of light or sound waves.
B. The eye is the organ that converts electromagnetic light energy into nerve impulses
through a process called transduction.
1. The pupil is the opening in the eye through which light passes.
2. The iris is the circular muscle that adjusts the size of the pupil.
3. The cornea is the transparent covering over the eye, which serves to focus light to the back of the eye.
4. The lens is the flexible disk behind the cornea and pupil that focuses light onto the back of the eye
through a process called accommodation.
5. The retina is a sheet of tissue at the back of the eye containing cells that convert
light into neural impulses.
a. Rods are very light sensitive but register only shades of gray, not color.
b. Cones are less sensitive but respond most strongly to one of three wavelengths (yellow, green, or
violet) thus playing a key role in color vision.
c. There is a third, but not yet identified receptor cell in the eye, perhaps in the retina, that helps
control circadian behavior patterns.
6. The fovea is small central region of the retina with highest density of cones and the highest resolution.
7. The eye becomes more sensitive to light when you enter a darkened room or it
becomes dark outside through a process called dark adaptation.
8. The optic nerve is a large bundle of nerve fibers carrying impulses from the retina into the brain.
9. Theories of color vision.
a. Trichromatic theory was pioneered by Hermann Von Helmholtz and Thomas Young in the 19th
century. It argues that color vision arises from combinations of neural impulses from three kinds of
sensors, each of which responds maximally to a different wavelength.
b. The opponent process theory was developed by Ewald Hering at the turn of the 20th century.
(1) Argues cells for color vision organized into 3 pairs: red-green, blue-yellow, and black-white.
(2) Stimulation of one color of a pair will inhibit the other.
c. Both theories are supported by research.
(1) Scientists have found that there are cones that are particularly sensitive to three different
frequencies of light: yellow, green, and violet. This supports the trichromatic theory.
(2) Phenomena such as afterimage effect and color blindness, support opponent process theory.
d. Colors vary in three different ways: hue, saturation, and brightness.
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C. Visual perception: Principles of perceptual organization
1. Figure/ground refers to tendency to lock into a figure as the object of interest by distinguishing it from
the background. Camouflage makes it difficult by making the figure blend into the background.
2. There 5 Gestalt laws of organization.
(a) Proximity: objects that are near each other tend to be grouped together.
(b) Good continuation: marks that fall along smooth curve or straight line tend to be grouped together.
(c) Similarity: objects that look alike tend to be grouped together.
(d) Closure: we tend to close any gaps in a figure and see a complete figure.
(e) Good form: marks that form a single shape tend to be grouped together.
3. Depth perception cues
(a) Binocular cues require the use of both eyes working together to judge distance.
(1) Retinal (binocular) disparity uses stereopsis to register depth-objects to about 10 feet away.
(2) Motion cues judge distance based on object’s movement as in the case of motion parallax.
(b) Monocular static cues judge distance with only one eye without the movement of the eye.
(1) Texture gradient is a progressive change in the texture of an object that signals distance.
(2) Linear perspective involves making parts of objects farther away actually smaller on the page.
(3) An occlusion cue results when one object partially covers another.
4. Perceptual constancies occur when an object or quality looks the same even though the sensory
information striking the eyes changes.
(a) Size constancy involves seeing an object as being the same when viewed at different distances and
visual angles.
(b) Shape constancy involves seeing objects as having the same shape even when the image on the
retina changes.
(c) Brightness and color constancy involve seeing objects as having the same lightness, brightness,
or color in different viewing conditions.
D. Recognizing and identifying objects
1. People often use beliefs and expectations as a context for forming perceptual expectancies, which can
affect how they perceive or interpret a situation.
2. Blindsight occurs when people who have suffered strokes that leave them blind are still able to “know”
when spots of light are present, even where they are, although they have no conscious awareness of
seeing the lights.
3. Generally, people only perceive with high accuracy events to which they are paying close attention.
4. Repetition blindness - inability to see second occurrence of stimulus that appears twice in succession.
5. Attentional blink is a rebound period in which a person cannot pay attention to one thing after having
just paid attention to another.
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III. Hearing
A. Early audition
1. 40% of normal people emit a detectable soft humming sound from their ears.
2. Sound waves
a. Pitch is how high a sound seems - higher frequencies experienced as higher pitches.
b. Volume is strength of a sound -pressure waves with greater amplitude produce louder sound.
