🧠 Psychology MCQs (1–100)
Preparing for psychology exams like AP Psychology, GRE Subject Test, A-levels, or competitive exams worldwide? This set of 100 MCQs with answers and concise explanations cover important topics such as classical and operant conditioning, major schools of psychology, famous experiments, brain functions, memory systems, and key psychologists like Freud, Pavlov, Skinner, Maslow, and William James.
1. Who is considered the “father of psychology” as an independent science?
(A) Sigmund Freud
(B) Wilhelm Wundt ✅
(C) William James
(D) John B. Watson
Explanation: Wilhelm Wundt established the first psychology laboratory in Leipzig, Germany in 1879, marking psychology’s formal beginning as a science.
2. Psychology is best defined as the scientific study of:
(A) Mental illness
(B) The soul
(C) Behavior and mental processes ✅
(D) Human biology
Explanation: Modern psychology studies both observable behavior and internal mental processes such as thoughts, emotions, and perceptions.
3. Who introduced the concept of “stream of consciousness”?
(A) Sigmund Freud
(B) William James ✅
(C) B.F. Skinner
(D) Ivan Pavlov
Explanation: William James emphasized that consciousness is a continuous, flowing process rather than separate parts.
4. The method used by Wundt to study mental processes was:
(A) Behaviorism
(B) Psychoanalysis
(C) Introspection ✅
(D) Classical conditioning
Explanation: Wundt used introspection, where participants reported their thoughts and sensations to analyze consciousness.
5. Which school of psychology focused on observable behavior rather than mental processes?
(A) Structuralism
(B) Functionalism
(C) Behaviorism ✅
(D) Humanism
Explanation: Behaviorism, led by John B. Watson and later B.F. Skinner, studied only observable behavior, rejecting introspection.
6. The “id, ego, and superego” are concepts from which psychological approach?
(A) Humanistic
(B) Psychoanalytic ✅
(C) Cognitive
(D) Behavioral
Explanation: Freud’s psychoanalytic theory explained personality using the unconscious (id), reality principle (ego), and morality (superego).
7. Who developed the theory of classical conditioning?
(A) Ivan Pavlov ✅
(B) B.F. Skinner
(C) Albert Bandura
(D) Carl Rogers
Explanation: Ivan Pavlov, a Russian physiologist, discovered classical conditioning through experiments with dogs and salivation.
8. Which psychologist is associated with operant conditioning?
(A) John Watson
(B) Sigmund Freud
(C) B.F. Skinner ✅
(D) Jean Piaget
Explanation: B.F. Skinner introduced operant conditioning, where behavior is shaped by reinforcement and punishment.
9. The humanistic approach in psychology emphasizes:
(A) Free will and personal growth ✅
(B) Biological instincts
(C) Unconscious desires
(D) Observable behavior only
Explanation: Humanistic psychologists like Carl Rogers and Abraham Maslow stressed individual potential, free will, and self-actualization.
10. Which method is most commonly used to collect data in psychology?
(A) Dreams
(B) Case studies
(C) Experiments ✅
(D) Hypnosis
Explanation: Experiments allow psychologists to test hypotheses under controlled conditions and establish cause-and-effect relationships.
11. Who is regarded as the father of American psychology?
(A) William James ✅
(B) John Watson
(C) Edward Titchener
(D) Carl Rogers
Explanation: William James was a pioneer of functionalism and wrote Principles of Psychology (1890), shaping psychology in America.
12. Structuralism in psychology was developed by:
(A) Wilhelm Wundt
(B) Edward Titchener ✅
(C) John Dewey
(D) Max Wertheimer
Explanation: Edward Titchener, a student of Wundt, developed structuralism focusing on analyzing the basic components of consciousness.
13. Functionalism emphasized:
(A) Purpose of behavior and mental processes ✅
(B) Unconscious desires
(C) Brain structures only
(D) Statistical methods
Explanation: Functionalists, led by William James and John Dewey, studied how mental processes help individuals adapt to their environment.
14. The “Gestalt” school of psychology focused on:
(A) Individual parts of consciousness
(B) The whole experience ✅
(C) Dreams and unconsciousness
(D) Behavioral learning only
Explanation: Gestalt psychologists argued that perception and experience should be studied as organized wholes, not parts.
