Week 8 · Chapter

Chapter 8 — Midterm Review & Exam

Introduction to Psychology Free sample edition

The module's primary reading · ~30–40 minutes · Objective 1 (explain what makes psychology a science and compare its major theoretical perspectives (biological, psychodynamic, behavioral, cognitive, humanistic, sociocultural)), Objective 2 (evaluate psychological research methods and ethics, distinguishing correlation from causation, random sampling from random assignment, and identifying sources of bias), Objective 3 (describe the biological bases of behavior: neurons and neural transmission, the major neurotransmitters, and the structures and functions of the nervous system and brain), Objective 4 (explain how humans sense and perceive the world and how sleep, dreaming, and psychoactive drugs shape states of consciousness), Objective 5 (compare the major models of learning and memory and apply them to everyday behavior, including why memory is reconstructive) · Read it early this week, before the review activities and well before the midterm.

In plain language

This week you look back at the first half of the course and see how it fits together. Seven weeks of psychology come down to five questions: what psychology studies, how it knows, where behavior lives, how the world gets in, and how experience changes you. You also get one new tool, the "how do we know?" checklist (three questions you ask of any claim about people). It asks what kind of study produced the claim, what that kind of study is allowed to say, and what hidden factor could explain the result. That habit is what you carry into the second half of the course.

Why you already care about this

A friend shares a post: "Students who sleep more get better grades." It sounds right. You may even want it to be true. But what would it take to know it? Would you need to watch students, or change something about them? And if sleep and grades rise together, could something else be pushing both?

You have been asking those questions for seven weeks. In Week 2 you watched Loftus and Palmer (1974) change one word in a question, from "hit" to "smashed", and change what people remembered. In Week 5 you saw ten students' sleep and quiz scores rise together, with r (the correlation coefficient) of 0.8457. One of those studies earns the word "cause." The other does not. By the end of this chapter you will know exactly why, and you will be able to say it on the midterm without hesitating.

This chapter walks the first half once more, one question at a time, using numbers the course has already pinned. Then it turns the Week 2 habit into a checklist you can run on anything.

By the end of this chapter you will be able to:

explain what psychology studies, and tell a theory from a hypothesis;
match a research design to the claim it is allowed to make, and keep random sampling apart from random assignment;
trace a message through a neuron and describe a brain chemical with "associated with" language;
tell sensation from perception, and place the sleep stages and drug families correctly;
label a classical or operant conditioning example, and explain why a confident memory can still be wrong;
run the "how do we know?" checklist on an experiment and on a correlational study, and say which claim each one earns.

Carry this sentence with you: name the design; then let the design set the claim.

Where we are

Already covered: Week 1 defined psychology as a science. Week 2 taught research designs and ethics. Week 3 traced behavior to the nervous system. Weeks 4 and 5 covered sensing, perceiving, and consciousness. Weeks 6 and 7 covered learning and memory.
This week: a review of Weeks 1 to 7 built around five questions, one new tool, the "how do we know?" checklist, and the midterm.
How they connect: the checklist is the Week 2 three-question move, made formal, and every review section ends by asking how we know its main finding.
Where we're going next: Week 9, Cognition, Language & Intelligence, opens the second half, and the checklist comes with you as you study how people think, judge, and solve problems.

Each week so far added one piece. Week 1 gave you the definition of the field and its six perspectives. Week 2 gave you the tools to check any claim: designs, variables, sampling, and ethics. Week 3 took you inside the nervous system. Week 4 followed light and sound into the brain, and Week 5 asked what happens to awareness when you sleep. Week 6 showed how experience changes behavior, and Week 7 showed how the brain keeps, loses, and rebuilds memories. The midterm covers all of it. Use the sections below as a checklist of your own: if a step feels shaky, go back to that week's chapter.

1. Ask what psychology studies: behavior, mental processes, and six lenses

Picture a light flashing on a screen and your finger pressing a key. Someone can watch your finger move. Nobody can watch you notice the light. Psychology studies both.

Psychology is the scientific study of behavior and mental processes: what people and animals observably do, and what can be inferred about how they think and feel, tested against systematically gathered evidence.
Behavior is what someone else could observe and record. Mental processes, such as noticing, remembering, and feeling, are inferred from behavior.

The field's first laboratory made that idea concrete. Wilhelm Wundt opened his laboratory at Leipzig in 1879, and his instruments timed how fast people reacted.

