HYPERVIGILANCE in the real world: An eye tracking study.

Roxanne BrownleeSupervisor: Dr. Lili TCheang

What is Hypervigilance?• Hypervigilance is a signature symptom of Posttraumatic

Stress Disorder (PTSD): an anxiety disorder which develops following the experience of extreme trauma.

• Individuals experiencing PTSD report feeling constantly on guard. It is a mentally and physically draining state of being, which is believed to prompt the flashbacks, dreams and negative image intrusions which also characterise PTSD.

• It is believed that the hypervigilant state is self-perpetuating; individuals are constantly in threat-detection mode, and react out of proportion to the threats encountered. When threat is encountered, the over-reactive fear circuit is reinforced (Buckley, Blanchard & Neill, 2000).

However……

Hypervigilance is poorly understood.

Why do we care?Anxiety disorders tend to overlap in symptoms. This makes it difficult to make conclusive diagnoses based on patient reports and clinician assessments.

Hypervigilance appears to distinguish PTSD from other anxiety disorders, and possesses impressive diagnostic sensitivity over the remaining symptoms of the disorder (Halowka, Marx, Koupek & Keane 2012).

Hypervigilance may be integral to the maintenance and prognosis of PTSD. A clearer understanding of the processes involved could help improve diagnostic tools and intervention/treatment designs.

Measuring Hypervigilance• Hypervigilance is frequently linked to

the cognitive phenomenon of attention bias towards threat. This means paying closer attention to threatening information in the environment, and/or doing so for longer.

• Attention bias in the cognitive literature is typically assessed using the Emotional Stroop Task or the Dot Probe Task. However, there are many reasons why these are inappropriate paradigms for investigating hypervigilance.

The Emotional Stroop Task

FLOWER BLOOD

• Participants are asked to respond as rapidly as possible to the COLOUR of the word, and ignore the semantic meaning.

• PTSD typically respond more slowly to threat-related words.

• This “interference” is taken to signify an attentional bias towards threat, suggesting that the participant’s relation to the emotional content of the word led to delayed responding.

HOWEVER…• Response times are an INDIRECT measure of attention.• In PTSD patients, this paradigm has produced very INCONSISTENT findings

and may be an inappropriate means of assessment (Kimble et al., 2009).

The Dot Probe Paradigm• Participants respond to the location of a

probe after two stimuli are presented, one threatening and one neutral.

• Participants respond to the location of the probe faster when it is placed in the location they were already attending to.

• In anxious individuals, attention typically has previously rested on the threatening stimulus, and thus response to the probe is FACILITATED if it has been placed in the same location.

BUT• Real world stimuli cannot be dichotymised into either threatening or neutral.

• Stimuli in the real world are not presented in flashes.

• Still indirect, as facilitated responding is taken to IMPLY attention.

Eye-Tracking Hypervigilance• Eye-tracking is believed to be an

uncontroversial measure of attention.• Eye tracking allows for a direct

measure of attentional bias as it does not infer from response times, or require motor/verbal responses from participants.

• Eye-tracking is a novel approach in the study of hypervigilance, and the studies that have used eye-tracking have only done so in laboratory settings.

• Participants do not report feeling hypervigilant in controlled laboratory settings.

• CAN WE REALLY GENERALISE?

• Hypervigilance is at its peak when PTSD suffers are out and about in public places.

HOWEVER…

Naturalistic Eye Tracking• Eye-tracking has already been used to demonstrate the

synchrony between eye-movements and attentional processes in every day tasks, such as walking.

• Gaze tends to depend on the stimuli in the environment that are behaviourally relevant.

• Might naturalistic eye tracking be able to provide insight hypervigilance in PTSD suffers, using analysis of gaze allocation tendencies while moving around in a vulnerable, public space?

The Current Study• Uses naturalistic eye-tracking in a real world street walking task to

explore differences in stimulus preferences across hypervigilant PTSD ex-servicemen, non-PTSD ex-servicemen and age matched controls.

---WHAT are they looking at?---

• A novel and ecologically valid approach to measuring hyperviligance which combats many of the limitations of the cognitive paradigms described earlier.

• The research is largely exploratory in nature, but it is hypothesised that there will be significant differences in the sorts of stimuli the different groups appear to preferentially allocate their gaze towards.

METHODSParticipants

Ex-servicemen PTSD

Mean Age: 42.65

Ex-servicemen non-PTSD

Mean Age: 39.5

Healthy controls

Mean Age: X

12 16 14

• Participants walked a set route wearing a head-mounted, portable eye tracking device which simultaneously recorded images of the pupil’s movements as well as the observing environment.

• A purpose-built MATLAB program was used to track movement of the pupil across the scene.

• Video files were coded frame by frame for the 3600 frame defined portion of the walk. Objects participants looked at were coded according to an agreed list of labels of the stimuli that were available for viewing throughout the session.

• A second coder assisted with the process to reduce experimenter bias.

• A series of One-Way ANOVAS were performed to determine differences between stimuli preferences across groups.

*

* The video data for both the ex-servicemen PTSD and non-PTSD group had been collected by Stewart (2012) in a previous study. In the current study, only the data from the control group was actively collected. The apparatus, routes, and assisting MATLAB program were all the same.

Results

LimitationsIt is possible to visually fixate on one location while simultaneously diverting attention to another. Results must be interpreted with caution.

While the route in the current study was selected for its relatively stable environment, certain variables could not be controlled for, such as the occasional moving pedestrian or vehicle. Might have led to inconsistent gaze allocation across participants.

Varying lighting conditions meant that location of the public was sometimes undetectable. This resulted in a variable number of frames “missing” for each participant. This may have dramatised differences between participant groups.

Future Directions

Might consider combining with the measurement of electrophysiological activity.

Important to make comparisons with PTSD sufferers from different trauma classes such as rape/assault.

Important to compare with other anxiety disorders to ensure effect is unique.

Potential to develop eye-tracking as a diagnostic tool for PTSD.

References