15. Which psychological approach emphasizes learning through observation?
(A) Behaviorism
(B) Cognitive
(C) Social Learning ✅
(D) Humanism
Explanation: Albert Bandura’s Social Learning Theory stressed that behavior can be learned by observing and imitating others.
16. The term “tabula rasa” (blank slate) is linked with:
(A) John Locke ✅
(B) Sigmund Freud
(C) Carl Jung
(D) Charles Darwin
Explanation: John Locke argued that humans are born with a blank mind, shaped by experiences, influencing later psychological thought.
17. Cognitive psychology focuses on:
(A) Emotions only
(B) Mental processes like thinking, memory, problem-solving ✅
(C) Reflexes
(D) Personality traits
Explanation: Cognitive psychology studies internal processes such as attention, memory, reasoning, and problem-solving.
18. The hierarchy of needs was proposed by:
(A) Carl Rogers
(B) Sigmund Freud
(C) Abraham Maslow ✅
(D) Erik Erikson
Explanation: Maslow’s hierarchy explains human motivation, starting from physiological needs to self-actualization.
19. Psychology became officially recognized as a science in which year?
(A) 1850
(B) 1879 ✅
(C) 1900
(D) 1920
Explanation: In 1879, Wilhelm Wundt established the first psychology laboratory in Leipzig, Germany.
20. Which of the following is NOT a goal of psychology?
(A) Description
(B) Prediction
(C) Manipulation ✅
(D) Control
Explanation: The main goals of psychology are description, explanation, prediction, and control of behavior—not manipulation.
21. Who is considered the founder of psychoanalysis?
(A) Sigmund Freud ✅
(B) Carl Jung
(C) Alfred Adler
(D) Erik Erikson
Explanation: Freud developed psychoanalysis, focusing on unconscious motives, childhood experiences, and dream analysis.
22. Which psychologist introduced the concept of “collective unconscious”?
(A) Sigmund Freud
(B) Carl Jung ✅
(C) Karen Horney
(D) Albert Ellis
Explanation: Carl Jung believed humans share a collective unconscious filled with archetypes.
23. The humanistic approach in psychology emphasizes:
(A) Unconscious desires
(B) Free will and personal growth ✅
(C) Conditioning
(D) Brain chemistry
Explanation: Humanistic psychologists like Maslow and Rogers focus on self-actualization, free will, and human potential.
24. Who is regarded as the father of behaviorism?
(A) John B. Watson ✅
(B) B. F. Skinner
(C) Ivan Pavlov
(D) Edward Thorndike
Explanation: Watson promoted behaviorism, arguing that psychology should study observable behavior only.
25. Which psychologist conducted the famous “Little Albert” experiment?
(A) John Watson ✅
(B) B. F. Skinner
(C) Ivan Pavlov
(D) Albert Bandura
Explanation: John Watson and Rosalie Rayner conditioned Little Albert to fear white rats, showing classical conditioning in humans.
26. Ivan Pavlov is best known for his work on:
(A) Operant conditioning
(B) Classical conditioning ✅
(C) Cognitive psychology
(D) Humanistic psychology
Explanation: Pavlov demonstrated how dogs could be conditioned to salivate to a bell, laying foundations for classical conditioning.
27. B. F. Skinner is associated with:
(A) Observational learning
(B) Operant conditioning ✅
(C) Psychoanalysis
(D) Gestalt theory
Explanation: Skinner studied reinforcement and punishment in shaping behavior through operant conditioning.
28. Which of the following is an example of a reinforcement schedule?
(A) Fixed ratio ✅
(B) Dream analysis
(C) Collective unconscious
(D) Hierarchy of needs
Explanation: Fixed ratio, variable ratio, fixed interval, and variable interval are reinforcement schedules in operant conditioning.
29. The term “cognitive dissonance” was introduced by:
(A) Leon Festinger ✅
(B) Albert Bandura
(C) Stanley Milgram
(D) Carl Rogers
Explanation: Festinger explained how individuals feel discomfort when holding contradictory beliefs or attitudes.
30. Who is known for the obedience experiment using shocks?
(A) Stanley Milgram ✅
(B) Philip Zimbardo
(C) Solomon Asch
(D) Albert Ellis
Explanation: Milgram’s study showed people’s tendency to obey authority even when actions harm others.