Worked example — the reaction-time sample. The course's nine reaction-time trials are an illustrative sample, not real data. Each value is milliseconds (ms) from a flash to a key press.

Add the trials: 312 + 289 + 401 + 356 + 298 + 275 + 388 + 342 + 310 = 2,971 ms.
Find the mean: x̄ (the mean) = 2,971 ⁄ 9 = 330.1111 ms.
Find the median: sorted, the middle value of the nine is 312 ms.
Read them together: the slow trials of 388 ms and 401 ms pull the mean above the median.

In words: a typical trial took about a third of a second, and a few slow trials made the average look slower than the middle trial.

Week 1 also gave you six lenses for one behavior: biological, psychodynamic, behavioral, cognitive, humanistic, and sociocultural. The biopsychosocial model holds them together. And it gave you two words that are easy to blur. A theory is a broad explanation already backed by evidence. A hypothesis is a specific prediction that data could prove wrong.

Misconception check — "it's only common sense." Students often think psychology tells us what we already knew. It is tempting because a finding feels obvious once you hear it. That feeling is hindsight bias, the sense that you knew it all along. Common sense explains every outcome after the fact and predicts nothing before it. The cure is evidence gathered before anyone knows the answer.

Memory hook: watch the behavior; infer the process; test the guess.

2. Ask how psychology knows: match the design to the claim

Imagine three researchers curious about phone use and sleep. One follows a single student for a month. One surveys 500 students. One randomly assigns students to phones-off or phones-on nights. All three study the same topic. Only one can say what causes what.

A descriptive study (a case study, naturalistic observation, or a survey) records what people do or say. It describes; it cannot explain why.
A correlational study measures two variables as they occur and reports r (the correlation coefficient), a number from −1 to +1. It has no IV or DV, only measured variables.
An experiment manipulates the independent variable (IV), measures the dependent variable (DV), and uses random assignment, placing people into conditions by chance, so the groups start out alike.

Two random procedures do two different jobs. Random sampling decides who gets into the study, so you can generalize to a population. Random assignment decides who gets which condition, so you can claim a cause. A good measure also has two qualities. Reliability means it gives the same result twice; validity means it measures what it claims to.

Worked example — ethics in numbers. Milgram (1963) reported that 26 of 40 participants continued to the 450-volt switch.

Turn the count into a percentage: 26 ⁄ 40 = 65%.
Ask what the participants knew: they believed the shocks were real.
Name the rules that followed: informed consent, the right to withdraw, protection from harm, debriefing after any deception, confidentiality, and approval by an Institutional Review Board (IRB) before a study begins.

In words: about two in three ordinary people went all the way, and the stress they experienced is part of why research with people now runs under strict rules.

Misconception check — two kinds of random. Students often think random sampling and random assignment are the same thing. It is tempting because both use the word "random." But random sampling picks who is studied, and it supports generalizing. Random assignment picks who gets which condition, and it supports a cause. A study can have either one without the other.

Memory hook: sampling is about who; assignment is about what causes what.

3. Ask where behavior lives: neurons, chemicals, and brain structures

Touch a hot pan handle and your hand jerks back before you decide anything. That speed comes from cells built to carry messages.

A neuron, a nerve cell, receives signals at its dendrites, combines them in the soma, and sends an impulse down its axon, sped by the myelin sheath, to the terminal buttons.
At rest, a neuron sits at about −70 mV. Once input crosses threshold, it fires an all-or-none action potential.
Neurotransmitters cross the synapse, and reuptake clears the gap.

Worked example — a hotter pan. You touch a warm handle, then a very hot one.

Resting state: the sensory neuron starts at about −70 mV.
Warm handle: the input crosses threshold, and the neuron fires.
Very hot handle: each action potential is the same size as before. What changes is the rate. The neuron fires more often each second.

In words: a stronger stimulus makes a neuron fire more often, never bigger.

Week 3 also mapped the larger system. The sympathetic division mobilizes you for fight-or-flight; the parasympathetic division calms you afterward. The hippocampus is needed to form new declarative memories. The case of H.M. (Scoville & Milner, 1957) showed it: after much of both hippocampi was removed, he could not form new declarative memories but kept most older ones. That was a case study, so it suggested a link that later research tested.

