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EPPP-Physiological Psychology


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Amphetamines and Untoward Events
1. AMPHETAMINES: Block the re-uptake mechanisms at noradrenergic and dopaminergic synapses, resulting in potentiation of the transmitter's effects. Amphetamines produce
physiologically and psychologically stimulating effects. Now, they are primarily used to treat narcolepsy and hyperactivity.
2. UNTOWARD EFFECTS: Usually due to overdose (toxicity), and include nausea, vomiting, irritability, headache, palpitations, dizziness, anxiety, apprehension, confusion
and dysphoria.
3. AMPHETAMINE PSYCHOSIS: A psychotic-like reaction resembling paranoid
schizophrenia, which can result from long-term use or a very large dose of amphetamine.
Anti-Depressants and Untoward Events
1. MAOIs: Most effective for atypical depressions (e.g., those involving anxiety, increased appetite, hypochondriasis and hostility).
2. UNTOWARD EFFECTS OF MAOIs: Drowsiness, dizziness, constipation, dry mouth, orthostatic hypotension, tremor and edema. MAOIs are highly toxic and can be fatal if an overdose is taken. They must not be mixed with certain drugs or foods containing
3. TRICYCLICS: Most effective for unipolar and endogenous (non-reactive) depressions. The tricyclics include Tofranil, Sinequan and Elavil.
4. UNTOWARD EFFECTS OF TRICYCLICS: Include anticholinergic effects (see
"Neuroleptics and Untoward Effects") and cardiovascular symptoms; e.g., orthostatic hypotension, tachycardia, palpitations, hypertension (therefore, these drugs must be used with caution for individuals with heart disease). Other effects are sedation, confusion,
disorientation, insomnia, skin rashes, paresthesias, blood dyscrasias, nausea, vomiting, weight gain, changes in libido and paradoxical agitation or depression. Many of these effects are more common in elderly patients and can be alleviated by reducing dosage
evel. Because an overdose can be lethal, tricyclics should be prescribed in small quantities for patients at high risk for suicide.
ANXIOLYTICS and Untoward Events
1. ANXIOLYTICS: Used as minor tranquilizers and anti-anxiety agents. Anxiolytics include meprobamate and benzodiazepines. Benzodiazepines (e.g., Valium, Librium, Dalmane) are
the most widely-prescribed drug for anxiety and are particularly useful for treating anxiety that is severe, acute, reactive to environmental or internal stresses and accompanied by agitation, apprehension or tension.
2. UNTOWARD EFFECTS: Common side effects are drowsiness, lethargy and ataxia.
Anxiolytics promote psychological dependence, and chronic use results in tolerance and physical dependence. Meprobamate is generally associated with more severe withdrawal symptoms (and a greater risk for suicide) than the benzodiazepines.
1. APHAGIA: A lack of eating produced by destruction of the lateral hypothalamus (LHA).
2. APHASIA: (a) EXPRESSIVE APHASIA: Inability to produce (express) language
associated with damage to Broca's area. (b) RECEPTIVE APHASIA: Deficits in the
comprehension of spoken and written words produced by damage to Wernicke's area. (c) CONDUCTION APHASIA: Inability to distinguish and repeat speech sounds caused by damage to the arcuate fasciculus.
3. ATAXIA: Loss of ability to coordinate voluntary body movements associated with
pathology in the cerebellum.
4. VISUAL AGNOSIA: Inability to interpret the meaning of visual stimuli; a.k.a. "psychic blindness."
Audition Theories
1. FREQUENCY THEORY: Proposes that auditory perception is related to the frequency of nerve impulses conducted in the auditory nerve, which matches the frequency of the
stimulus, at least for tones less than 1,000 Hz.
2. PLACE THEORY: Theory of pitch perception that asserts that the perception of high frequency tones is a function of the place on the basilar membrane stimulated by the tone.
Autonomic and Somatic Nervous System
1. AUTONOMIC NERVOUS SYSTEM (ANS): The division of the peripheral nervous system
involved in the control of visceral functions (e.g., heart rate, blood pressure, respiration, digestion, and sweating). The ANS is associated primarily with involuntary movements, but research on biofeedback, hypnosis and other techniques has suggested that some autonomic activities can be brought under voluntary control. The ANS consists of a sympathetic branch and a parasympathetic branch.
