According to Marc Whittmann, empirical evidence exists for the association between a person’s level of impulsivity and accuracy of time perception. A study in Germany has correlated fMRI activation of the brain’s core control network, which includes the insular cortex, and two self-reported questionnaires: the Barratt Impulsiveness Scale, BIS; and the Zimbardo Time Perspective Inventory, ZTPI. Results indicated that activation in the brain’s core control network is related to cognitive time management, and that more impulsive individuals tend to under-reproduce time duration more strongly. That is, participants who scored high in impulsivity measures showed some reduced ability to perceive duration of time accurately. Study results suggest that the accumulation of physiological changes in a person’s body states constitutes his/her experience of time. Perception of duration of time, therefore, is subjective and can differ depending on what is going on for a given brain at any given moment. Other studies by Anna Smith of the Institute of Psychiatry in the UK have found that children with ADHD performed poorly on time reproduction tasks, suggesting that these children may have a perceptual deficit related to time discrimination.