Misconception check — "serotonin causes depression." Students often describe a brain chemical as the cause of a mood. It is tempting because headlines say it that way. But the evidence supports "associated with," not "causes." Serotonin is associated with mood, sleep, and appetite. Dopamine is associated with reward, movement, and learning. Write "associated with" every time.

Memory hook: all or none for each spike; more spikes for a stronger touch.

4. Ask how the world gets in: sensing, perceiving, and sleeping

Stand on a dark road and spot a faint light on a distant hill. Your eye has to detect it. Your brain has to decide what it is. Those are two different jobs.

Sensation is receptors detecting physical energy and turning it into neural signals. Perception is the brain organizing and interpreting those signals.
The absolute threshold is the weakest stimulus a person detects 50% of the time. The difference threshold is the smallest change detected 50% of the time.

Worked example — two classic thresholds. Galanter (1962) gave two illustrations of the absolute threshold.

Vision: on a clear, dark night, a person can detect a candle flame about 30 miles away.
Hearing: in a quiet room, a person can detect a clock ticking about 20 feet away.
Classify each one: both go from nothing to something, so both are absolute thresholds. Noticing that a second candle has been lit is a change, so that would be a difference threshold.

In words: your senses are more sensitive than most people guess, and the edge of sensing is a measurement taken over many tries.

Week 5 turned to awareness itself. Your circadian rhythm runs about 24 hours. The first REM period comes about 90 minutes after you fall asleep, and the cycle repeats through the night. Most adults need about 7 to 9 hours a night. Drugs fall into three families: depressants slow the nervous system, stimulants speed it up, and hallucinogens distort perception.

Misconception check — the deepest sleep. Students often say REM is the deepest sleep. It is tempting because REM brings the most vivid dreams. But NREM-3, slow-wave sleep, is the deepest stage. REM is the most brain-active stage, with brain activity much like waking. A second trap from the same week: alcohol is a depressant, whatever the first half hour feels like.

Memory hook: senses detect, the brain decides, and sleep is busy, not off.

5. Ask how experience changes you: learning and memory

A dog that drools at the sound of a can opener has learned something. So has a student who remembers a locker code from last year but not this year's. Weeks 6 and 7 explained both.

In classical conditioning, a neutral signal paired with an unconditioned stimulus (UCS), which triggers an unconditioned response (UCR), becomes a conditioned stimulus (CS) that triggers a conditioned response (CR).
In operant conditioning, consequences change voluntary behavior. Positive means add and negative means remove. Reinforcement increases a behavior; punishment decreases it.
In observational learning, you learn by watching. Bandura (1961) showed children copying an adult who attacked a Bobo doll.

Worked example — label two kitchen and homework moments. Each moment gets its labels in order.

Classical: food makes a dog drool with no learning, so food is the UCS and drooling is the UCR. After the can opener's whir is paired with food, the whir alone (the CS) brings drooling (the CR). In order: UCS → UCR, then CS → CR.
Operant: a parent takes away a chore after a teen finishes an assignment early. Something is removed, so it is negative. The early finishing increases, so it is reinforcement. Together: negative reinforcement.

Memory runs as three processes in order: encoding, storage, retrieval. Short-term memory is small and brief.

Worked example — how much and how long. Each number below is pinned from Week 7.

Capacity: Miller (1956) put short-term memory at 7 ± 2 items, so from 7 − 2 = 5 to 7 + 2 = 9 items. Cowan (2010) revised working memory to about 4 ± 1 chunks, from 4 − 1 = 3 to 4 + 1 = 5.
Duration: Peterson and Peterson (1959) found recall of about 80% after 3 seconds, but only about 10% after 18 seconds, when counting backward blocked rehearsal.
Long-term forgetting: Ebbinghaus (1885) measured percent savings of 58.2% at 19 minutes and 21.1% at 31 days. That is a drop of 58.2 − 21.1 = 37.1 percentage points, and 58.2 − 44.2 = 14.0 of those points went in the first hour.

In words: you lose most of an unrehearsed item within seconds, and the forgetting curve drops steeply before it levels off.

Memory is also rebuilt, not replayed. In Week 7, a single verb in a question changed what witnesses later remembered. Confidence is not accuracy.

Misconception check — negative reinforcement is not punishment. Students often call negative reinforcement a punishment. It is tempting because "negative" sounds bad. But negative means remove, and reinforcement means the behavior increases. Removing the chore made early finishing more likely, so it reinforced it. Punishment always makes a behavior less likely.

