9 All of this epidemiological work has been substantially supported by the more empirical work. Laboratory studies have shown PTSD sufferers to have marked and significant response to noxious stimuli, with sufferers showing both psychological distress and physiological reactivity to battle sounds, war imagery and the like, and marked avoidance of these stimuli: 80% of PTSD sufferers in one study terminated exposure to audiotaped combat stimuli as opposed to 0% healthy combat veterans (39). Studies of sleep show traumatic dreams occurring in both REM and non-Rem sleep, as well as difficulties in both falling asleep and maintaining sleep. In general, the sleep studies show a wide range of differences between PTSD sufferers and other populations, both civilian and military. Other studies, investigating intrusive cognitive activity, have shown marked effects of intrusive cognitions, with PTSD sufferers showing positive interference for Vietnam-related words (BODYBAG), but not for other intrusive words (GERMS) (40). Thus, some of the key features of PTSD, sleep disturbance, intrusive cognitions, psychological reactivity and physiological distress, seem to be supported empirically, and there is support for the notion of a specific disorder produced by trauma, and capable of being delineated from other disorders. Thus, it seems clear that exposure to violence has severe, persistent and delayed sequelae, with a possible dose-response effect, but there still remain some difficulties, and some critics of the idea of PTSD being the unifying concept fro post traumatic disorders. The major critics come from amongst those working with torture survivors, who are critical of many aspects of the PTSD definition (41-42), whilst others suggest that there may still be such a thing as a "torture syndrome" apart from PTSD (43). Reeler (1993) has argued in favour of a torture syndrome, whilst also arguing against a narrow medical definition of the effects of trauma such as torture (43). There are also other critics who argue against a narrow medical definition for the effects of torture (44), and this debate will continue for some time.