Lecture: Midterm Review & Exam
Lecture script · about 15–20 minutes spoken · Week 8
Opening
Here's a post a friend might share with you: "Students who sleep more get better grades." It sounds right. You might even hope it's true. But I want you to ask the question this course has asked every single week. How do we know?
That question isn't only for psychology majors. A nursing student weighing a new bedside routine asks it. A business major reading that a training program raised sales asks it. A parent reading a headline about screen time asks it. Each one needs to know what kind of study produced the claim, and how much that study is allowed to say.
This is Week 8, the middle of the course, and the week of the midterm. So this lecture does two jobs. First, I'll walk you back through Weeks 1 to 7 as five questions. What does psychology study? How does it know? Where does behavior live? How does the world get in? And how does experience change you, and how do you keep it? Then I'll give you one new tool, the "how do we know?" checklist, and we'll run it on two studies you already know. After that, in Week 9, Cognition, Language & Intelligence, the checklist comes with you into the second half of the course.
1. What psychology studies
Let's start where the course started. Picture a light flashing on a screen, and your finger pressing a key. Someone across the room can watch your finger move. Nobody can watch you notice the light. Psychology studies both of those things.
That's the definition from Week 1. 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. The finger press is behavior. Noticing the light is a mental process, and you infer it from the behavior.
The field's first laboratory turned that idea into measurement. Wilhelm Wundt opened his laboratory at Leipzig in 1879, and his instruments timed how fast people reacted. Our course has a small reaction-time sample of nine trials, made up for teaching, not real data. Its median, the middle trial, is 312 milliseconds. Its mean, the average, is about 330 milliseconds. The mean sits above the median because two slow trials, 388 and 401 milliseconds, pull it up.
Week 1 also gave you six lenses for looking at one behavior: biological, psychodynamic, behavioral, cognitive, humanistic, and sociocultural. And it gave you two words people blur all the time. A theory is a broad explanation already backed by evidence. A hypothesis is a specific prediction that data could prove wrong.
Here's the trap to avoid. People often say psychology only tells us what common sense already knew. That feeling has a name: hindsight bias, the sense that you knew it all along. Common sense explains every outcome after the fact. It predicts nothing before it.
Pause and try this. "Students who sleep 7 hours or more will score higher on the next quiz than students who sleep less." Is that a theory or a hypothesis?
Decide before you read on.
Here's the answer. It's a hypothesis. It makes one specific prediction that data could prove wrong, which is exactly what a theory, a broad, evidence-backed explanation, doesn't do on its own.
2. How psychology knows
Now imagine three researchers who all want to study phone use and sleep. One follows a single student closely for a month. One surveys a large group of students. One randomly assigns students to phones-off nights or phones-on nights. Same topic, three designs. Only one of them can say what causes what.
Week 2 gave you the three designs. A descriptive study, like a case study, an observation, or a survey, records what people do or say. It describes, and it can't explain why. A correlational study measures two variables as they occur and reports r, the correlation coefficient, a number from negative 1 to positive 1. It has no independent or dependent variable, only measured ones. An experiment manipulates the independent variable, measures the dependent variable, and uses random assignment, placing people into conditions by chance, so the groups start out alike.
Two random procedures do two different jobs, and the midterm will check that you keep them apart. 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 measure needs two qualities too. Reliability means it gives the same result twice. Validity means it measures what it claims to.
Week 2 also asked how people in studies should be treated. Milgram reported in 1963 that 26 of 40 participants, which is 65 percent, continued to the 450-volt switch. They believed the shocks were real. That stress is part of why research now requires informed consent, the right to withdraw, debriefing after any deception, and approval by an Institutional Review Board before a study begins.
Pause and try this. A researcher picks names by lottery from the full list of students on a campus, then lets each chosen student decide which condition to join. Which random procedure did the study use, and which one did it skip?
Take a moment and name both.
Here's the answer. It used random sampling, because the lottery decided who got into the study. It skipped random assignment, because the students chose their own condition, so the study can't claim a cause.
3. Where behavior lives
Picture touching a hot pan handle. Your hand jerks back before you've decided anything. That speed comes from cells built to carry messages.