Memory hook: add or remove; then ask whether the behavior went up or down.

6. Build the checklist and run it on an experiment

Now the new idea. Every section above ended with a finding. Every finding came from a study. And every study can only claim as much as its design allows. In Week 2 you met this as a three-question move. Now it becomes a checklist you run on every claim, every time.

The "how do we know?" checklist is a three-step test for any claim about people: name the design that produced it, say what that design is allowed to conclude, and name a third variable that could explain the result.
A causal claim is a statement that one variable changes another, such as "the wording changed the estimates"; only an experiment with random assignment earns it.

Run it first on the eyewitness experiment the course keeps returning to. The table lists the mean speed estimate for each verb in Experiment 1.

Loftus and Palmer (1974), Experiment 1: mean speed estimate by verb, in miles per hour (45 students)
Verb in the question	Mean estimate (mph)
smashed	40.8
collided	39.3
bumped	38.1
hit	34.0
contacted	31.8

Worked example — the checklist on Loftus and Palmer (1974). You take the three steps in order.

Step 1, the design. The researchers manipulated the verb in the question, so the verb is the IV. They measured the speed estimate in mph, so that is the DV. You have an experiment.
Step 1, the numbers. In Experiment 1, with n (the number of students) of 45, "smashed" averaged 40.8 mph and "contacted" averaged 31.8 mph. The gap is 40.8 − 31.8 = 9.0 mph.
Step 1, the memory test. In Experiment 2, a week later, 16 ⁄ 50 = 32% of the "smashed" group reported broken glass that was never there. Only 7 ⁄ 50 = 14% of the "hit" group did, and 6 ⁄ 50 = 12% of the control group asked no speed question. That is 32 − 14 = 18 points more for "smashed" than for "hit".
Step 2, the allowed claim. Participants were randomly assigned to a verb, so the verb is the only planned difference between the groups. You may make a causal claim: the wording changed the estimates and the memory reports.
Step 3, the third variable. Driving experience or eyesight could change a speed estimate. Random assignment spreads those differences across the groups by chance, so no third variable is likely to explain the gap.

In words: about one in three students who heard "smashed" remembered glass that was never there, versus about one in seven who heard "hit", more than twice the rate, and the design lets you say the word did it.

Honesty note: the checklist also tells you what an experiment does not settle. The participants were students watching films of accidents. Whether the same effect holds for every witness at a real crash is a question about sampling, not about cause.

Misconception check — "an experiment proves it for everyone." Students often think a good experiment settles a question for all people everywhere. It is tempting because the word "cause" sounds final. But random assignment earns the cause inside the study. Random sampling decides how far the result reaches beyond it. Keep the two jobs apart, as Week 2 taught.

Memory hook: assigned at random, not only measured? Then say "cause."

7. Run the checklist on a correlation: sleep and quiz scores

Now back to the post your friend shared. The course has a small dataset that matches it. Ten students reported their hours of sleep the night before a 20-point quiz, along with their scores. It is illustrative, constructed for this course, not real data.

Hours of sleep and next-day quiz score (out of 20) for ten students, an illustrative dataset
Hours of sleep	5	6	6.5	7	7	7.5	8	8	8.5	9
Quiz score	11	14	12	15	13	16	17	14	18	17

An association claim is a statement that two measured variables tend to move together, such as "students who slept more tended to score higher", without saying that either one changes the other.

Worked example — the checklist on the sleep data. You take the same three steps.

Step 1, the design. Here n (the number of students) is 10. Nobody's sleep was changed; it was only measured. So it is a correlational study, with no IV or DV.
Step 1, the numbers. Mean sleep is 7.25 hours and mean score is 14.7 points. The correlation is r (the correlation coefficient) = 0.8457.
Step 2, the allowed claim. The sign is positive, so sleep and score rise together. The size, 0.8457, is close to +1, so the linear association is strong. In this sample, students who slept more tended to score higher. You may make an association claim. Nothing stronger fits.
Step 3, the third variable. A student who slept more may also have finished studying earlier, had a lighter work schedule, or felt less anxious. Any of those could raise both sleep and score. The arrow could also run the other way: a good study day may have made sleep easier.

