Quantifying Human Avoidance Behavior in Immersive Virtual Reality

Abstract

Avoidance behavior is a key symptom of most anxiety disorders and a central readout in animal research. However, the quantification of real-life avoidance behavior in humans is typically restricted to clinical populations, who show actual avoidance of phobic objects. In experimental approaches for healthy participants, many avoidance tasks utilize button responses or a joystick navigation on the screen as indicators of avoidance behavior. To allow the ecologically valid assessment of avoidance behavior in healthy participants, we developed a new automated immersive Virtual Reality paradigm, where participants could freely navigate in virtual 3-dimensional, 360-degrees scenes by real naturalistic body movements. A differential fear conditioning procedure was followed by three newly developed behavioral tasks to assess participants' avoidance behavior of the conditioned stimuli: an approach, a forced-choice, and a search task. They varied in instructions, degrees of freedom, and high or low task-related relevance of the stimuli. We initially examined the tasks in a quasi-experiment (N = 55), with four consecutive runs and various experimental adaptations. Here, although we observed avoidance behavior in all three tasks after additional reinforcement, we only detected fear-conditioned avoidance behavior in the behavioral forced-choice and search tasks. These findings were largely replicated in a confirmatory experiment (N = 72) with randomized group allocation, except that fear-conditioned avoidance behavior was only manifest in the behavioral search task. This supports the notion that the behavioral search task is sensitive to detect avoidance behavior after fear conditioning only, whereas the behavioral approach and forced-choice tasks are still able to detect "strong" avoidance behavior after fear conditioning and additional reinforcement.

Facing Your Fear in Immersive Virtual Reality: Avoidance Behavior in Specific Phobia

“…They were informed about the procedure and gave their written informed consent. Next, the electrodes for the one channel eMotion Faros 180 electrocardiography device from BioSign and the 18 sensors of the Perception Neuron V2 motion tracking system were attached to the torso, limbs, and head and then calibrated (see Binder and Spoormaker, 2020 for details). The participants put on the HTC Vive Pro + Eye VR goggles and the HTC in-ear headphones and the automated procedure was started.…”

“…Afterward, the participants were instructed to behave in the VR as in the real world and not to walk through virtual objects, as they could represent real ones. The introduction continued with some tasks to familiarize participants with navigation and item collection as described in Binder and Spoormaker (2020) . At the end of the introduction, the spider and the turtle were sequentially presented in a small side room behind a glass pane (see Figure 1A ).…”

“…The VR was generated in Unity 3D Pro (version: 2020.2.2f1). We used the same setup and scenarios with a field of 4.6 m × 4.3 m, as in Binder and Spoormaker (2020) . Instead of fear conditioned balloons, we used a spider (“Giant Spiders Animated,” version 1.0.0, “spider_hi_004” scaled by 0.03, length: 8 cm, Figure 1C ) as aversive stimulus and a turtle (Chinese box turtle, version 1.0.4, “PondTurtleMiddlePoly” scaled by 0.7, size: length: 14 cm, Figure 1F ) as neutral stimulus, which were purchased in the Unity 3D asset store.…”

“…The electrocardiography signal was analyzed in Matlab using the PhysioNet-Cardiovascular-Signal-Toolbox (version 1.0.2; Vest et al, 2019 ) as described in Binder and Spoormaker (2020) resulting in a timeseries of RR intervals, which represent the duration between successive heartbeats, stored at 250 Hz.…”

“…They showed that spider-fearful participants had an increase in state anxiety, spent more time looking at spiders, and were more engaged in spontaneous avoidance behavior toward spiders. In our previous work ( Binder and Spoormaker, 2020 ), we used the iVR approach to examine if we could objectively quantify avoidance behavior after Pavlovian fear conditioning. In our setup, the healthy participants wore VR goggles and a full-body motion tracking system that provided a virtual representation of participant’s body in the artificial environment.…”