2. SOMATIC NERVOUS SYSTEM: The division of the peripheral nervous system that carries information between the CNS and the body's sensory systems and skeletal muscles. The somatic nervous system is associated with activities that are ordinarily considered voluntary.
BARBITURATES and Untoward Events
1. BARBITURATES: Sedative-hypnotics and act as CNS depressants. Barbiturates were once used to treat many medical and psychiatric disorders; however, due to their lethal effects and the development of safer and more effective drugs, they are now rarely
2. UNTOWARD EFFECTS: Slurred speech, nystagmus, dizziness, irritability and impaired motor and cognitive performance. An overdose can produce ataxia, confusion, agitation, disorientation, cold and clammy skin, dilated pupils, respiratory depression and death. Barbiturate usage causes a decrease in REM sleep, and abrupt cessation of usage can
cause an REM rebound and nightmares. Chronic use can produce tolerance,
psychological dependence and physical dependence. Without medical supervision, the
withdrawal symptoms can be life-threatening. Barbiturates are frequently involved in suicide and accidental death, particularly when they are used with alcohol or another sedative-hypnotic.
Broca and Wernickes Area
1. BROCA'S AREA: Motor speech area located in the frontal lobe just anterior to the motor cortex. Broca's area is involved with the articulation of speech. Damage results in
expressive aphasia, or an inability to produce speech.
2. WERNICKE'S AREA: Speech area located in the temporal lobe (usually left lobe).
Wernicke's area is responsible for the understanding of written and spoken language. Lesions produce receptive aphasia.
1. CATECHOLAMINE HYPOTHESIS: Hypothesis that depression is related to lower-than-normal levels of norepinephrine and dopamine and that mania is due to
excessive levels of these neurotransmitters.
2. DOPAMINE HYPOTHESIS: Hypothesis that Schizophrenia is due to oversensitivity of
dopamine receptors. The dopamine hypothesis is based on evidence that drugs that block dopamine receptors reduce schizophrenic symptoms and drugs that increase dopamine elicit or exacerbate schizophrenic symptoms.
Central and Peripheral Nervous System
1. CENTRAL NERVOUS SYSTEM (CNS): Consists of the nerve cells, fibers and tissues that make up the spinal cord and brain.
2. PERIPHERAL NERVOUS SYSTEM (PNS): Consists of the nervous system elements
ing outside of the spinal cord and brain. The peripheral nervous system includes the autonomic nervous system and the somatic nervous system.
Cerebral Hemispheres
The "cerebral hemispheres" (right and left) are the two halves of the cerebral cortex
(forebrain and midbrain). The cerebral hemispheres are involved in complex activities, such as abstract reasoning and language as well as sensory and motor functions.
1. CONTRALATERAL REPRESENTATION: The tendency of the two cerebral hemispheres to control the functions of the opposite (contralateral) side of the body.
2. LATERALIZATION OF FUNCTION: The tendency for each hemisphere to dominate over the other for specific functions. Lateralization of function also refers to the relationship between handedness and cerebral hemisphere dominance for certain functions. Nearly all
right-handers and more than half of all left-handers have left hemisphere dominance for language and right hemisphere dominance for spatial skills.
1. DIABETES INSIPIDUS: Disorder caused by insufficient antidiuretic hormone (ADH), resulting in an inability to retain body water (polyuria).
2. DIABETES MELLITUS: Disorder caused by insufficient insulin, resulting in an inability
of cells to use blood-sugar (glucose) and an accumulation of glucose in the blood. The symptoms of diabetes mellitus symptoms include fatigue, weakness and an increased susceptibility to infection.
Drug Interaction
The effects of a drug can be altered by the presence of other drugs; such drug
interactions can occur at the pharmacokinetic and/or pharmacodynamic level. In a
PHARMACOKINETIC INTERACTION, one drug interferes with the absorption, distribution,
transformation or excretion of another drug and thereby raises or lowers that drug's
concentration. When a PHARMACODYNAMIC INTERACTION occurs, one drug combines
with another drug and increases or decreases its effects at action sites.
1. CANNON-BARD THEORY (W.B. Cannon and P. Bard): Proposes that the bodily
reactions and experience of emotion occur simultaneously and are controlled primarily by the thalamus.
2. JAMES-LANGE THEORY: Proposes that emotions reflect experiences of visceral and muscular reactions to certain stimuli; e.g., "we feel afraid because we are running".
