Lecture: The Science of Psychology
Lecture script · about 15–20 minutes spoken · Week 1
Opening
Think about the last time someone surprised you. Maybe a friend went quiet in a group chat, or a coworker who never helps suddenly stayed late to help you. You probably had an explanation ready within seconds. Everyone does. We all carry around a private theory of why people do what they do. This course asks you to hold those explanations up to the light and ask one question: how would anyone know?
That question matters wherever people are. A nursing student reads a worried face. A business major wonders why customers buy one thing and not another. A future teacher wonders why a capable student stalls. All of them are making claims about people, and all of them can be right or wrong.
This is the first week of the course, so we start at the foundation. In this lecture I'll do six things. I'll define what psychology studies. I'll take you into the first psychology laboratory and show you what it measured. I'll walk through the field's history in six moves. I'll show you six ways to explain one behavior. Then I'll show you why common sense isn't enough, and how a theory differs from a hypothesis. Next week, in Week 2, we'll turn all of this into research methods you can use.
1. Behavior and mental processes
Picture a classmate in the front row. You can see her tap her pen, glance at the clock, and pack her bag a little early. What you can't see is the worry about getting to work on time. You can only guess at it from what she does. Hold on to that split, because the whole field is built on it.
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.
Each half of that definition has its own name. Behavior is anything a person or animal does that someone else could observe and record, such as speaking, pressing a key, or walking away. Mental processes are the inner experiences that cannot be watched directly, such as thinking, remembering, feeling, and perceiving, which psychologists infer from behavior.
Here's the move that makes psychology a science. You can't measure a thought directly. But you can measure what a thought makes a person do. Imagine you're sitting in front of a lamp with one finger resting on a key. When the lamp flashes, you press the key as fast as you can. The press is behavior. Anyone in the room can see it, and a clock can record when it happened. Noticing the flash and deciding to move is a mental process. Nobody can see that part. But the gap between the flash and the press tells us something about it.
That gap has a name. Reaction time is the time, measured in milliseconds, between a signal such as a flash of light and a person's response to it, such as a key press. A longer gap suggests more mental work happened between seeing and doing.
Pause and try this. A shopper picks up a jacket, frowns, and puts it back. Which part is behavior, and which part is a mental process?
Give yourself a moment before the answer.
Here's the answer. Picking up the jacket, frowning, and putting it back are all behavior, because anyone nearby could see them. Deciding the jacket costs too much is the mental process, which you can only infer from what she did.
So when you hear the word psychology, think of two layers. There's what people do, and there's what we infer is happening inside them.
2. The first laboratory
Now let's go to Leipzig, in Germany, in 1879. That year, Wilhelm Wundt opened a laboratory for experimental psychology. It's the usual birth date given for psychology as an experimental science.
Two kinds of work happened in that room. The first was called introspection. Introspection is the method of Wundt's laboratory in which trained observers looked inward and reported the parts of their own conscious experience under controlled conditions. An observer might hear a single tone and describe each sensation it produced. The second kind of work used instruments that timed reactions. That's the work that lasted, because it left numbers behind.
Let me show you what those numbers look like. I'll use a reaction-time sample built for this course. It's illustrative, not real data. There are nine trials, and in each one a light flashes and a person presses a key. Here are the times in milliseconds: 312, 289, 401, 356, 298, 275, 388, 342, and 310. A millisecond is a thousandth of a second. So 1 second is 1,000 milliseconds, and a 312 millisecond trial takes about a third of a second.
Nine numbers are hard to hold in your head, so we summarize them. The mean is the sum of a set of values divided by how many values there are; it is pulled toward a few unusually large or small values. Add the nine trials and you get 2,971 milliseconds. Divide by 9 and the mean is 330.1111 milliseconds, a little over 330.
The median is the middle value of a set once the values are sorted from smallest to largest; a few unusually large or small values barely move it. Sort the nine trials from fastest to slowest and count to the 5th one. That middle trial is 312 milliseconds.
The range is the largest value minus the smallest value in a set, which tells how far the values stretch from one end to the other. The slowest trial is 401 and the fastest is 275, so the range is 126 milliseconds.
