AP Psychology: Chapter 3: Sensation and Perception

An Overview of the Nervous System

• The nervous system is a complex network of cells that carries information to and from all parts of the body

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Neurons and Nerves: Building the Network

• The brain is made up of two types of cells, neurons, and glial cells
• Neurons have dendrite, which receive input, a soma or cell body, and axons that carry the neural message to other cells
• Glial cells separate, support, and insulate the neurons from each other and make up 90 percent of the brain
• Myelin insulates and protects the axons of neurons that travel in the body. These axons bundle together in " cables " called nerves. Myelin also speeds up the neural message
• Neurons in the peripheral nervous system are also coated with neurilemma, which allows the nerves to repair themselves
• A neuron contains charged particles called ions. When at rest, the neuron is negatively charged on the inside and positively charged on the outside. When stimulated, this reverses the charge by allowing positive sodium ions to enter the cell. This is the action potential Neurons fire in an all-or-nothing manner. It is the speed and number of neurons firing that tell researchers the strength of the stimulus
• Synaptic vesicles in the end of the axon terminal release neurotransmitter chemicals into the synapse, or gap, between one cell and the next. The neurotransmitter molecules fit into receptor sites on the next cell, stimulating or inhibiting that cell's firing. Neurotransmitters may be either excitatory or inhibitory
• The first known neurotransmitter was acetylcholine. It stimulates muscles, is involved in arousal and attention , and helps in memory formation. Curare is a poison that blocks its effect
• GABA is the major inhibitory neurotransmitter; high amounts of GABA are released when drinking alcohol
• Serotonin is associated with sleep , mood , and appetite
• Dopamine is associated with Parkinson's disease and schizophrenia
• Endorphins are neural regulators that control our pain response Most neurotransmitters are taken back into the synaptic vesicles in a process called reuptake
• Acetylcholine is cleared out of the synapse by enzymes that break up the molecules

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The Central Nervous System- The “Central Processing Unit”

• The central nervous system consists of the brain and the spinal cord
• The spinal cord serves two functions. The outer part of the cord transmits messages to and from the brain, whereas the inner part controls lifesaving reflexes such as the pain response
• Spinal cord reflexes involve afferent neurons, interneurons, and efferent neurons, forming a simple reflex arc
• Great strides are being made in spinal cord repair and the growth of new neurons in the central nervous system

Psychology in the News: Stem Cells: New Hope for Damaged Brains?

• Research suggests that stem cells can be obtained from adult bone marrow, making the repair and replacement of damaged neurons more feasible

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The Peripheral Nervous System- Nerves on the Edge

• The peripheral nervous system is all the neurons and nerves that are not part of the brain and spinal cord and that extend throughout the body
• There are two systems within the peripheral nervous system, the somatic nervous system, and the autonomic nervous system
• The somatic nervous system contains the sensory pathway, or neurons carrying messages to the central nervous system, and the motor pathway, or neurons carrying messages from the central nervous system to the voluntary muscles
• The autonomic nervous system consists of the parasympathetic division and the sympathetic division. The sympathetic division is our fight-or-flight system, reacting to stress, whereas the parasympathetic division restores and maintains normal day-to-day functioning of the organs

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Peeking Inside the Brain

• We can study the brain by using deep lesioning to destroy certain areas of the brain in laboratory animals or by electrically stimulating those areas ( ESB )
• We can use case studies of human brain damage to learn about the brain's functions but cannot easily generalize from one case to another
• The EEG allows researchers to measure the electrical activity of the surface of the brain through the use of electrodes placed on the scalp
• CT scans are computer-aided X - rays of the brain and show a great deal of brain structure
• MRI scans use a magnetic field and a computer to give researchers an even more detailed look at the structure of the brain. A related technique , fMRI, allows researchers to look at the activity of the brain
• PET scans use a radioactive sugar injected into the bloodstream to track the activity of brain cells, which is enhanced and color-coded by a computer

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From the Bottom Up: The Structures of the Brain

• The medulla is at the very bottom of the brain and top of the spinal column. It controls life-sustaining functions such as breathing and swallowing. The nerves from each side of the body also cross over in this structure to opposite sides

• The pons is above the medulla and acts as a bridge between the lower part of the brain and the upper part. It influences sleep, dreaming, arousal, and coordination of movement on the left and right sides of the body

