Hypervigilance is an increase in attention to threatening, potentially threatening, or trauma-relevant stimuli and is a widely reported symptom in post traumatic stress disorder (APA, 2000
). This symptom may have numerous manifestations including constant visual scanning for suspicious behavior in pubic places, an alertness for unusual sounds, noting of entrances and exits in enclosed places, constant checking of locks inside the home, or investigation of circumstances that seem out of the ordinary. Hypervigilance is also critical to theoretical characterizations of the disorder in which attentional biases toward threat is thought to be a central organizing feature in post traumatic thought and behavior (Litz and Keane, 1989
; Chemtob, Roitblat, Hamada, Carlson, and Twentyman, 1988
; Ehlers and Clark, 2000
). Such models posit that increased attentional bias to threat might maintain or even initiate other symptoms in the disorder such as intrusive memories, flashbacks, concentration difficulties, and avoidance behaviors.
Understandably, there has been considerable effort dedicated to understanding the nature and extent of attentional biases in PTSD. The majority of this work has been accomplished through behavioral reaction time tasks such as the emotional Stroop and dot probe paradigm (Dagleish, Moradi, Taghavi, Neshat,-Doost, and Yule, 2001
; Harvey, Bryant, and Rapee, 1996
; McNally, Kaspi, Riemann, and Zeitlin, 1990
; Bryant and Harvey, 1995
; Vrana, Roodman, and Beckham, 1995
). As a whole, these paradigms have produced some support for attentional biases in PTSD, although the reliability of the emotional Stroop effect in PTSD has recently been called into question (Kimble, Frueh, and Marks, 2009). Part of the variability in these tasks may be due to the fact that attention is measured using reaction time and is indirectly inferred through facilitation and/or interference effects. Factors such as motor speed, depression, and motivation may all confound the findings.
Other strategies, such as the use of event related potentials (ERPs), have been more productive in studying attentional biases in PTSD (Metzger, Orr, Lasko, and Pitman,1997
; Metzger, et al., 2002
; Attias, Bleich, and Gilat, 1996
; Kimble, Kaloupek, Kaufman, and Deldin, 2000
; Kimble, Ruddy, Deldin, and Kaufman, 2004
). Using ERPs as an index of attention has distinct advantages, including the ability to link specific neurophysiological processes to discrete psychological states and events. In a recent review and metaanalysis of ERP studies in PTSD, Karl, Malta, and Maercker (2006)
concluded that individuals with PTSD showed increased attention to stimuli when those stimuli were potentially threatening or occurred in a threatening context. This body of work is important in that it illustrates automatic responses to threatening stimuli. Still yet, ERPs do not directly measure the behavioral correlates of hypervigilance. While the work may indicate neural differences in response to threatening stimuli, it is not clear how these neural responses translate into hypervigilant behavior.
Eye tracking is a tool that has remained entirely unexplored in PTSD. Eye tracking potentially fills an important niche in the PTSD literature as it can directly assess hypervigilant behavior without the overlay of facilitation, interference, or reaction time. Patterns in eye fixations, fixation durations, and eye movements provide continuous and non invasive behavioral indices of attention to visual stimuli. Eye tracking has been widely used in cognitive psychology for decades to understand processes such as motivation (Isaacowitz, 2006
), visual attention in reading (Rayner, 1998
; Radach, Inhoff, & Heller, 2002
), scene perception (Rayner, Smith, Malcolm, & Henderson, 2009
), and attention to emotional material (Calva and Lang, 2004
It has only been in the last decade in which researchers have used eye tracking to study visual attention in anxiety disorders. Much of this work has been carried out by Karin Mogg and colleagues at the University of Southhampton and Kaye Horley from the University of Wollongong who have been looking at face perception in individuals with social anxiety disorders. In these tasks, participants are typically shown faces that vary in emotional content and differences in visual scanpath are analyzed based on psychiatric status. This body of work suggests that social phobics may have an initial bias for the processing of threat cues (Mogg, Philippot, and Bradley, 2004
), an effect that is modified under stress and over time (Garner, Mogg, and Bradley, 2006
). Horley and colleagues found social phobics to have fewer fixations on the eyes of facial stimuli (Horley, Williams, Gonsalvez, and Gordon, 2003
), an effect that is particularly evident for angry faces (Horley, Williams, Gonsalvez, and Gordon, 2004
A number of studies have also investigated visual orientation and attention in individuals with phobia. In the majority of these tasks, slides that have a range of objects in them (including a picture of a spider) are shown to individuals who vary in spider fear (Gerdes, Alpers, and Pauli, 2008
; Rinck and Becker, 2006
; Pflugshaupt et al., 2005
; Lange, Tierney, Reinharnd-Rutland, & Vivekananda-Schmidt, 2004
). The data has suggested that spider phobics initially fixate faster on spider stimuli and then avoid them (Pflugshaupt et al., 2005
; Rinck and Becker. 2006
). Other work has shown that spider phobics may be distracted by spider pictures even when the spider pictures are irrelevant to the task (Gerdes, Alpers, and Pauli, 2008
Whether similar patterns of attention exist in individuals with PTSD is still an unanswered question. Individuals with PTSD may, for example, show evidence of initial hypervigilance only to be followed by avoidance of traumatic stimuli. This would be consistent with theories in the wider anxiety literature that indicate that both hypervigilant and avoidant behavior may co occur but are separated temporally—the hypervigilance is present to detect threat so that it can be subsequently avoided (Mogg, Mathews, and Weinman, 1987
: Mogg et al., 1997
; Bradley, Mogg, White, Groom, and de Bono, 1999
). Given that PTSD is characterized by both hypervigilant and avoidant behaviors, a test of this hypervigilance-avoidance hypothesis is in order.
