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Essays
Control groups
In Chapter 2, we talk several times about this or that brain area being activated during some particular activity-so that certain areas in the occipital lobe are especially activate when someone is examining a visual stimulus, certain areas of the frontal lobe are especially activate when someone is listening to a verbal input, and so on. We need to be clear, though, about what these claims really mean.
All cells in the brain are active all the time. When receiving some input, however, or when working on a particular process, the brain cells change their activation level. Therefore, when we talk about, say, the occipital lobe's response to a visual input, we do not mean that the cells are active when an input arrives and inactive the rest of the time. Instead, we're saying that, when a visual input arrives, the activity in the occipital lobe increases from its prior (baseline) level.
To measure these increases, though, we need a basis for comparison, and, indeed, this is a consistent feature of scientific investigation: We often can interpret a fact, or a measurement, or an observation, only with reference to some appropriate baseline. This is true outside of science as well: Imagine that your school's football team wins 90% of its games when you're wearing your lucky socks. Does this mean the socks are helpful? We'd need to ask how often the team wins when you're not wearing your socks; if that number is also 90%, then your socks have no effect at all.
In scientific research, our basis for comparison, in evaluating our data, is usually provided by a control condition-a setup that allows us to see how things unfold in the absence of the experimental manipulation. If, therefore, we want to understand how the brain responds to visual inputs, we need to compare a condition with a visual input (the experimental condition) with a control condition without this input.
But how should we set up the control condition? Imagine, as one possibility, that participants in our experimental condition are staring attentively at a computer screen, eagerly awaiting (and, eventually, seeing) a visual stimulus, while the participants in our control condition are told merely to hang out, so that we can observe the functioning of their brains. If we found differences between these two conditions, we could draw no conclusions. That's because any differences we observe might be due to the presence of the visual stimulus in one condition, or they might be due to the fact that participants in one condition are attentive while those in the other condition are relaxed. With no way to choose between these options, we'd have no way to interpret the data.
Clearly, then, our control condition must be carefully designed, so that it differs from the experimental condition only in the presence or absence of the crucial variable (in our example, the visual stimulus). With this, we want to make sure that participants in the two conditions get similar instructions, and have similar expectations for the experiment. Only then will the contrast between the conditions be meaningful, allowing us to interpret the data and thus to test our hypothesis.
Detecting Lies
It is obvious that people sometimes lie to the police, and, of course, the police do all they can to detect this deception. Some police officers claim that they can tell, during an interview, whether a suspect is lying to them or not, but, in truth, most people (and most police!) are not skilled in making this determination. This is one of the reasons why law enforcement often relies on a machine called the polygraph, or, as it's more commonly known, the "lie detector." This device is designed simply to measure moment-by-moment changes in someone's breathing, heart rate, blood pressure, or amount of perspiration. To use these measurements for lie detection, we rely on the fact that someone who is lying is likely to become anxious about the lie, or tense. These emotional changes, even if carefully hidden by the test subject, are associated with changes in the biological markers measured by the polygraph, and so, by using the polygraph to detect these changes, we detect the lie.
Unfortunately, though, this procedure is of questionable value. The polygraph often fails to detect lies, and, just as bad, the test often indicates that people are lying when they are not. In addition, it is possible to "beat the test" by using certain strategies. One strategy is for the test subject to engage in fast-paced mental arithmetic throughout the test. This produces its own increase in heart rate, perspiration, and so on, and so masks any changes that might be produced by lying!
A different lie-detection technique is less commonly used, but more promising. The Guilty Knowledge Test (or GKT) doesn't rely on measurements of emotion in order to detect the lie. Instead, the test seeks to detect the cognition associated with lying. Specifically, the test relies on the fact that, in many crimes, there will be certain facts that no one knows other than the police and the guilty party. This allows the police to ask questions like, "Was the injured woman's scarf: (a) red? (b) green? (c) blue? (d) white?" A criminal might refuse to answer, claiming to have no knowledge, but, even so, the criminal will almost certainly show an orienting response when the correct answer is mentioned. It is as if the criminal cannot help 'perking up' in response to the one option that's familiar, and cannot help thinking, "Yes, that was it," even though he overtly insists that he does not know the answer!
The orienting response involves changes in the electrical activity of the brain, and these changes can be detected by suitable measurements on the surface of the scalp. In this way, the orienting response can be objectively recorded even if the criminal makes no overt response, and denies any knowledge of the crime.
The orienting response itself is relatively easy to detect, making the test procedure reasonably accurate. However, the GKT has its own limits. The test can be run only if the police can identify an adequate number of test items (facts that the perpetrator would certain know, but that no one else would). Even with these limits, though, the GKT is being adopted by some law enforcement agencies. It appears, then, that our understanding of the brain, and how people react to meaningful stimuli, can provide an important new tool for the detection of guilty knowledge, and thus the detection of lies.
To learn more about this topic in cognitive psychology and the law:
Ben-Shakhar, G., Bar-Hillel, M., & Kremnitzer, M. (2002). Trial by polygraph: Reconsidering the use of the Guilty Knowledge Technique in court. Law and Human Behavior, 26, 527-541.
Honts, C. et al., (1994). Mental and physical countermeasures reduce the accuracy of polygraph tests. Journal of Applied Psychology, 79, 252-259.
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