The side effects of anti-psychotic drugs that involve the extrapyramidal motor system; common effects include parkinsonism, akathisia, dystonia and tardive dyskinesia.
1. EXTRAPYRAMIDAL MOTOR SYSTEM: Motor system that controls and coordinates
motor activities required for locomotion, posture and balance. The extrapyramidal motor system includes the basal ganglia, substantia nigra, areas of the midbrain and motor neurons of the spinal cord.
2. PYRAMIDAL MOTOR SYSTEM: The motor nerve fibers that originate in the cortical
motor areas. The pyramidal motor system is involved in the regulation of voluntary and reflex activity of the muscles.
A pattern of congenital malformations that occurs in infants born to women suffering from severe, chronic alcoholism. Infants with FAS are typically shorter than normal, underweight, have defects of the skull and face, are hyperactive, display delayed motor and language development and are mentally retarded.
1. THALAMUS: Involved in the relay of sensory information to the neocortex and
extrapyramidal information from the cortex and in the mediation of attention, control of aggressive-defensive behavior.
2. HYPOTHALAMUS: Controls the ANS and endocrine system, mediates basic drives and regulates emotional expression.
3. BASAL GANGLIA: Involved in extrapyramidal control of motor activities.
4. LIMBIC SYSTEM: Involved in drive states and the experience of emotion. Its major structures are: (a) AMYGDALA: Involved in the control of emotional activities, particularly
the mediation of defensive-aggressive behaviors. (b) SEPTUM: Believed to be involved in the inhibition of emotional behavior. (c) HIPPOCAMPUS: Involved in response inhibition,
emotional behavior and memory (in humans).
5. CEREBRAL CORTEX: Outer covering of the cerebral hemispheres. Involved in sensory, motor and intellectual activities, and divided into two hemispheres (right and left). Each hemisphere is divided into four lobes: (a) FRONTAL: Contain motor area and association cortex. Believed to be involved in itiative, planning, empathy and tact. (b) PARIETAL: Contain the primary somatosensory cortex. (c) TEMPORAL: Contain the primary auditory
cortex. (d) OCCIPITAL: Contain the primary sensory cortex for vision.
General Adaptation Syndrome (Selye)
According to Selye, the human response to stress is mediated by adrenal-pituitary
secretions and involves three stages: alarm reaction, resistance and exhaustion. The
model predicts that prolonged stress may result in illness or death.
1. MEDULLA OBLONGATA: Involved in the mediation of vital autonomic activities,
including heart rate, blood pressure and respiration.
2. PONS: The rostral part of the hindbrain involved in the transmission of motor
information from higher brain areas and the spinal cord to the cerebellum and in the integration of movements involving both sides of the body.
3. CEREBELLUM: The large structure on the dorsal (back or posterior) aspect of the hindbrain. The cerebellum is involved in the extrapyramidal control of motor activities (e.g., coordination, balance, posture).
Hunger and Thirst
1. HUNGER AND OBESITY: Several factors have been linked to the control of hunger, including the hypothalamus, which exerts an inhibitory influence on feeding. Human obesity is only occasionally due to a malfunctioning hypothalamus, a glandular disturbance, or other physiological defect. Explanations for obesity include: (a) Obese
individuals have an unusually large number of lipocytes (fat cells) apparently as a result of
hereditary and/or environmental factors. (b) SET POINT THEORY suggests that the body has a mechanism that regulates body weight; the mechanism of obese people may be set,
as a result of hereditary and/or environmental factors, at a high level. (c) Some propose that stress and other emotional states play an important role; the tendency to eat in response to stress may be due to physiological mechanisms and/or to learning. (d)
Schachter (1968, 1971) has suggested that overweight people respond with hunger not only to appropriate physiological cues but also to a variety of external cues; e.g., time of
day, the sight of food.
2. THIRST: Bilateral lesions of the lateral hypothalamic area (LHA) produce adipsia, a
cessation of drinking. Electrical stimulation causes water-satiated animals to drink.
Huntington's chorea
"Huntington's chorea" is a genetic degenerative brain disease associated with low levels of GABA in the substantia nigra and basal ganglia. It involves disturbances of movement and gradual mental deterioration.
1. HYPERTHYROIDISM: Caused by hypersecretion of thyroxin by the thyroid gland and characterized by speeded-up metabolism, elevated body temperature, accelerated heart rate, increased appetite with weight loss, exophthalmos, nervousness and insomnia.
