Читать книгу Introduction to Abnormal Child and Adolescent Psychology - Robert Weis - Страница 131

Researchers are usually not satisfied with knowing that variables correlate. They also want to determine whether a change in one variable causes a corresponding change in another variable. The best way to establish causality is to conduct an experiment. In an experiment, researchers randomly assign participants to two or more groups. They manipulate one variable (i.e., the independent variable) and hold all other factors constant. Then, they examine the effects of their manipulation on a second variable (i.e., the dependent variable). Experiments allow causal inferences because researchers randomly assign participants to different groups at the onset of the study and treat groups identically throughout the duration of the study. If groups differ at the end of the study, the researchers can conclude that their manipulation of the independent variable caused this difference (Kazdin, 2017).

Random assignment is essential for experimental research. Random assignment implies that each participant has an equal chance of being assigned to each of the groups. By randomly assigning participants, researchers decrease the likelihood that groups differ in meaningful ways before the study. Without random assignment, differences between the groups that emerge at the end of the study might be attributable to differences that existed at its beginning, rather than to the manipulation of the independent variable itself.

A randomized controlled trial is a special type of experiment used to test the efficacy of treatment. Typically, researchers recruit participants with the same disorder from mental health clinics, hospitals, or the community. Then, researchers randomly assign participants to at least two groups: a treatment group that receives the intervention, and a control group that is used for comparison. Participants in the two groups are treated the same, except for the manipulation of the independent variable—in this case, the treatment. At the end of the study, researchers expect to see better outcomes among participants who received treatment than controls.

Let’s look at an example of a randomized controlled trial designed to investigate the efficacy of neurofeedback, a popular and relatively new treatment for ADHD.

Neurofeedback (sometimes called “neurotherapy” or “brain training”) rests on the premise that children with ADHD show atypical brain activity. This atypical brain activity, in turn, leads to problems with attention, concentration, and impulse control. In neurofeedback, children learn to regulate their brain activity to decrease ADHD symptoms (Thibault, Lifshitz, & Raz, 2017).

In a typical neurofeedback session, a clinician uses a device called an electroencephalogram (EEG) to measure the child’s brain activity in real time. Electrodes placed on the child’s scalp measure the wavelength of electrical activity in various brain regions, especially areas responsible for attention and concentration. Two wavelengths are especially important: low-frequency theta waves that reflect a state of inactivity and mental drowsiness and high-frequency beta waves that reflect a state of attention and alertness. Children with ADHD tend to show an abundance of low-frequency theta waves and relatively fewer high-frequency beta waves than children without the disorder. This atypical brain activity is believed to underlie their attention problems (Loo & Makeig, 2013).

Information from the EEG is delivered to a computer that converts it to a visual image on a screen. The child can learn to control the image by altering his or her brain activity. For example, the child might see a dolphin on the computer screen. When the EEG shows low-frequency theta waves, the dolphin stops swimming and floats to the surface. However, when the EEG shows high-frequency beta waves, the dolphin swims faster, dives to the ocean floor, and collects treasure. Children learn to control the dolphin’s actions and earn treasure by regulating their brain activity (Image 3.4).

Image courtesy of Pixabay Creative Commons

Children can learn to decrease theta and increase beta activity over time. Some clinicians believe that as children’s capacity to control their brain activity increases, so too will their attention and concentration. Training can take several months with multiple sessions each week (Janssen et al., 2017).

To evaluate neurofeedback, researchers recruited a sample of children with ADHD and randomly assigned them to either a treatment or control group. Children in the treatment group received neurofeedback, while children in the control group did not. To evaluate outcomes, the researchers asked parents to rate children’s symptoms before and after the study. As expected, the parents of children who received neurofeedback reported significant improvement, whereas the parents of children in the control group did not (Steiner, Frenette, Rene, Brennan, & Perrin, 2014).