A neuron, a nerve cell, receives signals at its dendrites, combines them in the cell body, and sends an impulse down its axon to the terminal buttons. At rest, a neuron sits at about negative 70 millivolts. Once its input crosses threshold, it fires an action potential, and that impulse is all or none. It happens at full strength or not at all.
Here's what that means for the pan. A warm handle pushes the neuron past threshold, and it fires. A very hot handle doesn't make bigger impulses. It makes more of them each second. The size stays the same; the rate goes up.
When the impulse reaches the end of the axon, chemical messengers called neurotransmitters cross the synapse to the next cell. Be careful how you talk about them. Serotonin is associated with mood, sleep, and appetite. Dopamine is associated with reward, movement, and learning. "Associated with" is the honest phrase. A chemical is never the single cause of a mood.
Week 3 also mapped the bigger system. The sympathetic division gets your body ready for fight-or-flight. The parasympathetic division calms it afterward. And the hippocampus is needed to form new memories of facts and events. The case of H.M., reported by Scoville and Milner in 1957, showed that. After much of both hippocampi was removed, he could not form new declarative memories, but he kept most older ones.
Pause and try this. A friend says, "Turn the stimulus up and each action potential gets bigger." What's wrong with that sentence?
Think about the rule before you read the answer.
Here's the answer. The action potential is all or none, so its size never changes. A stronger stimulus makes the neuron fire more often each second instead.
4. How the world gets in
Imagine standing on a dark road far from town. You spot one faint light on a distant hill. Your eye has to detect it, and your brain has to decide what it is. Those are two different jobs.
Week 4 named them. Sensation is your receptors detecting physical energy and turning it into neural signals. Perception is your brain organizing and interpreting those signals. Your senses detect; your brain decides.
Psychologists measure the edge of sensing. The absolute threshold is the weakest stimulus a person detects 50 percent of the time. Galanter described two classic examples in 1962. On a clear, dark night, a person can detect a candle flame about 30 miles away. In a quiet room, a person can detect a clock ticking about 20 feet away. The difference threshold is a different measurement. It's the smallest change a person detects 50 percent of the time.
Week 5 turned to awareness itself, and to sleep. Your circadian rhythm, your body clock, 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. And drugs fall into three families. Depressants slow the nervous system, stimulants speed it up, and hallucinogens distort perception.
Two traps live here. People call REM the deepest sleep, because it brings the most vivid dreams. It isn't. The third stage of non-REM sleep, slow-wave sleep, is the deepest. REM is the most brain-active stage. And alcohol is a depressant, whatever the first half hour feels like.
Pause and try this. You're in a quiet room and you first notice a clock's tick when it's about 20 feet away. Then someone sets a second clock beside the first, and you notice the sound got louder. Which threshold does each moment show?
Sort the two moments before you read on.
Here's the answer. The first moment is the absolute threshold, because the sound went from nothing to something. The second is the difference threshold, because you noticed a change in a sound that was already there.
5. How experience changes you, and how you keep it
Here's a story you may know from a kitchen. A dog drools when food appears. Nobody taught it that. But every time someone opens a can of food, the can opener whirs first. After enough pairings, the dog drools at the whir alone, before any food is in sight.
That's classical conditioning, from Week 6. The food is the unconditioned stimulus, the UCS, because it triggers drooling with no learning. Drooling at food is the unconditioned response, the UCR. The whir becomes the conditioned stimulus, the CS. And drooling at the whir alone is the conditioned response, the CR.
Operant conditioning is about consequences. Positive means add, and negative means remove. Reinforcement makes a behavior more likely, and punishment makes it less likely. So if a parent takes away a chore after a teen finishes an assignment early, something was removed, and early finishing goes up. That's negative reinforcement, not punishment. And Bandura showed in 1961 that children learn by watching, too.
Week 7 took up memory. It runs as three processes in order: encoding, storage, retrieval. Short-term memory is small. Miller put it at 7 plus or minus 2 items in 1956, and Cowan revised working memory in 2010 to about 4 plus or minus 1 chunks. It's also brief. Peterson and Peterson found in 1959 that people recalled about 80 percent after 3 seconds, but only about 10 percent after 18 seconds, when counting backward blocked rehearsal. Over longer spans, Ebbinghaus's forgetting curve from 1885 drops steeply and then levels off: savings of 58.2 percent at 19 minutes, down to 21.1 percent at 31 days.