• The reticular formation runs through the medulla and the pons and controls our wakefulness and arousal

• The cerebellum is found at the base and back of the brain and coordinates fine, rapid motor movement, learned reflexes, posture, and muscle tone

• The thalamus is the relay station that sends sensory information to the proper areas of the cortex

• The hypothalamus controls hunger, thirst, sleep, sexual behavior, sleeping and waking, and emotions. It also controls the pituitary gland. The limbic system consists of the thalamus, hypothalamus, hippocampus, amygdala, and the fornix

• The hippocampus is the part of the brain responsible for storing memories and remembering the locations of objects

• The amygdala controls our fear responses and memory of fearful stimuli

• The cortex is the outer covering of the cerebrum and consists of a tightly packed layer of neurons about one-tenth of an inch in thickness. Its wrinkles, or corticalization, allow for the greater cortical area and are associated with greater intelligence

• The cortex is divided into two cerebral hemispheres connected by a thick band of neural fibers called the callosum corpus

• The occipital lobes at the back and base of each hemisphere process vision and contain the primary visual cortex

• The parietal lobes at the top and back of the cortex contain the somatosensory area, which processes our sense of touch, temperature, and body position. Taste is also processed in this lobe

• The temporal lobes contain the primary auditory area and are also involved in understanding language

• The frontal lobes contain the motor cortex, which controls the voluntary muscles, and are also where all the higher mental functions occur, such as planning, language, and complex decision making

• Association areas of the cortex are found in all the lobes but particularly in the frontal lobes. These areas help people make sense of the information they receive from the lower areas of the brain

• An area called Broca's area in the left frontal lobe is responsible for producing fluent, understandable speech. If damaged, the person has Broca's aphasia in which words will be halting and pronounced incorrectly

• An area called Wernicke's area in the left temporal lobe is responsible for the understanding of language. If damaged, the person has Wernicke's aphasia in which speech is fluent but nonsensical. The wrong words are used

  Classic Studies in Psychology: Through the Looking Glass: Spatial Neglect Spatial

• Neglect comes from damage to the association areas on one side of the cortex, usually the right side. A person with this condition will ignore information from the opposite side of the body or the opposite visual field

• Studies with split-brain patients, in which the corpus callosum has been severed to correct epilepsy, reveal that the left side of the brain seems to control language, writing, logical thought, analysis, and mathematical abilities. The left side also processes information sequentially

• The right side of the brain processes information globally and controls emotional expression, spatial perception, recognition of faces, patterns, melodies, and emotions

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The Chemical Connection: The Endocrine Glands

• Endocrine glands secrete chemicals called hormones directly into the bloodstream, influencing the activity of the muscles and organs
• The pituitary gland is found in the brain just below the hypothalamus. It has two parts, the anterior and the posterior. It controls the levels of salt and water in the system and, in women, the onset of labor and lactation, as well as secreting growth hormone and influencing the activity of the other glands
• The pineal gland is also located in the brain. It secretes melatonin, a hormone that influences the sleep-wake cycle in humans and some animals in response to changes in light
• The thyroid gland is located inside the neck. It controls metabolism ( the burning of energy ) by secreting thyroxin
• The pancreas controls the level of sugar in the blood by secreting insulin and glucagons. Too much insulin produces hypoglycemia, whereas too little causes diabetes
• The gonads are the ovaries in women and testes in men. They secrete hormones to regulate sexual growth, activity, and reproduction
• The adrenal glands, one on top of each kidney, control the stress reaction through the adrenal medulla's secretion of epinephrine and norepinephrine. The adrenal cortex secretes over 30 different corticoids (hormones) controlling salt intake, stress, and sexual development

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Vocab:

• Synesthesia: disorder in which the signals from the various sensory organs are processed in the wrong cortical areas, resulting in the sensory information being interpreted as more than one sensation
• Sensation: the process that occurs when special receptors in the sense organs are activated, allowing various forms of outside stimuli to become neural signals in the brain
• Transduction: the process of converting outside stimuli, such as light, into neural activity
• Just noticeable difference (jnd or the difference threshold): the smallest difference between two stimuli that is detectable 50 percent of the time
• Absolute threshold: the lowest level of stimulation that a person can consciously detect 50 percent of the time the stimulation is present

