Research from Cardiff and Swansea Universities reveals a tell-tale sign of psychopathy: a lack of pupil dilation when viewing disturbing images. Psychopathic offenders' pupils remained unchanged when shown horrific pictures, unlike non-psychopathic individuals whose pupils dilated. This "psychopathic stare" indicates an insensitivity to threatening stimuli, not a general emotional deficit. The study used non-invasive methods to provide objective physiological evidence of this emotional deficit, potentially aiding future clinical assessments and interventions.

Prepared by Olivia Bennett and reviewed by editorial team.