And memory is rebuilt, not replayed. A single word in a question changed what witnesses remembered. Confidence is not accuracy.
Pause and try this. A student's alarm stops its loud buzz the moment the student gets out of bed, and getting up quickly becomes more common. Is that negative reinforcement or punishment?
Ask two questions: added or removed, and up or down?
Here's the answer. It's negative reinforcement. The buzz is removed, which is the negative part, and the behavior goes up, which is the reinforcement part.
6. The "how do we know?" checklist, on an experiment
Now the new idea. Every section so far ended on a finding, and every finding came from a study. In Week 2 you met a three-question move for headlines. Here 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. Design, claim, third variable.
Let's run it on Loftus and Palmer, 1974. Students watched films of car accidents and were asked how fast the cars were going when they "smashed" or "hit" or "contacted" each other. Step one, the design. The researchers manipulated the verb, so the verb is the independent variable. They measured the speed estimate in miles per hour, so that's the dependent variable. That's an experiment. And the numbers: "smashed" averaged 40.8 miles per hour, and "contacted" averaged 31.8. That's a gap of 9.0 miles per hour from one word.
A week later came the memory test. 32 percent of the "smashed" group reported broken glass that was never in the film. Only 14 percent of the "hit" group did, and 12 percent of a control group that heard no speed question.
Step two, the claim. People were randomly assigned to a verb, so the verb was the only planned difference between the groups. That earns a causal claim, a statement that one variable changes another. The wording changed the estimates and the memory reports.
Step three, the third variable. Driving experience or eyesight could change a speed guess. But random assignment spreads those differences across the groups by chance, so none of them is likely to explain the gap. What stays open is how far it reaches. These were students watching films, and generalizing to every real witness is a sampling question, not a question about cause.
Pause and try this. Which single feature of the Loftus and Palmer design lets you rule out driving experience as the explanation?
Name the feature before you read on.
Here's the answer. Random assignment. Because chance decided who heard which verb, experienced and new drivers ended up spread across the groups, so experience is very unlikely to explain why "smashed" got higher estimates.
7. The checklist on a correlation
Back to the post from the opening. The course has a small dataset that matches it. Ten students, made up for teaching, reported their hours of sleep the night before a 20-point quiz, along with their scores.
Step one, the design. Nobody's sleep was changed. It was only measured. So it's a correlational study, with no independent or dependent variable. Mean sleep is 7.25 hours, and the mean score is 14.7 points. The correlation, r, is 0.8457.
Step two, the claim. The sign is positive, so sleep and score rise together. The size, 0.8457, is close to positive 1, so the association is strong. In this sample, students who slept more tended to score higher. That's an association claim, a statement that two measured variables tend to move together, without saying either one changes the other. Nothing stronger fits.
Step three, 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. And the arrow could run the other way: a good study day might have made sleep easier.
So put the two studies side by side. Loftus and Palmer changed one thing and assigned people at random, so they earned "cause." The sleep study measured two things and assigned nothing, so it earned "associated with." The numbers didn't decide that. The design did.
Pause and try this. Someone says, "An r of 0.8457 is so strong that sleep must cause higher scores." Which step of the checklist does that skip?
Find the missing step before you read on.
Here's the answer. It skips step two. The design is correlational, so it earns only an association claim, and a strong r can't close the third-variable problem. Only an experiment that randomly assigned sleep could test it as a cause.
Closing
Let's pull it together in the order we took it. Psychology studies behavior, which you observe, and mental processes, which you infer. Each research design earns its own claim, and random sampling and random assignment do different jobs. A neuron fires all or none, and brain chemicals are associated with functions, not single causes. Sensation detects and perception decides, and REM is the most brain-active stage, not the deepest. Positive means add and negative means remove, and memory is rebuilt, so confidence isn't accuracy. Finally, the checklist: design, claim, third variable. An experiment with random assignment earns "cause." A correlation earns "associated with."
Next in this module come the slide deck, the Readings & Resources page, the practice set, and the discussion, and then the midterm. After that, in Week 9, Cognition, Language & Intelligence, you'll carry the checklist into how people think, judge, and solve problems.
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