3. The ear has three parts:
a. The outer ear, which includes the pinna, the auditory canal, and the tympanic membrane.
b. The middle ear, which includes the three small bones (the hammer, anvil, and stirrup) that transmit
vibrations from the tympanic membrane, the oval window and the round window.
c. The inner ear, which contains the semicircular canals, the cochlea, and the auditory nerve.
(1) The basilar membrane, inside the cochlea, is where different sound frequencies are coded into
neural impulses when hair cells along the basilar membrane are moved.
4. There are two main theories about the way the basilar membrane converts pressure waves into
perceived sound:
a. Frequency theory argues that higher frequencies produce higher rates of neural firing.
b. Place theory argues that different frequencies activate different places along the basilar membrane.
c. Researchers have found that part of the primary auditory cortex is arranged so
that higher and lower sounds are coded in different areas, in an arrangement called tonotopic
organization.
5. Deafness can occur for many reasons.
a. Nerve deafness occurs when the hair cells are destroyed by loud sounds.
b. Conduction deafness is caused by a physical impairment of the outer or middle ear.
B. Intermediate audition
1. We organize sound into meaningful units according to auditory scene analysis.
a. To do this for spoken language, we must overcome the speech segmentation problem.
b. We use categorical perception, in which we identify sounds as belonging to
distinct categories that correspond to basic units of speech.
2. We use two types of cues to locate sounds. Some use only one ear, while others use both ears.
C. Late audition
1. Our brain often invokes a process called phonemic restoration to fill in missing words or parts of words
in a communication.
2. In the cocktail party phenomenon, you may be tracking a conversation without being aware of it until
you hear your name mentioned, and then you are suddenly aware of the conversation.
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IV. Sensing in Other Ways
A. Smell
1. Taste and smell are often grouped together as the chemical senses.
2. People differ widely in their sense of smell, or olfaction:
a. Some people are 20 times more sensitive to odors than others.
b. Women are generally better than men at detecting many types of odors.
c. Younger adults are generally better at detecting odors than either children or
middle-aged adults
3. The best theory of odor detection relies on a “lock and key” metaphor, with molecules being like keys,
and olfactory receptors being like locks. The overall pattern of which receptors are stimulated helps us
determine a particular odor.
3. Two major neural tracks leave the olfactory bulb one linked to memory and the other to brain centers
involved in emotional responses.
B. Taste
1. Taste buds are microscopic structures mostly on the bumps on the tongue’s surface, but also on the
cheeks and back of the throat.
a. They are replaced about once every ten days.
b. All kinds of taste buds are found in most locations of the tongue.
2. The taste of all foods is made up of a combination of four specific tastes: sweet, sour, salty, and bitter.
3. Some free nerve endings in our mouth are irritated by spicy foods.
4. A food’s flavor is dependent on both taste and smell.
C. Somasthetic senses are involved in perception of one’s body and its position in space.
1. The kinesthetic sense registers the movement and position of the limbs.
2. The vestibular sense provides information about the body’s orientation relative to gravity.
3. The sense of touch depends on the actions of millions of different receptors in our skin.
a. The skin is the body’s largest organ.
b. In general, women are more sensitive to touch than are men.
4. Our sense of temperature is based on separate receptors in the skin for hot or for cold. Paradoxical
cold occurs when nerve stimulation by something hot produces the sensation of cold.
5. Our sensation of pain arises from a number of different factors.
a. Double pain occurs when an injury first causes sharp pain and later dull pain, due to the action of
two different fibers sending messages at different speeds.
b. Endorphins are painkilling chemicals produced naturally in the brain.
c. The gate control theory of pain involves the top-down inhibition of interneurons that regulate the
input of pain signals to the brain.
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3. Extra sensory perception is the supposed ability to perceive and know things
Without using the ordinary senses.
a. Telepathy is the ability to send or receive thoughts directly, mind to mind.
b. Clairvoyance is the ability to know about events directly.
c. Precognition is the ability to foretell future events.
d. Psychokinesis is the ability to move or directly affect physical objects with your mind.
e. While there is some research that suggests some ESP effects, psychologists are generally skeptical
because:
(1) The effects are difficult to replicate.
(2) It is not known how the brain could send or receive ESP signals.
(3) It is not known what form ESP signals might take.
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