Abstract
Detecting whether a suspect possesses incriminating (e.g., crime-related) information can provide valuable decision aids in court. To this means, the Concealed Information Test (CIT) has been developed and is currently applied on a regular basis in Japan. But whereas research has revealed a high validity of the CIT in student and normal populations, research investigating its validity in forensic samples in scarce. This applies even more to the reaction time-based CIT (RT-CIT), where no such research is available so far. The current study tested the application of the RT-CIT for an imaginary mock crime scenario both in a sample of prisoners (n = 27) and a matched control group (n = 25). Results revealed a high validity of the RT-CIT for discriminating between crime-related and crime-unrelated information, visible in medium to very high effect sizes for error rates and reaction times. Interestingly, in accordance with theories that criminal offenders may have worse response inhibition capacities and that response inhibition plays a crucial role in the RT-CIT, CIT-effects in the error rates were even elevated in the prisoners compared to the control group. No support for this hypothesis could, however, be found in reaction time CIT-effects. Also, performance in a standard Stroop task, that was conducted to measure executive functioning, did not differ between both groups and no correlation was found between Stroop task performance and performance in the RT-CIT. Despite frequently raised concerns that the RT-CIT may not be applicable in non-student and forensic populations, our results thereby do suggest that such a use may be possible and that effects seem to be quite large. Future research should build up on these findings by increasing the realism of the crime and interrogation situation and by further investigating the replicability and the theoretical substantiation of increased effects in non-student and forensic samples.
Highlights
Valid lie detection tests would provide valuable means in police interrogations and court, yet most lie detection test that have been developed so far are not endorsed by the scientific community
The 2 × 2 ANOVA on the error rate revealed a significant main effect of Group, F(1, 50) = 6.06, p = 0.017, np2 = 0.11, with a higher error rate for the inmates compared to the control group
It revealed a significant main effect of Item, F(1, 50) = 24.43, p < 0.001, np2 = 0.33, with a higher error rate for critical compared to neutral items. These effects were qualified by a significant interaction of Group x Item, F(1, 50) = 5.90, p = 0.019, np2 = 0.11, with a larger Concealed Information Test (CIT)-effect in the inmates t(26) = 4.30, p < 0.001, d = 0.83, compared to the control group, t(24) = 2.66, p = 0.014, d = 0.53
Summary
Valid lie detection tests would provide valuable means in police interrogations and court, yet most lie detection test that have been developed so far are not endorsed by the scientific community. It has been found that such recognition leads to measurable changes in different autonomic indices, as for instance an increase in skin conductance, and a decrease in heart rate and respiration for the critical crime knowledge compared to the other neutral answer alternatives [7]. No such changes should be observable in an unknowledgeable suspect, for which all alternatives should be likely.
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