Chapter Three: Sensation and Perception

Basic Concepts of Sensation  *Sensation is the process by which physical stimuli

that impinge on our sensory organs [receptors in the sense organs are activated] are converted into neural impulses that the brain uses to create our experiences of vision, touch, hearing, taste, smell, etc.  *Sensory receptors – Are specialized cells [neurons] that detect sensory stimuli and convert them into neural impulses.  Psychophysics – Is the study of how physical sources of stimulation - light, sound, odors, and etc. relate to our experience of these stimuli in the form of sensations.

Sensory Receptors  Difference threshold (just noticeable differences, jnd)-

(Ernst Weber) is the minimal difference between two stimuli that people can reliably detect.  Absolute threshold (Gustav Fechner) – Is the smallest amount of stimulation that a person can reliably detect 50% of the time.  ______ _____________ are stimuli just strong enough to activate the sensory receptors but not strong enough for people to be consciously aware of them.

Habituation and Sensory Adaptation  Habituation – Is the tendency of the brain to

stop attending to constant, unchanging information. Sensory receptors are still responding to stimuli.  *Sensory adaptation – Is the process by which sensory receptors adapts to constant stimuli by becoming less sensitive to them. Sensory receptors are no longer responding to stimuli.

Sensory Adaptation  *Through the process of sensory adaptation, receptor cells

become less sensitive to constant or unchanging stimuli.  *VISION: SEEING THE LIGHT – Vision is the process by which light energy is converted into signals (neural impulses) that the brain interprets to produce the experience of sight.  *LIGHT: THE ENERGY OF VISION – Light is _____________ energy in the form of electromagnetic radiation (electrically charged particles). Visible light occupies only a small portion of the range of electromagnetic radiation that is called the electromagnetic spectrum. To the perception of light, there are three aspects: brightness, color, and saturation. Brightness is determined by the amplitude of the wave. Color is determined by the length of the wave. Saturation refers to the purity of color we perceive.

The Eye: The Visionary Sensory Organ/Its Structure  *The _____________ is the organ with receptor cells that

respond to light. Light enters the eye through the ________, which is a transparent membrane covering the surface of the eye; it also focuses most of the light coming into the eye.  A muscle called the ___________ contracts or expands to determine the amount of light that enters. The _________ of the eye is the black opening inside the iris.  _______ _________ is the name of the process by which the lens changes its shape to focus images more clearly on the retina.  The retina, which is a light-sensitive area at the back of the eye, contains three layers: ganglion cells, bipolar cells, and photoreceptors cells that are sensitive to various light waves called __________ and _________.

Photoreceptors- Part 1  Rods and cones convert the physical energy of light

into __________ signals that the brain processes to create visual sensations.  The ______ in your eye are responsible for your peripheral vision.  The neural signals produced by the photoreceptors pass back through a layer of interconnecting cells called bipolar cells and then through a layer of neurons called_________ cells.  The ____________ nerve, which contain millions of ganglion axons, transmits visual information to the visual cortex which lies in the occipital lobes.

Photoreceptors – Part 2  What is a blind spot?  COLOR VISION – The trichromatic theory, which was

first proposed by Thomas Young and later modified by Hermann von Helmholtz, states that our ability to see different colors depends on the relative activity of three types of color receptors in the eye (red, green, and blue - one for each of the three primary colors of light).  *Afterimages – Are visual images of a stimulus that remains after the stimulus is removed. See p. 100 fig. 3.6.

Second Theory of Color Perception  *Opponent-process theory – suggests that the eyes have

three types of color receptors; however, each color receptor consists of a pair of opposing receptors. Rather than having three separate receptors for red, green, and blue, some receptors are sensitive to red or green; others to blue or yellow; and others, to black or white.  *What are trichromats?- Persons with normal color vision who can discern all the colors of the visual spectrum.  *What are monochromats?- Persons who have no color vision and can see only in black and white.  *What are dichromats?- Persons who can see some colors but not others.

