Chapter 4

CHAPTER FOUR: SENSATION AND PERCEPTION

LO 4.1: Describe basic principles of sensation and perception.

LO 4.2:Explain how the visual system enables us to see and, by communicating with the brain, to perceive the world.

LO 4.3:Understand how the auditory system registers sound and how it connects with the brain to perceive it.

LO 4.4:Explain how the skin, chemical, kinesthetic, and vestibular senses work.

LO 4.5:Identify the everyday practices associated with protecting vision and hearing.

  1. Chapter Overview
  2. Chapter Features
  3. Connections
  4. Teaching the Chapter
  1. Lecture Outlines by Section
  2. Suggested Activities
  1. Critical Thinking Questions
  2. Polling Questions
  3. Apply Your Knowledge
  4. Suggested Readings and Media
  5. Activity Handouts
  6. Answer Key to Activity Handouts

Chapter Overview

Experiencing Psychology: Our Senses: The world’s greatest smellers and the world’s worst smell

  • The sense of smell is critical for survival of many animals.
  • Generally, people don’t think about who the “World’s Greatest Smeller” is. But, we do often consider our perceptions of what we think might be the worst or best smells around.
  1. How We Sense and Perceive the World
  2. The Processes and Purposes of Sensation and Perception
  • Sensation occurs when a person receives stimulus energy from the external environment.
  • The process of transferring physical energy into electrochemical energy is called transduction.
  • Perception occurs when a person organizes and interprets sensory information in order to give it meaning.
  • Sensation and perception are two separate processes that go hand in hand. Sensation can be considered the raw materials of experience, while perception is the experience itself!
  1. Bottom-Up and Top-Down Processing
  1. Bottom-up processing occurs when the information from the external environment is registered and sent up to the brain for interpretation. Bottom-up processing occurs with first-time information, meaning information that a person is not familiar with.
  2. Top-down processing occurs with higher levels of cognitive processing, starting with the cognitive processes in the brain. Top-down processing occurs with information that a person is already familiar with.
  3. Listening to a song is a great way to understand bottom-up and top-down processing.
  1. Psychological Inquiry: Old Woman or Young Woman?
  2. The Purposes of Sensation and Perception
  1. The purpose of perception is to take information from the outside world and represent it internally.
  2. From an evolutionary perspective, the purpose of perception is to adapt to stimuli in order to survive. Take, for example, sharks; they have a keen sense of smell that can detect drops of blood in the water.
  1. Sensory Receptors and the Brain
  1. Sensory receptors are cells that detect and transmit information to sensory nerves in the brain.
  2. Sensory receptors set off action potentials in sensory neurons, which then carry the information to the central nervous system.
  3. The sense organs and sensory receptors have three classes based on the type of energy that is being transmitted. The first is photoreception, which involves the detection of light. Next is mechanoreception, which is the detection of pressure, vibrations, and movement perceived as touch, hearing, and equilibrium. The third class is chemoreception, which is the detection of chemical stimuli that is detected as smell and taste.
  4. On rare occasions senses can become “confused.” Synaesthesia refers to an experience in which one sense induces an experience in another sense. For example, a person might “see” music.
  5. Phantom limb pain is another case in which senses become “confused.” Individuals who have lost limbs report “feeling” pain in the limb that no longer exists. Research on mirror therapy has mixed results in treating phantom leg syndrome.
  6. Extrasensory perception ESP means that someone can detect information from the world without receiving any concrete sensory input. An example of ESP is telepathy the ability to read a person’s mind. There are many reasons to consider ESP questionable.
  7. Critical Controversy: Can We Feel the Future?
  8. Is it possible that future events can predict current behavior? Several studies were conducted by Daryl Bem which caused much controversy over the topic of ESP and precognition. The statistics which Bem used are at the heart of the controversy. This highlights some of the tension within science between openness of ideas and intense skepticism.
  1. Thresholds
  • Psychophysics is the study of linking the physical properties of stimuli with a person’s experience of them.
  1. Absolute Thresholds
  1. An absolute threshold is the minimum amount of energy needed for a person to detect something. If a stimulus falls below the threshold, then a person does not experience it.
  2. Under ideal circumstances, a person’s absolute thresholds are very low. The problem is that there is so much noise around people that they cannot detect half of the stimuli that are confronting them. Noise is the term given to irrelevant and competing stimuli.
  1. Difference Threshold
  1. Difference threshold refers to the difference that must exist between two stimuli before the difference is detected.
  2. The difference threshold is also referred to as the just noticeable difference.
  3. Difference thresholds increase as a stimulus becomes stronger; at low very levels of stimulation, a small change can be detected; but a very high levels, small changes are less likely to be detected.
  4. Weber’s law is the idea that two stimuli must differ by a constant minimum percentage, rather than a constant amount, to be perceived as different.
  1. Subliminal Perception

a.Subliminal perception is when people are affected by information that is presented below their level of awareness.