31. The Stanford Prison Experiment was conducted by:
(A) Philip Zimbardo ✅
(B) Stanley Milgram
(C) Solomon Asch
(D) Kurt Lewin
Explanation: Zimbardo’s experiment highlighted how social roles and environments influence behavior.
32. The “Bobo Doll” experiment demonstrated:
(A) Operant conditioning
(B) Observational learning ✅
(C) Free association
(D) Gestalt principles
Explanation: Albert Bandura showed children imitate aggressive behavior after observing adults.
33. The term “introversion” and “extraversion” were introduced by:
(A) Carl Jung ✅
(B) Sigmund Freud
(C) Alfred Adler
(D) William James
Explanation: Jung introduced personality dimensions of introversion and extraversion.
34. Erik Erikson is best known for his theory of:
(A) Psychosexual stages
(B) Psychosocial development ✅
(C) Conditioning
(D) Archetypes
Explanation: Erikson proposed 8 stages of psychosocial development, focusing on identity and social relationships.
35. The term “self-actualization” is linked to:
(A) Abraham Maslow ✅
(B) B. F. Skinner
(C) Sigmund Freud
(D) John Watson
Explanation: Maslow described self-actualization as the fulfillment of one’s potential.
36. Which type of psychologist studies workplace behavior?
(A) Clinical psychologist
(B) Industrial-organizational psychologist ✅
(C) Forensic psychologist
(D) Educational psychologist
Explanation: I/O psychologists apply psychology to workplace behavior, motivation, and productivity.
37. Psychology uses the scientific method because:
(A) It ensures objectivity and reliability ✅
(B) It avoids testing
(C) It focuses only on opinions
(D) It studies dreams only
Explanation: The scientific method helps psychology remain empirical and evidence-based.
38. The term “operant conditioning chamber” is also called:
(A) Skinner box ✅
(B) Pavlov box
(C) Gestalt chamber
(D) Freud box
Explanation: B. F. Skinner used the operant chamber to study reinforcement and punishment.
39. Who developed the hierarchy of moral reasoning?
(A) Lawrence Kohlberg ✅
(B) Jean Piaget
(C) Erik Erikson
(D) Lev Vygotsky
Explanation: Kohlberg proposed stages of moral development from pre-conventional to post-conventional levels.
40. The “placebo effect” occurs when:
(A) A treatment works because of expectation ✅
(B) A drug works biologically only
(C) A person resists therapy
(D) A patient rejects treatment
Explanation: The placebo effect happens when improvement occurs due to belief in treatment, not the treatment itself.
41. Who is considered the first American psychologist?
(A) Sigmund Freud
(B) William James ✅
(C) John Watson
(D) Edward Titchener
Explanation: William James is regarded as the father of American psychology. He wrote Principles of Psychology and emphasized functionalism.
42. Which school of psychology focused on breaking down mental processes into basic elements?
(A) Functionalism
(B) Structuralism ✅
(C) Behaviorism
(D) Humanism
Explanation: Structuralism, developed by Wundt and Titchener, analyzed consciousness into sensations and feelings.
43. The “whole is greater than the sum of its parts” is the principle of:
(A) Behaviorism
(B) Gestalt psychology ✅
(C) Psychoanalysis
(D) Humanism
Explanation: Gestalt psychology, introduced in Germany, studied perception and argued that people perceive patterns as unified wholes.
44. Who developed the concept of defense mechanisms?
(A) Carl Jung
(B) Sigmund Freud ✅
(C) Alfred Adler
(D) Erik Erikson
Explanation: Freud explained defense mechanisms (like repression, denial, projection) as unconscious ways to reduce anxiety.
45. Which defense mechanism involves attributing one’s own thoughts to others?
(A) Repression
(B) Projection ✅
(C) Displacement
(D) Regression
Explanation: Projection occurs when people assign their own unacceptable feelings to others.
46. In Pavlov’s classical conditioning, the bell represents:
(A) Unconditioned stimulus
(B) Conditioned stimulus ✅
(C) Response
(D) Reinforcer
Explanation: The bell, after pairing with food, became a conditioned stimulus that triggered salivation.
47. In operant conditioning, a negative reinforcement:
(A) Adds a reward
(B) Removes an unpleasant stimulus ✅
(C) Punishes behavior
(D) Stops learning
Explanation: Negative reinforcement strengthens behavior by removing something unpleasant (e.g., seatbelt alarm stops when belt is fastened).