Hyperthyroidism occurs most commonly between the ages of 20 and 40 and is more
common in women than men.
2. HYPOTHYROIDISM: Caused by hyposecretion of thyroxin by the thyroid gland and
characterized by slowed metabolism, slowed heart rate, lethargy, lowered body
temperature and depression.
"Hyperventilation" is an increased frequency of breathing that leads to an excessive intake of oxygen and expulsion of carbon dioxide. The resulting hypocapnia and respiratory alkalosis produce dizziness, faintness, tingling and numbness in the extremities
and psychomotor impairment.
Kluver-Bucy syndrome
The "Kluver-Bucy syndrome" is produced by bilateral removal of the temporal lobes, including the amygdala and hippocampus. It is characterized by compulsive oral investigatory behavior, docility, visual agnosia, loss of social dominance and profound hypersexuality.
Learning and Memory
Because no specific brain area has been consistently linked with the formation (learning) or retention (memory) of memory traces (engrams), some researchers have proposed that these functions occur diffusely throughout the brain. For example: (a) THE PRINCIPLE OF MASS ACTION: Proposes that the degree of memory or performance deficit following
cortical damage is dependent on the amount of tissue damaged. (b) THE PRINCIPLE OF
EQUIPOTENTIALITY: Proposes that, for many tasks, the various cortical areas contribute to learning and memory approximately equally. Though specific areas of the brain have not been identified as the location of engrams, several subcortical areas have been
implicated in the processes of learning and memory. In humans, damage to the certain of the HIPPOCAMPUS is associated with memory loss.
Lithium and Untoward Events
1. LITHIUM: Used in the treatment and prophylaxis of depressive, hypomanic and manic phases of Bipolar Mood Disorders.
2. UNTOWARD EFFECTS: Muscle weakness, fine hand tremor, fatigue, nausea, vomiting,
diarrhea, weight gain and polydipsia. The major danger is that the dose will be too high, resulting in lithium poisoning; for this reason, serum levels of lithium must be checked regularly. Signs of lithium toxicity include coarse tremor, marked lethargy, slurred speech, ataxia, confusion, convulsions and coma. Because the potential for toxicity is increased
by sodium depletion, the individual's diet must be monitored carefully and diuretics should be avoided. Because lithium has adverse effects on certain body tissues, it is
contraindicated for individuals with cardiovascular, renal, liver and gastrointestinal
problems. Lithium is not associated with tolerance or dependence.
1. NEUROLEPTICS, OR ANTI-PSYCHOTICS: A.k.a. major tranquilizers. Phenothiazines (e.g., Chlorpromazine) are commonly used to alleviate the symptoms of Schizophrenia.
2. UNTOWARD EFFECTS: (a) ANTICHOLINERGIC: Dry mouth, blurred vision, tachycardia, urinary retention and constipation. (b) Orthostatic Hypotension: Abnormally Iow blood pressure when the person stands up. (c) Sedation. (d) EXTRAPYRAMIDAL:
Parkinsonism, akathisia and acute dystonia. Parkinsonism resembles Parkinson's disease (i.e., akinesia, tremor, muscle rigidity, shuffling gait). These effects can often be alleviated with antiparkinsonian agents. TARDIVE DYSKINESIA (rhythmical, stereotyped
movements, lip-smacking) is the most serious extrapyramidal effect; it is usually late occurring and its symptoms are often irreversible unless recognized early and treatment is stopped. Antiparkinsonian drugs may exacerbate its symptoms. (e) Other potential side effects include jaundice, blood dyscrasias, rashes, menorrhea, infertility, impotence, increased appetite, weight gain, insomnia and depression. (f) Neuroleptics do not result in
tolerance or dependence, but abrupt withdrawal may cause sleep disturbances and cholinergic rebound (abdominal cramps, diarrhea and increased salivation).
Nerve Cell
The type of cell most directly involved in mental processes. A neuron is specialized for the
conduction of electrochemical signals that carry information from one part of the body to
another. It consists of three main parts: soma (cell body); dendrites (receive information from other cells and conduct it toward the soma); and axon (involved in the transmission of information away from the soma toward other cells).
"Neurotransmitters" are chemical substances released from axon terminals; they diffuse across synapses and excite or inhibit receptor sites on adjacent cells.
