Functional Magnetic Resonance Imaging

Deception Experiments

Contrasting an experimental condition with a control condition is the principle by which cognitive neuroscientists try to understand which parts of the brain are active while performing a certain task. Researchers will try to design an experiment which comprises two tasks that are identical in every way except for one very specific variable of interest. When the patterns of brain activity are later overlaid and compared for each of the two conditions, any differences in activity are thought to be attributable to the difference in the variable of interest.

In the case of deception experiments, the standard comparison will be to overlay brain activation patterns seen when performing truthful trials of a task (considered to be a baseline, or control) with deceptive trials. The difference observed between the two can then be attributed to deception. The strength of this evidence depends heavily on the sound design of the experimental procedure.

It is important to be aware of the restrictions that fMRI-based research imposes on experimenters and the tasks that they employ with regard to deception. For a participant taking part in an fMRI study, inside the bore of the scanner can be a dark, cold, and noisy environment. Distortions caused by body motion inside the scanner are common, and a great deal of time is spent making participants feel comfortable inside the scanner and training them to remain still throughout the experiment. Participants will usually be asked to make push-button responses on button boxes at their sides rather than speak, as the movement of the tongue and jaw (as well as air over the vocal chords) will introduce distortions into the scanning data because it upsets the carefully controlled magnetic fields within the scanner.

The types of experiments employed in fMRI studies vary greatly in terms of the scenarios in which the experiments are set. Some might employ a mock-crime scenario, in which one must plead innocence either truthfully or deceptively about a staged crime that was enacted prior to the scanning session; others might ask participants questions as to the nature of potentially embarrassing autobiographical information; and some experiments employ emotionally neutral information concealment scenarios, such as lying about a playing card in a hand of cards. Clearly these experimental scenarios will vary in their stakes—the risks or rewards associated with successful deception—as well as the extent to which they induce feelings such as fear of being found out or guilt.

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