Hearing – The Mechanics  We hear by sensing sound waves, which

result from changes in the ____________ of air or water. When sound waves impinge upon the ear, they cause parts of the ear to __________. These vibrations are then converted into _________________ signals that are sent to the brain.

Sound: Sensing Waves of Vibrations  Unlike light that can travel through emptiness,

sound exists only in a medium, such as air, liquids, gases, or solids. Vibrations are characterized by such physical properties as amplitude (the height of the wave, which is a measure of the amount of energy in the sound wave) and frequency (the number of complete waves, or cycles, per second). The amplitude of sound waves determines their perceived loudness and is measured in decibels.

The Ear: A Sound Machine  The outer ear (__________) funnels sound waves to

the __________, a tight membrane that vibrates in response to them. The vibrations are then transmitted through three tiny bones in the middle ear called the ____________. The vibration is then transmitted to the oval window. The oval window connects the middle ear to the ___________. The vibration inside the cochlea, causes the basilar membrane to vibrate. The basilar membrane is attached to a gelatinous structure called the organ of Corti, which is lined with hair cells that serve as auditory ______________. The message is then received by the auditory cortex, which is located in the temporal lobes of the cerebral cortex.

Perception of Pitch – Perceiving the Highs and Lows of Sound  *Place Theory – suggests that people perceive a

sound to have a certain pitch according to the place along the basilar membrane that vibrates the most when sound waves of particular frequencies strike the ear.  *Frequency Theory – the belief that pitch depends on the frequency (speed) of vibration of the basilar membrane and the volley of neural impulses transmitted to the brain via the auditory nerve.  *Volley Principle – The principle that relates the experience of pitch to the alternating firing of groups of neurons along the basilar membrane.

Protecting your hearing  *Conduction (Hearing Impairment) deafness

– Refers to a form of deafness, usually involving damage to the middle ear, in which there is a loss of conduction of sound vibrations through the ear; vibrations cannot be passed from the eardrum to the cochlea..  *Nerve deafness – Refers to deafness associated with nerve damage, usually involving damage to the hair cells or the auditory nerve itself.

Gustation: How we taste the World/The flavorful Sense  There are special kinds of neurons found in

the mouth that are responsible for the sense of taste.  Hans Henning, in 1916, proposed that there are four primary tastes: _______, sour, ______, and bitter. In 1996, Lindermann supported the idea that there is a fifth taste receptor that detects a pleasant brothy taste he called “umami”. Umami means brothy, meaty, or savory

Olfaction: What Your Nose Knows  Stimulation of the sense of smell depends on the

shape of the molecules of chemical substances. Smell is the only sense in which sensory information does not go through the thalamus on its way to the cerebral cortex. Olfactory information travels through the olfactory nerve directly to the olfactory bulb, a structure in the front of the brain above the sinus cavity and just below the frontal lobes that receive information from the olfactory receptor cells. This information is then routed to the olfactory cortex in the temporal lobe and to several structures in the limbic system.

Somesthetic Senses: What the Body Knows  THE SKIN SENSES: YOUR LARGEST SENSORY ORGAN –

Your skin contains receptors for the body’s skin senses that code for sensations of touch and pressure. The sensory receptors transmit sensory information to the spinal cord, which relays it to the somatosensory cortex, the part of the cerebral cortex that processes information making us aware of how and where we have been touched. There are three somesthetic sense systems, the skin senses, having to do with touch, pressure, ______________, and pain; the kinesthetic sense, having to do with the location of body parts in relation to the ground and to each other; and the vestibular senses, having to do with movement and body position.

Perception of Touch, Pressure, and Temperature  There are varied sensory receptors in the

skin, some of them responding to only one kind of sensation. Example, the Pacinian corpuscles are just beneath the skin and responds only to the sense of pressure.  CIPA – Congenital insensitivity to pain with anhidrosis (Is a disruption in the body’s heat/cold sensing perspiration system, so that the person is unable to cool off the body by sweating; the inability to sweat in response to heat; failure of the sweat glands.)

