compare individuals to each other. Concepts such as feeble mindedness cannot be defined using a single intelligence test, as there are many factors that the test does not examine, such as volitional and emotional variables. Tone Variator Stern invented the tone variator in 1897, which allowed him to study human sensitivity to changes in sound. Whereas his predecessors had limited themselves to studying thresholds and noticeable differences using constant, discrete stimuli, Stern studied the continuous change of one stimulus into the next. Forensic Psychology Stern was a pioneer in the field that would become forensic psychology. Like Hugo Münsterberg, Stern explored the psychology of eyewitness testimony with particular attention to its accuracy. A student of memory research pioneer, Hermann Ebbinghaus, Stern had participants look at photographs and later asked them to recall details. He collaborated with criminologist, Franz v. Liszt, and in 1901 conducted a study in which law students witnessed a staged classroom argument in which one protagonist drew a revolver at which point the professor stopped the mock fight. Students were then asked to give written and oral reports of the event. Stern and Franz found that, in such demonstrations, the subsequent recall was poor when tension was high, leading them to conclude that emotional states could affect eyewitness testimony. Other studies investigated the impact of questioning techniques, differences between children and adult witnesses, differences between male and female witnesses, and the way events occurring between the time of an event and the time of recall can affect the accuracy of testimony. Stern noted that memory was fallible and sought ways to differentiate between intentional and unintentional falsification of testimony. These findings had the potential to improve the criminal justice system and illustrated practical applications of psychological research. Stern also noted the effects that the courtroom could have on children and advocated for the consultation of a professional psychologist whenever child testimony was used. Stern also hypothesized that men were more reliable witnesses than women but subsequent work has challenged this suggestion. The study found there to be no significant sex differences among the participants concerning recall accuracy and resistance to false information. Stern's early work in forensic psychology has allowed for follow-up and scrutiny. Publications Stern, W. (1900). Über Psychologie der individuellen Differenzen: Ideen zu einer 'differentiellen Psychologie’ (On the psychology of individual differences: Toward a ‘differential psychology’). Leipzig: Barth. Stern, W. (1906). Person und Sache: System