There has only been one study using eye tracking that has looked at visual attention in trauma survivors and it looked only at initial visual orientation. Bryant, Harvey, Gordon, and Barry (1995)
presented four words in the parafoveal range of which one of the words was a threat word. Those motor vehicle accident survivors with PTSD demonstrated more initial eye movements towards the threat words than to neutral words as compared to motor vehicle accidents survivors without PTSD. The authors conclude that PTSD participants preferentially fixate on threat stimuli than do non PTSD participants, particularly in the early stages of processing.
This study intends to expand our understanding of visual attention and vigilance in a traumatized sample. First, we investigated initial visual orienting to negatively valenced, neutral, and trauma-relevant stimuli. Preferential orientation to traumatic stimuli would be a relatively direct measure of hypervigilance and would have high ecological validity. Individuals with PTSD, and veterans in particular, often describe visual scanning after trauma in order to identify potential threats. When given a choice, do veterans with PTSD look first at trauma specific stimuli? We also investigated whether preferential orienting was specific to trauma-relevant stimuli or might include other negatively valenced stimuli. This level of control seemed important given that those with PTSD often describe being hypervigilance for a wide range of threats that exceed the content of their original trauma. Given this pattern, we hypothesized that veterans higher in PTSD symptoms would orient first to negatively valenced stimuli, regardless of whether they were combat or motor vehicle accidents.
Second, we used a paradigm designed to assess visual attention across time to assess patterns of vigilance/avoidance. Despite 25 years as an official diagnosis, the field still has very little understanding as to whether those with PTSD are avoidant of or vigilant for traumatic reminders and threat. Those who highlight avoidance/numbing responses to traumatic reminder emphasize cognitive and behavioral strategies designed to evade stimuli that might remind one of a trauma (Horowitz, Wilner, and Alverez, 1979
). In a forced task paradigm such as this one, one might expect that those with PTSD might preferentially look away from traumatic reminders in order to minimize the onset of intrusive symptoms. On the other hand, an emphasis on the vigilant aspects of the disorder would suggest that those with PTSD would find the traumatic stimuli quicker and then continue to scan the stimulus for potential threat. In addition, theories that emphasize an inability to disengage from traumatic reminders would also suggest vigilance rather avoidance in a PTSD sample (Ellenbogen and Schwartzmen, 2008
; Pineles, Shipherd, Welch, and Yovel, 2006) Finally, its possible, as some theories of attention in anxiety suggest, that attention may be dynamic--with vigilance dominating early stages of visual processing only to be followed by avoidance (Mogg, Mathews, and Weinman, 1987
: Mogg et al., 1997
; Bradley et al., 1999
. In this study we hypothesized that veterans higher in PTSD symptoms would dwell longer the first time they saw a negatively valenced picture, but then subsequently avoid it.
Third, we assessed pupil dilation to negatively valenced and neutral pictures to assess arousal and interest (Sturgeon, Cooper, and Howell, 1989
). The study controlled for general arousal effects by having arousing, but non trauma relevant stimuli (motor vehicle accidents) in addition to neutral stimuli. The literature provides clearer guidance with respect to how individuals higher in PTSD would react to trauma-relevant pictures. Given that individuals with PTSD are known clinically and experimentally to show autonomic sympathetic activation to traumatic reminders, one would expect that those veterans with PTSD would have larger pupils to traumatic stimuli. Whether they would also show larger pupils to non-traumatic, negatively valenced stimuli (motor vehicle accidents) is an empirical question that would shed light on the specificity of post traumatic arousal.