Pause and try this. The mean is about 330 milliseconds and the median is 312. Which one sits higher, and what pulled it there?
Think about the two slowest trials before you answer.
Here's the answer. The mean sits higher. The two slow trials, 388 and 401 milliseconds, pull the mean up, while the median stays with the typical trial. That makes the median the better picture of a typical trial in this sample.
There's an honest lesson in this laboratory too. Introspection didn't last as a scientific method. Two trained observers could describe the same tone in different words, and nobody could check who was right. A timed reaction gives everyone the same number to argue about.
3. The history in six moves
Here's an image to help you hold the history. Imagine six people walking into the same room and asking what the mind is. One asks what it's made of. One asks what it's for. One asks what it hides. One says to stop guessing and watch what people do. One asks what people could become. One asks how the mind handles information. That room is the history of psychology.
The first move is Wundt's laboratory, which you've already met. The second move is a split. Edward Titchener trained under Wundt and carried the work forward. Structuralism is an early school of psychology, built by Edward Titchener, that tried to break conscious experience into its basic elements through introspection. Functionalism is an early school of psychology, led by William James, that asked what mental processes are for: how they help an organism adapt to its surroundings. Think of a bicycle. A structuralist lists its parts. A functionalist asks what it does for its rider.
The third move is Sigmund Freud, who lived from 1856 to 1939. Psychoanalysis is Sigmund Freud's approach, which holds that wishes and conflicts outside a person's awareness shape behavior, and which treats people by bringing those conflicts into awareness.
The fourth move pushed hard the other way. In a 1913 paper, John B. Watson argued that psychology should study only what can be observed, and B. F. Skinner later extended the idea. Behaviorism is the school, led by John B. Watson and later B. F. Skinner, that limited psychology to observable behavior and the consequences that shape it.
The fifth move is the humanistic movement, the movement led by Abraham Maslow and Carl Rogers that centered psychology on personal growth, free choice, and each person's own point of view.
The sixth move brought the mind back. Ulric Neisser's 1967 book, Cognitive Psychology, named and helped launch the cognitive era, the study of how people notice, remember, and solve problems. Alongside it, better tools for studying the brain and body drew more researchers toward biology.
Pause and try this. Someone asks, "What does memory do to help a person adapt?" Which school asked that kind of question, and who led it?
Settle on your answer before you read on.
Here's the answer. That's functionalism, led by William James. The question asks what a mental process is for, and asking what something is for is the functionalist move.
One warning before we leave the history. People, and chatbots, sometimes call Freud the founder of scientific psychology, or give functionalism to Wundt. Neither is right. Wundt's 1879 laboratory marks the start of experimental psychology, and James led functionalism.
4. Six perspectives on one behavior
It's 10 at night, there's a paper due in the morning, and you've written one sentence. You told yourself last week you'd start early. Why didn't you? If you asked six psychologists, you'd get six different answers, and here's the surprise: they could all be partly right.
Each answer comes from a perspective, one of the main angles from which psychologists explain behavior, each asking its own kind of question about the same event. There are six.
The biological perspective explains behavior through the brain, the body, hormones, and genes. Through that lens, sleep loss and stress hormones may change how the body handles the deadline. The psychodynamic perspective, grown from Freud's psychoanalysis, explains behavior through feelings, conflicts, and motives a person may not be aware of. Through that lens, the paper may stir an unspoken fear of being judged. The behavioral perspective explains behavior through learning: the rewards and consequences that have followed similar behavior in the past. Through that lens, past last-minute papers that still earned a passing grade rewarded the habit.
The cognitive perspective explains behavior through how a person thinks: what the person notices, expects, remembers, and believes. Through that lens, the student expects to write faster under pressure and misjudges the time it takes. The humanistic perspective explains behavior through a person's growth, choices, and sense of who they want to become. Through that lens, the assignment feels disconnected from what the student wants to become. And the sociocultural perspective explains behavior through other people, groups, and culture: the norms and expectations a person lives among. Through that lens, friends who all start late make starting late feel normal.
Notice that none of those cancels the others. That's why psychologists talk about levels of analysis, the biological, psychological, and social layers at which any one behavior can be explained, from the body up to the culture around a person. The biopsychosocial model is the view that biological, psychological, and social influences act together on behavior and health, so a full explanation uses all three levels of analysis. G. L. Engel proposed it in 1977.