In words: the pattern is strong, but it is a pattern, not a proof. Only an experiment could test sleep as a cause, and it would need to randomly assign how long students slept.

Put the two studies side by side. Loftus and Palmer manipulated one thing and assigned people at random, so they earned "cause." The sleep data measured two things and assigned nothing, so they earned "associated with." The numbers do not decide which claim you may make. The design does.

Caveat: a strong r is still not a cause. Even an r near +1 can come from a third variable, and r is never a percentage.

Misconception check — "a strong correlation proves it." Students often think a big r, like 0.8457, is strong enough to call sleep the cause. It is tempting because the pattern looks so tidy. But strength is not design. A correlation of any size leaves the third-variable problem and the directionality problem open. Only random assignment closes them.

Pause and think. Choose one and answer it in a sentence or two:

(a) Think of a health or wellness claim you have seen online, and run the three checklist steps on it: design, allowed claim, third variable.
(b) Think of a claim a friend or relative made about why people act the way they do, and say what study design would be needed to earn a causal claim about it.

Memory hook: a correlation earns "associated with"; only random assignment earns "cause."

Key terms

"how do we know?" checklist — A three-step test for any claim about people: name the design that produced it, say what that design is allowed to conclude, and name a third variable that could explain the result. (first used: 6. Build the checklist and run it on an experiment)
causal claim — A statement that one variable changes another, such as "the wording changed the estimates"; only an experiment with random assignment earns it. (first used: 6. Build the checklist and run it on an experiment)
association claim — A statement that two measured variables tend to move together, such as "students who slept more tended to score higher", without saying that either one changes the other. (first used: 7. Run the checklist on a correlation: sleep and quiz scores)

Summary

Psychology studies behavior, which you observe, and mental processes, which you infer.
Descriptive studies describe, correlational studies find associations, and only experiments with random assignment show causes.
Random sampling supports generalizing; random assignment supports a cause.
A neuron fires all or none, and brain chemicals are associated with functions, not single causes of moods.
Sensation detects and perception constructs; NREM-3 is the deepest sleep and REM the most brain-active.
Positive means add and negative means remove; reinforcement raises a behavior and punishment lowers it.
Memory runs encoding, storage, retrieval, and it is rebuilt, so confidence is not accuracy.
The "how do we know?" checklist asks for the design, the allowed claim, and a third variable, every time.

Check your understanding

Work these before looking at the answers — they are ungraded, and the answers (with reasoning) are at the bottom of the page.

A news story reports that people who own a dog visit the doctor less often. Run the "how do we know?" checklist on it: what design is likely, what claim does it earn, and what third variable could explain it?
A bakery owner randomly assigns 60 customers to see a menu with photos and 60 to see the same menu without photos. 18 of the photo group and 9 of the no-photo group order dessert. Name the IV and the DV, find each group's percentage, and say what claim the design earns.
Every time Amara's phone chimes, a message from her best friend follows, and now the chime alone makes her smile. Label the UCS, UCR, CS, and CR.
Diego learns the new code for his gym locker, and now he cannot recall the code he used last year. Which kind of interference is this, and why?

Answers (worked reasoning — read after attempting)

The researchers most likely measured dog ownership and doctor visits as they occurred, so the design is correlational. It earns an association claim: in that sample, dog owners tended to visit the doctor less. A third variable could explain it. People who are already healthier may be more able to care for a dog, so health could drive both. The arrow could also run backward: being well may make owning a dog easier.
The menu type is the IV, because the owner manipulated it. Ordering dessert is the DV, because it was measured. The photo group: 18 ⁄ 60 = 30%. The no-photo group: 9 ⁄ 60 = 15%. That is 30 − 15 = 15 points more for photos, twice the rate. Customers were randomly assigned, so the design earns a causal claim for these customers: the photos raised dessert orders. Whether it holds at other bakeries is a sampling question.
The message from her friend makes her smile with no learning, so the message is the UCS and the smile it brings is the UCR. The chime was neutral at first. After pairing, the chime is the CS, and the smile at the chime alone is the CR.
This is retroactive interference: new learning (this year's code) gets in the way of old learning (last year's code). If the old code kept popping up and blocking the new one, that would be proactive interference instead.

Next up in this module: the lecture, the slide deck, the Readings & Resources page, the practice set, the discussion, and the midterm — and next week the checklist meets the heuristics model of judgment, the mental shortcuts people use to decide.

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