1. ACh: Mediates neuromuscular transmission and parasympathetic arousal and is found in the CNS and PNS.
2. GABA: The most common inhibitory neurotransmitter in the CNS. Low levels of GABA in the motor region are associated with Huntington's chorea.
3. NOREPINEPHRINE: Mediates the activity of the sympathetic nervous system and plays a role in the regulation of eating, sleep and positive reinforcement. Norepinephrine is also
a hormone released by the adrenal medulla.
4. DOPAMINE: Involved in inhibitory motor regulation and motivational/emotional
functions. Insufficient dopamine in the basal ganglia is believed to underlie Parkinson's
disease. Excessive dopamine may be involved in the development of Schizophrenia.
5. SEROTONIN: Implicated in the suppression of the arousing effects of the ARAS, the regulation of temperature, hunger, aggression and sexual behavior and in the Mood Disorders and Schizophrenia.
6. EPINEPHRINE: Found in the neurons involved in sympathetic nervous system
activities. Epinephrine is also a hormone secreted by the adrenal medulla, particularly during periods of stress.
Parasympathetic and Sympathetic Nervous System
1. PARASYMPATHETIC NERVOUS SYSTEM: The division of the autonomic nervous system involved in the conservation of energy and relaxation. Activation of the
parasympathetic nervous system is associated with slowing of heart rate, lowered blood pressure, contraction of pupils, reduction of sweat gland output and increased activity of the digestive system.
2. SYMPATHETIC NERVOUS SYSTEM (SNS): The division of the autonomic nervous
system involved in the mediation of the flight or fight (emergency) reaction. Activation of the SNS produces increased heart rate, pupil dilation, increased blood sugar and
inhibition of digestive processes.
Parkinson's Disease
A disease of the basal ganglia characterized by muscle weakness, tremor and difficulty initiating and maintaining voluntary movements. Parkinson's disease is believed to be due to inadequate levels of dopamine.
"Psychophysics" is the study of the relationship between physical stimulus magnitudes
and their corresponding psychological sensations. It is concerned with determining
absolute thresholds (the minimum stimulus required to produce a specific sensation) and how people perceive changes in stimulus intensities.
1. FECHNER'S LAW: Psychophysical law that states that physical stimulus changes are
logarithmically related to their psychological sensations.
2. WEBER'S LAW: Psychophysical law that states that the just noticeable difference in
stimulus intensity is a constant proportion of the initial stimulus intensity.
3. STEVEN'S POWER LAW: Psychophysical law that proposes that the magnitude of a sensation is equal to the physical magnitude of the stimulus producing the sensation raised to a certain power (exponent), which varies, depending on the specific sensation being measured.
Involve physical symptoms that are caused or maintained by emotional factors.
1. PEPTIC ULCERS: More common in men, usually occur in young and middle-aged adults and heavy cigarette smokers and has been associated with stress.
2. HYPERTENSION: Secondary hypertension is diagnosed when high blood pressure is
due to a known disease. Essential hypertension is diagnosed when high blood pressure is not due to a known physiological cause; it tends to run in families and is more common in
men than women and in blacks than whites. Factors linked to a high risk for essential
hypertension include stress, over-use of table salt, obesity and cigarette smoking.
3. MIGRAINE HEADACHES: Usually begin before age 40 and attacks often stop after
middle age. Tend to run in families and are slightly more common in women. Often
triggered by anxiety, fatigue, allergens, or bright lights.
4. PREMENSTRUAL SYNDROME (PMS): Physiological theories of PMS usually emphasize the role of progesterone. Some studies suggest that PMS involves mild symptoms or symptoms in only a small percentage of women, while others report severe symptoms.
5. BRONCHIAL ASTHMA: Often caused by physical (e.g., allergens) and psychological
(e.g., strong emotional reactions) factors. Asthma can be classically or operantly conditioned. Approximately 60% of asthmatics are under age 17 and boys are twice as
Iikely to suffer from asthma. At least 40% of asthmatics show partial or total remission of
symptoms as they grow older.
6. HYPERVENTILATION: Often triggered by anxiety or other emotional states and can usually be relieved through relaxation, rebreathing into a paper bag, or sedation.
1. REM SLEEP: Rapid eye movement sleep. The sleep stage characterized by an
activated EEG, dreaming, flaccid muscles and deep sleep. REM sleep is also known as paradoxical sleep and D-sleep. REM-sleep makes up approximately 25% of the total night's sleep.
