Background. We examined the effect of a second interviewer's demeanour on cues to deception. We predicted that a supportive demeanour would be the most beneficial for eliciting verbal cues to deceit, as it would encourage truth tellers, but not liars, to say more. In addition, we examined the extent to which interviewees deliberately made eye contact with the interviewers. Liars take their credibility less for granted than truth tellers, and therefore have a greater drive to be convincing. Liars are thus more likely to monitor the interviewer to determine if the interviewer appears to believe them.
Method. Participants appeared before two interviewers: the first asked all the questions and the second remained silent. The second interviewer exhibited either a supportive, neutral, or a suspicious demeanour.
Results. Truth tellers provided significantly more detail than liars, but only in the supportive second interviewer condition. The effect of a second interviewer's demeanour on detail was perhaps remarkable given that the interviewees hardly looked at the second interviewer (less than 10% of the time). Liars displayed more deliberate eye contact (with the first interviewer) than truth tellers did.
Conclusions. A supportive second interviewer has a positive effect on interviewing. We discuss this finding in the wider contexts of investigative interviewing and interviewing to detect deception.