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Examples of Absolute Thresholds

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• Pinna: the visible part of the ear

• Auditory canal: a short tunnel that runs from the pinna to the eardrum

• Visual accommodation: the change in the thickness of the lens as the eye focuses on objects that are far away or close

• Rods: visual sensory receptors found at the back of the retina, responsible for noncolor sensitivity to low

• Levels of light cones: visual sensory receptors found at the back of the retina, responsible for color vision and sharpness of vision

• Blind spot: area in the retina where the axons of the three layers of retinal cells exit the eye to form the optic nerve, insensitive to light

• Light adaptation: the recovery of the eye's sensitivity to visual stimuli in light after exposure to darkness

• Trichromatic theory: theory of color vision that proposes three types of cones: 10 red, blue, and green

• Afterimages: images that occur when a visual sensation persists for a brief time even after the original stimulus is removed

• Opponent-process theory: theory of color vision that proposes four primary colors with cones arranged in pairs: red and green, blue and yellow

• Dark adaptation: the recovery of the eye's sensitivity to visual stimuli in darkness after exposure to bright lights

• Hertz ( Hz ): cycles or waves per second , a measurement of frequency

• Habituation: tendency of the brain to stop attending to constant, unchanging information sensory

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

  • 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

• Olfaction (olfactory sense): the sensation of smell

• Gustation: the sensation of a taste

• Pitch: psychological experience of sound that corresponds to the frequency of the sound waves; higher frequencies are perceived as higher pitches

• Place theory: theory of pitch that states that different pitches are experienced by the stimulation of hair cells in different locations on the organ of Corti

• Frequency theory: theory of pitch that states that pitch is related to the speed of vibrations in the basilar membrane

• Volley principle: theory of pitch that states that frequencies from about 400 Hz to 4000 Hz cause the hair cells ( auditory neurons ) to fire in a volley pattern, or take turns in firing

• Olfactory bulbs: areas of the brain located just above the sinus cavity and just below the frontal lobes that receive information from the olfactory receptor cells

• Somesthetic senses: the body senses consisting of the skin senses, the kinesthetic sense, and the vestibular senses

• Skin senses: the sensations of touch, pressure, temperature, and pain

• Kinesthetic sense: sense of the location of body parts in relation to the ground and each other

• Vestibular senses: the sensations of movement, balance, and 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, resulting in dizziness, nausea, and other physical discomfort

• Cochlea: snail-shaped structure of the inner ear that is filled with fluid

• Auditory nerve: bundle of axons from the hair cells in the inner ear

  

• Perception: the method by which the sensations experienced at any given moment are interpreted and organized in some meaningful fashion

• Müller-Lyer Illusion: illusion of line length that is distorted by inward - turning or outward- turning corners on the ends of the lines, causing lines of equal length to appear to be different.

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

• Parapsychology: the study of ESP , ghosts, and other subjects that do not normally fall into the realm of ordinary psychology

• Perceptual set (perceptual expectancy): the tendency to perceive things a certain way because previous experiences or expectations influence those perceptions

• Top-down processing: the use of pre-existing knowledge to organize individual features into a unified whole

• Bottom-up processing: the analysis of the smaller features to build up to a complete perception

• 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

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

• Motion parallax: the perception of motion of objects in which close objects appear to move more quickly than objects that are farther away

• Accommodation: as a monocular clue, the brain's use of information about the changing thickness of the lens of the eye in response to looking at objects that are close or far away

• Continuity: the tendency to perceive things as simply as possible with a continuous pattern rather than with a complex, broken-up pattern

• Contiguity: the 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 (pictorial depth cues): cues for perceiving depth based on one eye only -binocular cues: cues for perceiving depth based on both eyes -Linear perspective: the tendency for parallel lines to appear to converge on each other

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

• Overlap (interposition): 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

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

• Figure-ground: the tendency to perceive objects, or figures, as existing on a background

• Reversible figures: visual illusions in which the figure and ground can be reversed

• Proximity: the tendency to perceive objects that are close to each other as part of the same grouping

• Similarity: the tendency to perceive things that look similar to each other as being part of the same group

• Closure: the tendency to complete figures that are incomplete

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