  1. Psychological Inquiry: Subliminal Perception: Working Up a Thirst
  1. Signal Detection Theory
  1. Signal detection theory focuses on decision making about stimuli while in the presence of uncertainty. It depends on the individual and contextual variations such as fatigue, expectancy, and the urgency of the moment.
  2. Information acquisition refers to the information that is produced in a brain scan.
  3. Criterion is the basis for making a decision about the available information.
  4. In signal detection theory, there are four possible outcomes: Hit, Miss, False Alarm, and Correct Rejection.
  1. Perceiving Sensory Stimuli
  2. Attention
  3. Selective attention involves focusing in on a specific aspect of an experience while ignoring the others.
  1. Attention is not only selective, but is also shiftable, meaning that a person can be focusing attention on one thing, but then switchattention to something else.
  2. The Stroop effect is an example of automatic attention. A person attempts to name the colors in which words are presented, but the words do not state the color of the meaning of the word. For example, the wordred would be written in the color orange. A person would have difficulty stating “orange” when the word is red.
  1. Perceptual Set
  1. A perceptual set is the predisposition to perceive something in a particular way.
  1. Sensory Adaptation
  2. Sensory adaptation occurs when there is a change in the responsiveness of the sensory system based on the average level of surrounding stimulation.
  3. An example of sensory adaptation is when a person first jumps into a swimming pool. The water is cold and shocking, but after being in the water for a few minutes, the person adapts to the temperature of the water.
  1. The Visual System
  1. The Visual Stimulus and the Eye
  2. Light
  1. Light is a form of electromagnetic energy. Light travels through space in waves.
  2. The wavelength of light is the distance from the peak of one wave to the peak of the next.
  3. Amplitude is the height of the wave and it is associated with the brightness of a visual stimulus.
  4. Purity is the mixture of wavelengths in light.
  1. The Structure of the Eye
  1. The eye is set up like a camera in that it gets the picture of the world.
  2. Getting the Best Picture of the World
  3. The sclera is the white outer part of the eye that gives the eye its shape and protects the eye from injury.
  4. The iris is the colored part of the eye.
  5. The pupil, which appears black, is the opening in the center of the iris. The iris contains muscles that allow the pupil to get larger or smaller depending on how much light is being let into the eye.
  6. The cornea is the clear membrane on the outer part of the eye. The curved surface on the cornea bends light on the surface of the eye in order to focus it to the back of the eye.
  7. The lens is transparent and somewhat flexible. When a person is looking at an object far away, the lens has a relatively flat shape. However, when a person is looking at an object that is closer, more bending of the light is needed.
  1. Recording Images on the Retina
  2. The retina is the light-sensitive surface that records what a person sees and then converts it to a neural impulse for processing in the brain.
  3. The retina is the most important mechanism for sight.
  4. Rods are sensitive to light and allow a person to see at night.
  5. Cones are used for color perception and are not very helpful at night.
  6. The fovea is in the center of the retina. It contains only cones and is important to many visual tasks.
  7. Rods and cones transduce light into electrochemical impulses that go to the bipolar cells and then move on to ganglion cells. The axons of the ganglion cells make up the optic nerve.
  8. The blind spot on the retina contains neither rods nor cones.
  1. Visual Processing in the Brain
  • The optic nerve leaves the eye and carries information about light to the brain.
  • Stimuli in the left visual field travel to the right side of the brain, and vice versa.
  • The optic chiasm is where the nerve fibers divide and visual information crosses over to the opposite side of the brain.
  1. The Visual Cortex
  1. The visual cortex is located in the occipital lobe of the brain. It functions in vision.
  2. Feature detectors are neurons or groups of neurons in the brain’s visual system, and they respond to particular features of a stimulus.
  1. Parallel Processing
  1. “What” and “where” are two questions that need to be answered in order for people to respond appropriately to a visual stimulus.
  2. The “what” pathway is in the temporal lobe and processes information about what the object is. The “where” pathway is located in the parietal lobe and processes information about an object’s location.
  3. Parallel processing is a simultaneous distribution of information across different neural pathways. It helps information move rapidly through the brain.
  1. Binding
  2. Binding is when the different pathways and cells bring together and integrate information.
  3. Through binding a person can integrate information about various parts of an object. For example, if a person sees a chair, then through binding he not only sees just the chair, but he also sees the size, the color, the motion, etc., of the chair.
  1. Color Vision
  2. Color is a pattern of neural responses that generate color vision.
  3. The trichromatic theory states that color perception is produced by three types of receptors.
  4. The term color blind refers to seeing some colors but not others. Color blindness depends on which of three kinds of cones (green, red, and blue) is not working.
  5. The opponent-process theory states that cells in the visual system respond to red-green and blue-yellow colors. A cell excited by red and green could be inhibited, or a cell excited by blue and the yellow could be inhibited.