48. The famous “Hierarchy of Needs” pyramid was created by:
(A) Erik Erikson
(B) Abraham Maslow ✅
(C) Carl Rogers
(D) John Watson
Explanation: Maslow described human motivation from basic physiological needs to self-actualization.
49. Which psychologist is known for client-centered therapy?
(A) Abraham Maslow
(B) Carl Rogers ✅
(C) Albert Ellis
(D) Aaron Beck
Explanation: Carl Rogers emphasized empathy, unconditional positive regard, and self-concept in therapy.
50. Who introduced the concept of “cognitive maps” in rats?
(A) John Watson
(B) Edward Tolman ✅
(C) Ivan Pavlov
(D) B. F. Skinner
Explanation: Tolman showed rats formed cognitive maps of mazes, highlighting latent learning.
51. The “strange situation” test to study attachment styles was developed by:
(A) Jean Piaget
(B) Mary Ainsworth ✅
(C) John Bowlby
(D) Erik Erikson
Explanation: Ainsworth studied secure, avoidant, and ambivalent attachment in children.
52. The term “tabula rasa” (blank slate) is associated with:
(A) John Locke ✅
(B) Sigmund Freud
(C) Carl Jung
(D) B. F. Skinner
Explanation: Locke described the human mind as a blank slate shaped by experience.
53. Cognitive psychology mainly focuses on:
(A) Unconscious drives
(B) Thought processes ✅
(C) Behavior only
(D) Self-actualization
Explanation: Cognitive psychology studies memory, perception, problem-solving, and decision-making.
54. Which psychologist proposed the “law of effect”?
(A) Ivan Pavlov
(B) Edward Thorndike ✅
(C) John Watson
(D) Albert Bandura
Explanation: Thorndike’s law of effect states behaviors followed by rewards are strengthened, while punished behaviors weaken.
55. Which research method provides detailed study of one person?
(A) Case study ✅
(B) Experiment
(C) Survey
(D) Observation
Explanation: Case studies give deep insights into individuals, but may lack generalization.
56. Random assignment in experiments is used to:
(A) Increase bias
(B) Reduce differences between groups ✅
(C) Prove causation directly
(D) Avoid replication
Explanation: Random assignment ensures experimental and control groups are similar, increasing reliability.
57. A double-blind study helps to avoid:
(A) Placebo effect ✅
(B) Natural observation
(C) Case study errors
(D) Experimental design
Explanation: Double-blind studies prevent both participants and researchers from knowing group assignments, reducing bias.
58. The first psychological laboratory was established in:
(A) France
(B) Germany ✅
(C) USA
(D) UK
Explanation: Wilhelm Wundt set up the first lab in Leipzig, Germany, in 1879.
59. Which term describes the tendency to believe we knew an outcome all along?
(A) Confirmation bias
(B) Hindsight bias ✅
(C) Anchoring bias
(D) Availability bias
Explanation: Hindsight bias is the “I knew it all along” effect after outcomes are revealed.
60. Which type of psychologist deals with diagnosing and treating mental illness?
(A) Clinical psychologist ✅
(B) I/O psychologist
(C) Social psychologist
(D) Counseling psychologist
Explanation: Clinical psychologists specialize in assessing and treating psychological disorders.
61. Which psychologist conducted the “Little Albert” experiment on conditioned fear?
(A) Ivan Pavlov
(B) John Watson ✅
(C) B. F. Skinner
(D) Edward Thorndike
Explanation: John Watson and Rosalie Rayner conditioned a child (“Little Albert”) to fear a white rat, showing classical conditioning in humans.
62. Who introduced the concept of “collective unconscious”?
(A) Sigmund Freud
(B) Carl Jung ✅
(C) Alfred Adler
(D) Karen Horney
Explanation: Carl Jung believed in a collective unconscious containing archetypes shared by all humans.
63. The “ego” operates on which principle?
(A) Reality principle ✅
(B) Pleasure principle
(C) Morality principle
(D) Instinct principle
Explanation: According to Freud, the ego balances demands of id and superego using the reality principle.
64. Who is the founder of psychoanalysis?
(A) Sigmund Freud ✅
(B) Carl Jung
(C) Erik Erikson
(D) Karen Horney
Explanation: Freud pioneered psychoanalysis, focusing on unconscious motives, childhood, and dreams.
