Credit Sprint / Study guides / Psychology Unit 1

Credit Sprint's Guide to AP® Psychology, Unit 1: Biological Bases of Behavior

Unit 1 starts with how psychologists know what they know (methods, statistics, ethics) and then moves to the body: neurons, the brain, hormones, genes, the senses, perception, sleep and drugs. Almost every free-response question uses research methods, so this unit pays off all year.

What you need to know

• Psychology is the scientific study of behavior and mental processes. Major approaches include biological, behavioral, cognitive, humanistic, psychodynamic, sociocultural and evolutionary. Each asks a different kind of question about the same behavior.
• An experiment manipulates an independent variable (IV), measures a dependent variable (DV), uses random assignment to build equivalent groups, and is the only method that can support a cause-and-effect claim. Correlation shows that two variables are related, from -1.00 to +1.00, and never proves causation. Surveys, naturalistic observation and case studies describe behavior but cannot show cause.
• Validity asks whether a test measures what it claims to measure. Reliability asks whether it gives consistent results. A test can be reliable without being valid. Sampling bias, experimenter bias, the placebo effect and demand characteristics threaten results, and double-blind procedures and operational definitions reduce those problems.
• Descriptive statistics summarize data: mean, median, mode, range and standard deviation. In a normal curve about 68% of scores fall within 1 SD of the mean and about 95% within 2 SD. Inferential statistics ask whether a result is statistically significant, usually when p is below .05, meaning chance alone is an unlikely explanation. Ethics rules include informed consent, confidentiality, debriefing, protection from harm and approval by an institutional review board (IRB).
• A neuron has dendrites (receive signals), a cell body, an axon (sends signals) and terminal buttons that release neurotransmitters across the synapse. Myelin speeds up the signal. A neuron fires in an all-or-none action potential when its threshold is reached. Key neurotransmitters include dopamine (reward, movement), serotonin (mood, sleep), acetylcholine (muscles, memory), GABA (inhibition), glutamate (excitation) and endorphins (pain relief).
• The nervous system splits into the central (brain and spinal cord) and peripheral systems. The somatic system controls voluntary muscles. The autonomic system has a sympathetic branch (fight or flight) and a parasympathetic branch (rest and digest). The endocrine system sends hormones through the blood, with the pituitary as the master gland. Brain structures include the brainstem and medulla (breathing, heartbeat), cerebellum (balance, coordination), thalamus (sensory relay), hypothalamus (hunger, thirst, temperature), hippocampus (forming new memories), amygdala (fear and aggression) and the four cortical lobes: frontal, parietal, temporal and occipital.
• Genes and environment work together. Twin and adoption studies estimate heritability, and epigenetics shows that experience can switch genes on or off. Sensation is detecting stimuli (transduction turns energy into neural signals), and perception is organizing and interpreting them. Know absolute thresholds, signal detection, the Weber-Fechner law of just noticeable difference, sensory adaptation, top-down versus bottom-up processing, depth cues and Gestalt principles. Sleep runs in 90-minute cycles through NREM stages 1 to 3 and REM, and psychoactive drugs are depressants, stimulants, hallucinogens or opioids.

Exam traps

Key terms

• Independent variable: The factor a researcher deliberately changes or manipulates to see its effect.
• Dependent variable: The outcome a researcher measures to see whether it changes because of the independent variable.
• Random assignment: Placing participants into experimental or control groups by chance, so the groups start out equivalent.
• Random sampling: Choosing participants so that everyone in the population has an equal chance of being selected, which supports generalizing results.
• Experimental group: The group that receives the treatment or the level of the independent variable being tested.
• Control group: The comparison group that does not receive the treatment, which shows what happens without it.
• Operational definition: A precise statement of how a variable will be measured or manipulated in a specific study.
• Placebo effect: Improvement caused by a person's expectation of treatment rather than by the treatment itself.
• Double-blind procedure: A design in which neither participants nor researchers know who is in the treatment or control group.
• Confounding variable: An outside factor that varies along with the independent variable and could explain the results.
• Correlation coefficient: A number from -1.00 to +1.00 that shows the direction and strength of a relationship between two variables.
• Naturalistic observation: Watching and recording behavior in its natural setting without interfering.
• Case study: An in-depth look at one individual or small group, useful for rare cases but hard to generalize.
• Standard deviation: A measure of how spread out scores are around the mean.
• Statistical significance: A result unlikely to be due to chance alone, usually when p is less than .05.
• Informed consent: Participants agree to take part after being told what the study involves and any risks.

Practice questions

Five of the 151 Unit 1 questions in Credit Sprint. Every choice is explained in the app.