  1. Perceiving Shape, Depth, Motion, and Constancy
  • To perceive a visual stimulus, the fragments of information that the eye sends to the visual cortex must be organized and interpreted.
  • The figure-ground relationship occurs when a person organizes the perceptual field into stimuli that stand out (figure) and those that are left over (ground).
  • Gestalt psychology explains how people naturally organize their perceptions according to certain patterns. Closure is a gestalt principle; when people see a disconnected or complete figure, they seea whole. Proximity is a second gestalt principle; when individuals see objects as close to each other, they tend to group them as together. The third gestalt principle issimilarity; when objects are similar, individuals tend to group them together.
  1. Depth Perception
  2. Depth perception is the ability to see objects in three dimensions.
  3. Binocular cues are depth cues that depend on the combination of the images in the left and right eyes and on the way the two eyes work together. For example, if a person holds their hand over one eye and focuses on an object and then switches to cover their other eye, the switching back and forth between the eyes will cause the object to jump back and forth.
  4. The difference between images in the two eyes is the binocular cue of disparity which is used to determine depth. Convergence is another binocular cue.
  5. Monocular cues are depth cues that are available from the image in one eye, either the left or the right eye. Some examples of monocular cues are: familiar size, height in the field of view, linear perspective, overlap, shading, and texture gradient.
  1. Motion Perception
  2. In some animals, motion perception is a means of survival.
  3. Apparent motion occurs when an object is stationary but it is perceived as moving. An example of apparent motion is watching an IMAX movie. Two forms of apparent motion are stroboscopic motion and movement aftereffects.
  1. Perceptual Constancy
  2. Perceptual constancy refers to the recognition of objects as remaining stationary and unchanging even though sensory input about them is changing. There are three types of perceptual constancy: size constancy, shape constancy, and brightness constancy.
  1. The Auditory System
  1. The Nature of Sound and How We Experience It
  2. Sounds waves are vibrations in the air that are processed by the auditory system.
  3. Wavelength determines the frequency of the sound wave or the number of cycles that pass through a point in a given time.
  4. Pitch is the perceptual interpretation of the frequency of a sound. High-frequency sounds are perceived as having high pitch, such as with a soprano voice. Likewise, low-frequency sounds have a low pitch, such as with a bass voice.
  5. Amplitude is measured in decibels and is the amount of pressure produced by sound waves relative to the standard.
  6. Loudness is the perception of sound waves amplitude.
  7. The perceptual quality of a sound is known as timbre,which is responsible for us noticing the quality differences in human voices.
  1. Structures and Functions of the Ear
  2. The ear transmits a high-fidelity version of sounds in the world to the brain for interpretation.
  1. Outer Ear
  2. The outer ear contains the pinna, which is the visible outer part of the ear. It also contains the external auditory canal.
  3. Middle Ear
  4. After passing through the pinna, sound waves go through the auditory canal to the middle ear.
  5. The eardrum vibrates in response to sound.
  6. The hammer, anvil, and stirrup are three small bones in the middle ear. When they vibrate, the sound waves are transmitted to the inner ear.
  7. Inner Ear
  1. The inner ear contains the oval window, the cochlea, and the basilar membrane.
  2. The purpose of the inner ear is to transduce sound waves into neural impulses that are then sent to the brain for interpretation.
  3. In humans and other mammals, there are hair cells that line the basilar membrane. They are the sensory receptors of the ear. Hair cells can be damaged from too much loud noise. Tinnitus is another result of damage to hair cells. With tinnitus there is ringing in a person’s ears.
  1. Theories of Hearing
  1. Place theory is when each frequency produces vibrations at a particular spot on the basilar membrane. A high-frequency sound stimulates a specific part of the basilar membrane; however, a low-frequency sound causes a large portion of the basilar membrane to be displaced.
  2. Frequency theory states that the perception of a sound’s frequency depends on how often the auditory nerve fires. High-frequency sounds cause the nerve to fire more so than low-frequency sounds.
  3. The volley principle is when a cluster of nerve cells fire neural impulses in rapid succession that produce a volley of impulses.
  1. Auditory Processing in the Brain
  2. Once information is picked up from the environment it must move on to the brain for interpretation.
  3. Information about sound moves from the hair cells of the inner ear to the auditory nerve, which then carries the neural impulses to the brain.
  1. Localizing Sound
  1. A sound coming from the left reaches the left ear faster than it reaches the right ear.
  2. The sound reaching the closer ear is more intense because it did not have to travel as far and also because the other ear is in the sound shadow of the listener’s head.
  3. Differences in the timing of the sound and the intensity of the sound help a person to locate a sound.
  1. OTHER SENSES
  1. The Skin Senses
  2. The cutaneous senses are the skin receptors on the skin for temperature, touch, and pain.
  1. Touch
  2. Processing Information About Touch
  3. With touch, a person is detecting mechanical energy, or pressure against the skin.
  4. Sensory fibers from receptors in the skin enter the spinal cord and from there the information travels to the brain stem.