important differences between mock-crime laboratory studies and field applications of the polygraph that the external validity of this body of research is as much in doubt as the external validity of other laboratory studies of polygraph test accuracy.

Second, the bulk of the published research lending empirical support to the claim that countermeasures substantially affect the validity and utility of the polygraph is the product of the work of Honts and his colleagues. It is therefore important to obtain further, independent confirmation of these findings from multiple laboratories, using a range of research methods to determine the extent to which the results are generalizable or limited to the particular methods and measures commonly used in one laboratory.

There are also important omissions in the research on countermeasures. One, as noted above, is that none of the studies we reviewed adequately investigated the processes by which countermeasures might affect the deception of deception. Countermeasures are invariably based on assumptions about the physiological effects of particular mental or physical activities and their implications for the outcomes of polygraph tests. The first step in evaluating countermeasures should be a determination of whether they have their intended effects on the responses measured by the polygraph, followed by a determination of whether these specific changes in physiological responses affect the outcomes of a polygraph test. Countermeasure studies usually omit the step of determining whether countermeasures have their intended physiological effects, making any relationships between countermeasures and polygraph test outcomes difficult to evaluate.

Another omission is the apparent absence of attempts to identify the physiological signatures associated with different countermeasures. It is very likely that specific countermeasures (e.g., inducing pain, thinking exciting thoughts) produce specific patterns of physiological responses (not necessarily limited to those measured by the polygraph) that could be reliably distinguished from each other and from patterns indicating deceptive responses. Polygraph practitioners claim that they can detect countermeasures; this claim would be much more credible if there were known physiological indicators of countermeasure use.

A third omission, and perhaps the most important, is the apparent absence of research on the use of countermeasures by individuals who are highly motivated and extensively trained in using countermeasures. It is possible that classified research on this topic exists, but the research we reviewed does not provide an answer to the question that might be of most concern to the agencies that rely on the polygraph—i.e., whether agents or others who are motivated and trained can “beat” the polygraph.

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