involved with the left hand in a different manner from those involved with the right. This is exactly what they found.
Figure 3.6 How Playing Music Affects the Brain
Source: Elbert et al. (1995).
To measure neuronal activity in the brain, these researchers used a brain imaging device, the MEG. They found that neuronal activity in the brain was different between the areas of the brain related to the left and right fingers of musicians. Further, they found that the brain areas of the musicians’ right hands were not different from those of the control group who did not play a musical instrument. Thus, the experimental comparison was between individuals who had played a musical instrument since childhood and the control group, those who had not. There was also a comparison between the brain areas involved with the left and right fingers of the musicians. Further, these researchers examined the correlation between neuronal activity and the length of time an individual had played an instrument. Figure 3.6 shows this relationship. As you can see, this is a negative correlation in that the earlier (lower number) one began to play an instrument, the stronger the neuronal activity was. The experimental and correlational aspects of this research helped the researchers logically conclude that previous experience can influence brain organization. The major point here is that prior experience can influence the brain, which will be an important consideration in fully understanding the development of mental illness and its treatment. For example, therapy for depression changes the flexibility of the brain connections, whereas stress restricts flexibility (Castrén & Hen, 2013).
Logic and Inference: The Detective Work of Science
Perhaps you have heard the story of our friend from Boston who got up every morning, went outside his house, walked around in a circle three times, and yelled at the top of his voice. His neighbor, being somewhat curious after days of this ritual, asked him for the purpose behind his strange behavior. The man answered that the purpose was to keep away tigers. “But,” the neighbor replied, “there are no tigers within thousands of miles of here.” To this, our friend responded, “Works quite well, doesn’t it?”
How could we demonstrate to our friend that his yelling is not causally related to the absence of tigers? One strategy might be to point out that the absence of tigers might have come about for other reasons, including the fact that there are no tigers roaming in the greater Boston area. Our friend’s reasoning was incorrect because it overlooked many other plausible explanations for the obvious absence of tigers. Although our friend sought to infer a relationship between his yelling and the absence of tigers, his inference was weak.
Logic is particularly important in science as an aid to answering this question: What question should my experimental study answer to test my ideas about the world? That is, logic can help us to answer questions of inference. Inference is the process by which we look at the evidence available to us and then use our powers of reasoning to reach a conclusion. Like Sherlock Holmes engaged in solving a mystery, we attempt to solve a problem based on the available evidence. Did the butler do it? No, the butler could not have done it because there was blond hair on the knife and the butler had black hair. But perhaps the butler left the blond hair there to fool us. Like a detective, scientists try to determine other factors that may be responsible for the outcome of their experiments or to piece together available information and draw general conclusions about the world. Also like the detective, the scientist is constantly asking, “Given these clues, what inference can I make, and is the inference valid?” Logic is one method for answering these questions.
Inference: the process by which we look at the evidence available and then use logic to reach a conclusion
What type of evidence would you need to show that a vaccine did not lead to the development of autism?
© iStockphoto.com/Gajus
One example of using logic to help solve a question in psychopathology involved the relationship between giving a child the MMR (measles, mumps, and rubella) vaccine and the development of autism. In the late 1990s, based on one published study (which was later discredited by the journal in which it appeared), it was suggested in the media that the MMR vaccine led to the development of autism. The MMR vaccine is given to a child around 12 to 15 months of age. The first signs of autism appear around 15 to 18 months of age. Thus, it was argued that the vaccine led to the development of autism. What type of evidence would you need to show this was not the case? You might first ask if everyone who receives the vaccine develops autism. Since many who receive the vaccine do not develop autism, then if the relationship exists, it is not a simple one. More important from a logical standpoint, you might ask if there exists a child who did not receive the vaccine but did develop autism. This would help to rule out vaccination being the single cause of autism. As you will see in Chapter 5, a critical finding is that there are signs of autism in children before the age of vaccinations. Thus, logically, researchers were able to rule out vaccines as the single cause of autism.
Validity
Logical procedures are also important for helping us understand the accuracy or validity of our ideas and research. Valid means true and capable of being supported. In studying mental illness, one important way to show that our ideas can be supported is to replicate them with different individuals in different locations. If we hypothesized that a certain type of stress led to depression, for example, then we would need to show that this is the case not only in our research clinic, but also in other clinics.
Historically, we have discussed various types of validity in psychology, which arise from differing contexts. These contexts range from developing types of tests to running experiments. The overall question is this: Does a certain procedure, whether it is a test of mental illness or an experiment, do what it was intended to do? There are two general types of validity (Campbell & Stanley, 1963).
internal validity: the ability to make valid inferences between the independent variables (IVs) and dependent variables (DVs)
external validity: also known as generalizability, the ability to apply the results from an internally valid experiment to other situations and other research participants
generalizability: also known as external validity, the ability to apply the results from an internally valid experiment to other situations and other research participants
The first is internal validity. The word internal refers to the experiment itself. Internal validity asks the following question: Is there another reason that might explain the outcome of our experimental procedures? Students are particularly sensitive to questions of internal validity, for example, when it is time for final exams; they can make a number of alternative suggestions about what the exam actually measures and why it does not measure their knowledge of a particular subject. Like students, scientists look for reasons (threats to internal validity) that a particular piece of research may not measure what it claims to measure. In the case of our friend from Boston, the absence of tigers near his house could have reflected a long-standing absence of tigers in his part of the world rather than the effectiveness of his yelling.
The second type of validity is external validity. The word external refers to the world outside the setting in which the experiment was performed. External validity often is called generalizability. Remember the story of Semmelweis. His finding that the deaths of the mothers who had just given