Gate-Control Theory of Pain  According to the gate-control theory of pain, a gating

mechanism in the spinal cord opens and closes to let pain messages through to the brain or to shut them out. The term “gate” is a pattern of nervous system activity that results in either blocking pain signals or letting them through.  Kinesthetic sense – Gives the sense of the location of body parts in relation to the ground and each other.  Vestibular sense – Gives the sensations of ________, balance, and body position. There are two kinds of vestibular organs, the otolith organs and the semicircular canals. The otolith organs are responsible for detecting linear acceleration of the head, while the semicircular canals are involved in sensing changes in the direction and movement of the head.

The Kinesthetic and Vestibular Senses: Of Grace and Balance  An explanation of motion sickness in which the

information from the eyes conflicts with the information from the vestibular senses, resulting in dizziness, nausea, and other physical discomfort is called________________.

The ABC’s of Perceiving our World: Perception vs. Reality  *Perception

is the process by which the brain interprets sensory information, turning it into meaningful representations of the external world.  The first step in perception is giving attention.  Selective attention - Is the process by which we attend to meaningful stimuli and filter out irrelevant or extraneous stimuli.

Perceptual Constancies  *Shape constancy- The tendency to perceive an object as having the same shape despite differences in the images it casts on the retina.  *Size constancy- The tendency to perceive an object as having the same size…  *Brightness constancy- The tendency to perceive objects as retaining their brightness even when they are viewed in dim light.

The Gestalt Principles/Laws of Perceptual Organization  Laws of perceptual organization identifies

principles by gestalt psychologists that describe the way in which the brain groups bits of sensory stimulation into meaningful wholes or patterns, e.g., figure – ground perception and laws of grouping.  Figure-ground perceptions- Refers to how we see figures and the background against which the figures are perceived serves as the ground. See figure 3.16, p. 117.

Laws of Grouping  Proximity – Is the principle that objects that are near    

each other will be perceived as belonging to a common set. Closure- the perceptual principle that people tend to piece together disconnected bits of information to perceive whole forms. Similarity – The principle that objects that are similar will be perceived as belonging to the same group. Continuity – The principle that a series of stimuli will be perceived as representing a unified form. Contiguity – Is the tendency to perceive two things that happen close together in time as being related.

Cues to Depth Perception  Binocular Cues for Depth- Cues for depth that involve

both eyes. Because each eye receives slightly different images of the world, the brain interprets the difference in the two retinal images as cues to the relative distances of objects.  Binocular (Retinal) disparity- Is the binocular cue for distance based on the slight differences in the visual impressions formed in both eyes.  Convergence- Refers to the degree of tension required to focus two eyes on the same object.  Monocular cues- Refer to cues for depth that can be perceived by each eye alone, such as relative size and interposition.

Perceptual Illusions: Do Your Eyes Deceive You?         

Visual illusions- Are misperceptions of visual stimuli, e.g., Muller-Lyer Illusion and Ponzo illusion, See fig. 3.27. An illusion is a perception that does not correspond to reality. Factors That Influence Perception: 1) Perceptual Sets or Perceptual Expectancy – Is a person’s tendency to perceive things a certain way because of their previous experiences or expectations influenced them. 2) Top-down processing – A mode of perceptual processing by which the brain identifies patterns as meaningful wholes rather than as piecemeal constructions. 3) Bottom-up processing – A mode of perceptual processing by which the brain recognizes meaningful patterns by piecing together bits and pieces of sensory information.

Parapsychology  Parapsychology – The study of paranormal

phenomena; not scientifically explainable.  ESP (Extrasensory perception) – Perception occurring without the benefit of the known senses.

 THE END  STUDY

STUDY

STUDY

Signal Detection  Signal-detection theory – states that the

threshold for detecting a signal depends not only on the properties of the stimulus itself, but also on the level of back ground stimulation, or noise, and on the biological and psychological characteristics of the perceiver. Levels of fatigue also contribute to signal detection; how well you are listening at this moment.