Yet Lee acknowledges that jurors are ill-equipped to perform this most basic function. Expert Testimony About Lying Moreover, once we start asking whether jurors can do their job, we may discover that expert testimony is needed to correct other misimpressions as well. In both civil and criminal trials, appeals courts strongly defer to a jury's decision to believe one witness rather than another. This practice is based on the assumption that jurors who see and listen to the witnesses firsthand are in a better position to assess their credibility than a reviewing judge looking at a cold transcript. Yet here too, as with eyewitness testimony, the empirical evidence suggests otherwise.
Studies show that jurors tend to equate signs of nervousness with untruthfulness.
Many practiced liars, however, are cool as a cucumber, while first-time witnesses are often nervous about testifying, quite apart from whether they are telling the truth or not. Moreover, there are cultural biases. The logic of the Lee decision suggests that litigants should be permitted to offer expert testimony about the signs of honesty and dissembling. Indeed, carried to its conclusion, this logic may suggest that a litigant should even be permitted to call an expert to testify that a particular witness exhibited signs of lying visible to the expert. In fact, this was permitted in a celebrated case, the perjury prosecution of accused communist agent Alger Hiss in 1949-50.