Pause and try this. A friend says, "Everyone in my apartment snacks while we watch shows, so I do too." Which perspective is that explanation using?
Picture the apartment and the people in it.
Here's the answer. That's the sociocultural perspective. The explanation points to the people around your friend and what's normal in that group, not to the body or to private thoughts.
So the useful question is never "which lens wins?" It's "what does each lens add?"
5. Why common sense isn't enough
You've heard "birds of a feather flock together." You've also heard "opposites attract." Both sound wise, and both feel true. But they predict opposite things about who becomes friends. Common sense has a saying ready for every outcome. That's exactly why it can't tell you which outcome to expect.
Psychology's answer is a principle. Empiricism is the principle that claims should be tested against careful observation and gathered evidence rather than accepted because they feel true or sound sensible. Common sense isn't useless. It's a fine source of ideas. The trouble starts when the feeling of "that's true" is treated as the test.
There's a second trap, and it makes common sense feel stronger than it is. Hindsight bias is the tendency to see an outcome as having been predictable after it is known, the feeling of having known it all along. Think about fans after a basketball game. Once the final score is in, they can explain why the winning team was always going to win. Before the tip-off, some of those same fans may have picked the other side.
Pause and try this. A friend reads that students who take short breaks while studying remember more, and says, "Everyone knew that." What question would show whether this is hindsight bias?
Turn the finding around in your head.
Here's the answer. Ask whether the opposite would also have sounded obvious. "Students who study without breaks remember more" sounds like good advice too. If a finding and its opposite both feel obvious, the feeling isn't evidence, and only gathered data can settle it.
One caveat. Being skeptical of common sense doesn't mean dismissing anyone's experience. Your own sense of what happened to you is real information about you. Empiricism asks only that a claim about people in general gets checked before it's trusted.
6. Theory versus hypothesis
Picture a food-truck owner who notices that sales rise on days the line looks long. She has a broad idea: people trust a place other people already chose. That idea could explain a lot of things, from busy restaurants to popular videos. But it doesn't tell her what to check tomorrow. For that, she needs something narrower.
Here are the two names. A theory is a broad explanation that organizes many observations and is already backed by evidence, and that generates new predictions to test. A hypothesis is a specific prediction, usually drawn from a theory, stated precisely enough that data could show it to be wrong.
That last phrase gets its own word. A claim is falsifiable when it is stated so that some possible observation could show it to be wrong; a claim that fits every possible outcome is not falsifiable.
Here's how they fit together. A theory produces a hypothesis. Data test the hypothesis. If the prediction fails, the theory gets revised or dropped. If it holds, and holds again when others repeat the test, the theory gains support. In everyday talk, people say "I have a theory" when they mean a hunch. In science it's the other way around: the theory is the well-supported explanation, and the hypothesis is the specific, testable guess.
Pause and try this. Someone says, "Customers always do whatever feels right to them." Is that a useful hypothesis?
Ask yourself what result could ever prove it wrong.
Here's the answer. No, because it isn't falsifiable. Any choice a customer makes can be described as what felt right, so no observation could contradict it, and a claim no result can contradict isn't science yet.
Keep this line: the theory explains, the hypothesis predicts, and the data decide.
Closing
Let me pull it together in the order we built it. Psychology studies behavior, which you can see, and mental processes, which you infer from behavior. Wundt's laboratory in 1879 turned a mental process into a number, and the reaction-time sample showed you how a mean, a median, and a range summarize those numbers. The history moved from structuralism and functionalism through psychoanalysis, behaviorism, and the humanistic movement to the cognitive and biological eras. The six perspectives explain one behavior at different levels, and the biopsychosocial model holds them together. Empiricism asks for evidence, because hindsight bias makes any finding feel obvious after the fact. And a theory explains, while a falsifiable hypothesis predicts.
Next in this module come the slide deck, the Readings and Resources page, the lecture tutorial, the practice set, and the quiz. Then, in Week 2, Research Methods and Ethics, we'll take the hypothesis you met in this lecture and learn the designs psychologists use to test it.
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