65. Which of the following is a projective test?
(A) MMPI
(B) Rorschach Inkblot Test ✅
(C) IQ Test
(D) Aptitude Test
Explanation: Rorschach Inkblot Test assesses personality through interpretation of ambiguous images.
66. Who emphasized “inferiority complex” in personality development?
(A) Alfred Adler ✅
(B) Carl Jung
(C) Erik Erikson
(D) Sigmund Freud
Explanation: Adler argued people strive to overcome feelings of inferiority through compensation.
67. Which approach focuses on free will and personal growth?
(A) Behaviorism
(B) Humanistic psychology ✅
(C) Cognitive psychology
(D) Psychoanalysis
Explanation: Humanistic psychologists like Maslow and Rogers stressed individual potential and self-actualization.
68. Which part of the brain regulates basic drives like hunger and thirst?
(A) Cerebellum
(B) Hypothalamus ✅
(C) Hippocampus
(D) Amygdala
Explanation: The hypothalamus controls biological drives, body temperature, and hormones.
69. The hippocampus plays a crucial role in:
(A) Emotional regulation
(B) Memory formation ✅
(C) Breathing
(D) Reflexes
Explanation: The hippocampus is central to forming long-term declarative memories.
70. The amygdala is linked with:
(A) Fear and aggression ✅
(B) Balance
(C) Memory storage
(D) Vision
Explanation: The amygdala regulates fear, emotional learning, and threat responses.
71. The nervous system is divided into:
(A) Central and peripheral ✅
(B) Sympathetic and parasympathetic
(C) Brain and spinal cord only
(D) Autonomic and somatic only
Explanation: The nervous system consists of the central (brain + spinal cord) and peripheral systems.
72. Which neurotransmitter is associated with pleasure and reward?
(A) Serotonin
(B) Dopamine ✅
(C) Acetylcholine
(D) GABA
Explanation: Dopamine regulates motivation, pleasure, and reward-seeking behavior.
73. Low levels of serotonin are linked to:
(A) Schizophrenia
(B) Depression ✅
(C) Parkinson’s disease
(D) Memory loss
Explanation: Serotonin imbalance is associated with mood disorders, especially depression.
74. The split-brain research was pioneered by:
(A) Carl Rogers
(B) Roger Sperry ✅
(C) Jean Piaget
(D) Noam Chomsky
Explanation: Roger Sperry studied patients with severed corpus callosum, revealing hemisphere specialization.
75. Which lobe of the brain is responsible for decision-making and planning?
(A) Frontal lobe ✅
(B) Parietal lobe
(C) Occipital lobe
(D) Temporal lobe
Explanation: The frontal lobe handles executive functions, reasoning, and voluntary movements.
76. The occipital lobe mainly processes:
(A) Hearing
(B) Vision ✅
(C) Emotions
(D) Balance
Explanation: The occipital lobe, at the back of the brain, is responsible for visual processing.
77. The temporal lobe is primarily associated with:
(A) Hearing ✅
(B) Smell
(C) Touch
(D) Vision
Explanation: Temporal lobes regulate hearing, language, and memory functions.
78. Broca’s area in the brain is responsible for:
(A) Language comprehension
(B) Speech production ✅
(C) Visual processing
(D) Memory recall
Explanation: Broca’s area, in the frontal lobe, helps in speech production; damage causes expressive aphasia.
79. Wernicke’s area is involved in:
(A) Emotional control
(B) Language comprehension ✅
(C) Motor skills
(D) Reflexes
Explanation: Wernicke’s area, in the temporal lobe, is vital for understanding spoken and written language.
80. Which research method studies behavior in its natural environment without manipulation?
(A) Survey
(B) Experiment
(C) Naturalistic observation ✅
(D) Case study
Explanation: Naturalistic observation records real-world behavior without interference, increasing ecological validity.
81. Which psychological perspective emphasizes observable behavior?
(A) Cognitive psychology
(B) Behaviorism ✅
(C) Psychoanalysis
(D) Humanistic psychology
Explanation: Behaviorism, championed by Watson and Skinner, focused only on measurable behaviors, not mental processes.
82. Who proposed the Hierarchy of Needs theory?
(A) Carl Rogers
(B) Abraham Maslow ✅
(C) Erik Erikson
(D) Sigmund Freud
Explanation: Maslow created the hierarchy of needs, with self-actualization at the top.