2. NON-REM SLEEP: Non-rapid eye movement sleep. Encompasses sleep Stages 1
through 4, which are characterized by a slow-wave EEG pattern. Non-REM Sleep makes up approximately 75% of the total sleep time.
Reticular Formation
The "reticular formation" is a complex structure found throughout the core of the
brainstem. It is involved with extrapyramidal motor functions, affective states and arousal.
reticular formation, which are involved in wakefulness, arousal and attention.
2. DRAS (DESCENDING RETICULAR ACTIVATING SYSTEM): The descending fibers of the reticular formation, which diminish arousal responses.
1. RITALIN METHYLPHENIDATE: A mild CNS stimulant used primarily for the treatment
of hyperactivity.
2. UNTOWARD EFFECTS: Most commonly, anorexia and insomnia. Less commonly,
abdominal pain, headache, tachycardia and tearfulness. The long-term use of Ritalin for hyperactivity is controversial due to its apparent growth suppressing effects. Some research, however, has suggested that the suppression is temporary and that methylphenidate is less likely to suppress growth than the amphetamines. Some authorities recommend regular "drug holidays" to provide periods for growth "rebound" and to
determine whether continued drug treatment is required. When Ritalin is administered to children, tolerance to its appetite-suppressing effects often develops in the first few weeks. However, tolerance to its calming effects rarely occurs. There is little evidence that use by hyperactive children produces dependence or abuse.
Chemical compounds used as sedatives and/or hypnotics. The behavioral effects of
sedative-hypnotics are dose dependent and range from general tranquilizing effects to
sedation, sleep, coma and death. Examples include barbiturates, minor tranquilizers and
Septal Rage Syndrome
Refers to the behavior change resulting from bilateral lesioning of the septal area (septum). The septal rage syndrome is characterized by hyperemotionality and
indiscriminate attack behavior.
Sexual Arousal and the Effects of Aging
Though the majority of elderly people continue to enjoy and engage in sexual activity, changes in sexuality do occur in later life. Sexuality is often experienced as more diffuse
and sensual, and older people often state that affection and physical closeness have become increasingly more important. In women, as a result of estrogen depletion following menopause, the uterus and cervix shrink in size, vaginal lubrication decreases and the vaginal walls become thinner. Men experience a steady decline in testosterone as they
grow older. Elderly men take longer to achieve an erection and ejaculate with less force but can maintain an erection for a longer period of time.
Refers to the cutaneous, muscular and visceral sensations of pressure, pain, touch, cold and warmth. Unlike other sensations, PAIN is not linked with any single type of stimulus, but, instead, is elicited by several types of stimuli including pressure, heat and cold. Further, pain is not only a function of local skin sensation but is also mediated by emotions. According to the GATE CONTROL THEORY of pain, a "gate" mechanism in the
spinal cord mediates the perception of pain. This theory has been used to explain the effectiveness of acupuncture. Studies investigating pain relief mechanisms have identified
similarities between the analgesia produced by morphine and the analgesia produced by the electrical stimulation of certain areas of the brain. Such studies suggest that there are
naturally-occurring pain-killing substances in the brain; e.g., endorphins and enkephalins tend to inhibit the perception of pain.
Synergistic Effects
A type of drug interaction. For example, synergistic (superadditive) effects are produced by a combination of alcohol and another sedative-hypnotic.
Tolerance and Withdrawal
1. TOLERANCE: The state of progressively decreasing responsiveness to a drug, so that larger and larger doses are required to produce the same effects. Tolerance does not
necessarily develop equally to all pharmacological effects of a drug.
2. WITHDRAWAL: Psychological and/or physical syndrome caused by the abrupt
cessation of the use of a drug in an habituated drug user. Specific symptoms of
withdrawal vary, depending on the drug type.
1. TRICHROMATIC THEORY: Theory of color vision that proposes that color vision is
mediated by three types of cones: red, green and blue. A combination of output from
these cells determines the colors perceived.
2. OPPONENT PROCESS THEORY: Theory of color vision that proposes that color vision
is mediated by three kinds of receptors: red/green, blue/yellow and black/white. Firing rates in these cells change in response to different wavelengths in an opponent manner (e.g., activation of red receptors inhibits green receptors).

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