International Society for Traumatic Stress Studies

Preliminary Thoughts on a Theory-Driven Model for the A Criterion for PTSD

Posted 1 January 2003 in StressPoints by Dean Lauterbach and Andrew Gloster, Ypsilanti, Michigan

Portions of this paper were presented at the ISTSS 18th Annual Conference. For additional information, contact Dean Lauterbach at or 734/487-0785.

Considerable controversy has surrounded the utility of the A criterion for posttraumatic stress disorder (American Psychiatric Association, 2000). Interested readers can refer to O’Brien (1998) for an extended discussion of the issues. The A criterion is composed of two elements. The first element (A1) states that the “person experienced, witnessed or was confronted with an event or events that involved actual or threatened death or injury or a threat to the physical integrity of self or others” (pp. 463 DSM-IV-TR). The A1 criterion is designed to reflect objective dimensions of the event and, as such, serves a gatekeeper function distinguishing between trauma and stress. Questions remain as to which events can pass through that gate and how such decisions are made.

The second element (A2) of the A criterion is designed to reflect subjective psychological reactions in the immediate aftermath of a trauma. The responses include intense fear, helplessness and horror. While it is important to consider individual responses to the trauma in arriving at diagnostic impressions, many have questioned why these three specific reactions have been the focus of attention.

The DSM is designed to be atheoretical. Decisions regarding which types of trauma (e.g., military combat, violent physical assault and terrorist attacks) or responses (i.e., fear, helplessness and horror) warrant consideration for inclusion in the A criterion are based in part on empirical findings. A logical next step is to exploit extant theory in making decisions regarding the inclusion of responses. In a revision of the original Rescorla-Wagner (1972) learning model, Mackintosh (1983) presents a model that includes applications for determining a priori elements for consideration in the A criterion.

The Rescorla-Wagner model describes the relationship between a conditioned stimulus (CS—e.g., stimuli paired with a trauma) and the magnitude of the conditioned response (CR—e.g., symptoms). The model further predicts that if several conditioned stimuli are presented in a compound and paired with an unconditioned stimulus (US—e.g., trauma), changes in any component are related to and limited by several factors. The strength of the CS-US association that develops in response to a trauma is determined by three characteristics of the US—surprise, duration and intensity. These variables determine the height of the learning asymptote that can be supported by the US, and the learning rate parameter. This model has the potential to address both dimensions of the A criterion: objective dimensions of the stressor and subjective responses to the trauma.

According to the model, surprising events produce more learning. In this context, amount of learning is conceptually equivalent to severity of PTSD symptoms. For example, significant negative reactions are expected in response to the events of September 11, an event unexpected by most. Similarly, the unexpected (surprising) death of a loved one would be more likely to produce significant symptoms than the death of a loved one after a long terminal illness. This model also predicts that events of longer duration would produce more severe PTSD symptoms. People who experienced ongoing physical/ sexual abuse would be expected to have more severe symptoms than those experiencing only an isolated episode. Thus, duration could be assessed across discrete episodes. Last, the model predicts that more severe trauma is likely to result in more severe symptoms of PTSD. In animal literature, intensity of the event is easily quantified—e.g., voltage of shock, decibel of noise blast. In trauma literature, severity can be assessed in a variety of ways including the severity of injuries, degree of personal property loss or perceived degree of life threat. Clearly, the three elements described above (surprise, duration and intensity) often are interrelated, causing difficulty in isolating the effect of each element independently. However, animal literature has provided significant support.

It is believed that embracing such a theory-driven approach to etiology and assessment has the potential to significantly advance the area of traumatic stress. It allows for substantial cross-fertilization with contemporary human and animal learning literature, while not sacrificing the important empirical base that has been developed in the clinical, social, cognitive, and community psychological areas. Moreover, it makes the assumptions regarding the specific dimensions of the trauma explicit. Future researchers are encouraged to consider this framework when designing trauma-based research.

American Psychiatric Association (2000). Diagnostic and Statistical Manual of Mental Disorders (fourth edition, text revision ed.). Washington, DC: American Psychiatric Association.

Mackintosh, N.J. (1983). Theoretical Analysis of Classical Conditioning. In N.J. Mackintosh (Ed.), Conditioning and Associative Learning. New York: Claredon Press.

O'Brien, S.L. (1998). What Constitutes a Stressor. In S.L. O'Brien (Ed.), Traumatic Events and Mental Health. New York: Cambridge University Press.

Rescorla, R.A., & Wagner, A.R. (1972). A Theory of Pavlovian Conditioning: Variations in the Effectiveness of Reinforcement and Nonreinforcement. In A.H. Black & W.F. Prokasy (Eds.), Classical Conditioning II: Current Research and Theory. New York: Appleton-Century-Crofts.

Dean Lauterbach and Andrew Gloster are with Eastern Michigan University, Department of Psychology. Contact Lauterbach at