Studies of mental countermeasures have also produced inconsistent findings. Kubis (1962) and Wakamatsu (1987) presented data suggesting that some mental countermeasures reduce the accuracy of polygraph tests. Elaad and Ben-Shakhar (1991) present evidence that certain mental countermeasures have relatively weak effects, findings that are confirmed by Ben-Shakhar and Dolev (1996). Timm (1991) found that the use of posthypnotic suggestion as a countermeasure was ineffective. As with the research reviewed above, studies of the effects of mental countermeasures have failed to develop or test specific hypotheses about why specific countermeasures might work or under which conditions they are most likely to work. There is evidence, however, that their effects operate particularly through the electrodermal channel (Ben-Shakhar and Dolev, 1996; Elaad and Ben-Shakhar, 1991; Kubis, 1962).

A series of studies by Honts and his colleagues suggests that training subjects in physical countermeasures or in a combination of physical and mental countermeasures can substantially decrease the likelihood that deceptive subjects will be detected by the polygraph (Honts, 1986; Honts et al., 1996; Honts, Hodes and Raskin, 1985; Honts, Raskin, and Kircher, 1987, 1994; Raskin and Kircher, 1990). In general, these studies suggest that physical countermeasures are more effective than mental ones and that a combination of physical and mental countermeasures is probably most effective. These studies have involved very short periods of training and suggest that countermeasures are effective in both comparison question and concealed information test formats.

Several important limitations to the research on countermeasures are worth noting. First, all of the studies have involved mock crimes and most use experimenters or research assistants as polygraph examiners. The generalizability of these results to real polygraph examinations— where both the examiner and the examinee are highly motivated to achieve their goals (i.e., to escape detection and to detect deception, respectively), where the examiners are skilled and experienced interrogators, where admissions and confessions are a strong factor in the outcome of the examination, and where there are important consequences attached to the polygraph examination—is doubtful. It is possible that the effects of countermeasures are even larger in real-life polygraph examinations than in laboratory experiments, but it is also possible that those experiments overestimate the effectiveness of the measures. There are so many