83. Which psychologist is associated with client-centered therapy?
(A) Carl Rogers ✅
(B) Albert Bandura
(C) B. F. Skinner
(D) Abraham Maslow
Explanation: Rogers developed person-centered therapy, focusing on unconditional positive regard and empathy.
84. Which research method provides an in-depth study of one person?
(A) Survey
(B) Case study ✅
(C) Experiment
(D) Naturalistic observation
Explanation: Case studies provide detailed insights into rare conditions but lack generalizability.
85. A test that measures what it is intended to measure has:
(A) Validity ✅
(B) Reliability
(C) Objectivity
(D) Standardization
Explanation: Validity ensures that the test actually measures the intended construct.
86. A test that produces consistent results over time has:
(A) Validity
(B) Reliability ✅
(C) Objectivity
(D) Accuracy
Explanation: Reliability refers to consistency and stability of results.
87. Who conducted the obedience experiments with shocks?
(A) Philip Zimbardo
(B) Stanley Milgram ✅
(C) Solomon Asch
(D) Kurt Lewin
Explanation: Milgram’s experiments showed people’s strong obedience to authority, even against morals.
88. Which psychologist conducted the Stanford Prison Experiment?
(A) Stanley Milgram
(B) Philip Zimbardo ✅
(C) Albert Bandura
(D) Solomon Asch
Explanation: Zimbardo studied power and authority in a simulated prison, which had extreme outcomes.
89. Solomon Asch is known for which famous study?
(A) Obedience
(B) Conformity ✅
(C) Memory
(D) Conditioning
Explanation: Asch’s conformity experiment showed people conform to group pressure even when wrong.
90. The “Bobo doll” experiment demonstrated:
(A) Classical conditioning
(B) Operant conditioning
(C) Observational learning ✅
(D) Psychoanalysis
Explanation: Albert Bandura showed children imitate aggressive behavior when they observe adults doing it.
91. What is the main focus of cognitive psychology?
(A) Behavior
(B) Unconscious conflicts
(C) Mental processes ✅
(D) Emotions only
Explanation: Cognitive psychology studies how people think, learn, and remember.
92. Which memory system holds information for a few seconds?
(A) Long-term memory
(B) Sensory memory ✅
(C) Short-term memory
(D) Episodic memory
Explanation: Sensory memory briefly stores incoming sensory data before processing.
93. Short-term memory typically holds how many items?
(A) 3 ± 1
(B) 7 ± 2 ✅
(C) 10 ± 2
(D) Unlimited
Explanation: George Miller suggested short-term memory holds 7 ± 2 chunks of information.
94. The process of transforming sensory input into a neural signal is called:
(A) Encoding ✅
(B) Retrieval
(C) Storage
(D) Association
Explanation: Encoding converts sensory information into memory.
95. Which psychologist studied classical conditioning in dogs?
(A) B. F. Skinner
(B) Ivan Pavlov ✅
(C) John Watson
(D) Edward Thorndike
Explanation: Pavlov demonstrated classical conditioning through salivation experiments with dogs.
96. Who introduced the Law of Effect?
(A) Ivan Pavlov
(B) John Watson
(C) Edward Thorndike ✅
(D) B. F. Skinner
Explanation: Thorndike’s Law of Effect states behaviors followed by positive outcomes are repeated.
97. Operant conditioning is most closely linked with:
(A) Ivan Pavlov
(B) B. F. Skinner ✅
(C) Carl Jung
(D) Abraham Maslow
Explanation: Skinner studied reinforcement and punishment in shaping behavior.
98. The variable that is manipulated in an experiment is called:
(A) Dependent variable
(B) Independent variable ✅
(C) Control variable
(D) Extraneous variable
Explanation: Independent variable is manipulated to see its effect on the dependent variable.
99. The variable that is measured in an experiment is called:
(A) Dependent variable ✅
(B) Independent variable
(C) Control variable
(D) Extraneous variable
Explanation: Dependent variable is the outcome affected by the independent variable.
100. In psychology, a placebo is:
(A) An active drug
(B) An inactive substance ✅
(C) A reinforcement
(D) A stress response
Explanation: Placebos are inactive treatments given in research to measure psychological effects.