انطباق به عنوان یک نمایش حسی در اضطراب خصلتی: مطالعه با واقعیت مجازی

Twenty-four volunteers were recruited on the basis of their trait anxiety scores (low trait anxiety [LTA] and high trait anxiety [HTA]) as assessed by the State-Trait Anxiety Inventory. Adaptation to conflicting visual–vestibular stimulation (VVS) was used to study integration of space-related multi-sensory information in trait anxiety. First, vestibular perception was assessed by rotating the blindfolded subjects about the vertical axis (horizontal plane rotations) on a remote-controlled mobile robot. The subjects were asked to indicate the perceived rotation by use of an angular pointer. Subjects were then immersed into the center of a visual virtual square room by means of a head-mounted display. They were asked to control the robot with a joystick in order to perform 90° rotations in the virtual room. However, a gain of 0.5 was introduced between visual scene and robot rotation so that the subjects were submitted to a conflict situation in which the 90° rotational visual input was concurrent with a 180° vestibular input. After 45 min of training with the virtual reality display, subjects were tested again in total darkness in order to determine whether their vestibular system had been reset by the conflicting visual signals. We found significant differences in adaptation to VVS between HTA and LTA groups as well as between males and females. Subjects of the HTA group demonstrated larger adaptation than that of the LTA group. Males also showed a greater level of adaptation compared to females. Our results suggest greater visual dependence in HTA subjects. This might be important for understanding the mechanisms underlying pathological anxiety and particularly agoraphobia.

The relationship between emotion and dizziness has been studied for centuries (de Sauvages, 1771; Benedikt, 1870). Schilder (1933) insisted on the importance of the vestibular system for understanding neuroses and psychoses because of its importance in the dynamics of the body image. Indeed, dizziness, which can result from a distorted vestibular input, is an associated symptom of several psychiatric disorders (Brandt, 1996). Dizziness is also a key symptom of panic (Kenardy, Evans, & Oei, 1992). In their study on panic attack symptomatology, Cox and colleagues found that dizziness was experienced by almost all their panic disorder patients (N = 212) (Cox, Swinson, Endler, & Norton, 1994). Thus, many studies have tried to find vestibular dysfunction in panic and agoraphobic patients, but so far a consistent pattern of vestibular dysfunction in panic disorder has not been demonstrated (see Asmundson, Larsen, & Stein, 1998 for a review). Several studies agreed, however, to suggest a possible problem with multisensorial integration in some of these patients: subjects with symptoms of panic and agoraphobia are destabilized under conflicting sensory conditions while maintaining upright posture Yardley, et al. 1995, Yardley, et al. 1994, Jacob et al. 1996 and Jacob et al. 1997. An abnormal vulnerability to destabilization by visual or proprioceptive sway-referencing was demonstrated in these patients using dynamic posturography. 1 Dynamic posturography is the only vestibular test involving a sensory conflict situation. The dizziness symptomatology is thought to be linked to a strategy for maintaining balance or orientation by relying on visual cues, although a recent study attributed a stronger role of proprioceptive cues for maintaining balance in agoraphobic patients (Jacob et al., 1997). The results of all studies employing dynamic posturography emphasize the possible role of central processes of multi-sensorial integration in anxiety disorders. From all these data, it is striking to note that altered visual–vestibular interaction has often been observed in anxious patients, although it is unclear if reported vestibular abnormalities are specific to panic disorder and agoraphobia (Simon, Pollack, Tuby, & Stern, 1998). Three main sensory systems (visual, vestibular, and somatosensory) subserve static and dynamic spatial orientation, and are necessary to control posture and locomotion. Projections of vestibular neurones are found in many brain structures (O'Mara, Rolls, Berthoz, & Kesner, 1994) and in cortex (Grüsser & Güldin, 1995). Semicircular canal and otolith output allows obtaining subjective head orientation via different pathways. Dizziness symptomatology may then be dependent on central processing (i.e., at the level of integration of different sensory modalities related to space perception). Accordingly, a peripheral vestibular abnormality would not be sufficient to explain certain types of anxiety symptoms while relative weighting of different information directly related to space processing needs to be carefully studied. To address this question, we employed a dimensional and symptom-oriented approach, which aims at linking psychiatry to the understanding of normal physiopathological processes. In this context, we chose to work on the basis of trait indices rather than on pathological ones, seeking processes which could be of importance for the development of anxiety disorders (and not only panic disorder). To increase the strength of the design of our study (see Cohen, 1988) we selected two groups of subjects representing extreme scores on the State-Trait Anxiety Inventory (STAI; Spielberger, Gorsuch, Lushene, Vagg, & Jacobs, 1983). As perceptual conflict situations have been exhibited as key features in anxious patients, we studied a situation in which such a conflict would be encountered. In light of what Andreasen (1997) has described as “scientific psychopathology,” we aimed at identifying the normal cognitive process of sensory adaptation in order to understand their possible dysfunction in anxiety disorders. To that end, we employed a new visual–vestibular integration test procedure to characterize the sensory integration in anxiety disorders. The flexibility of spatially coordinated behavior may be studied by temporarily distorting the normal relationship between one stimulus dimension and another, and measuring the adaptive changes that occur in selected perceptual and perceptual-motor tasks. We studied adaptation to sensory conflict during immersion in a virtual environment. During this procedure, vestibular inputs were in conflict with visual information. After a certain time of exposure to such a conflict, we expected that the vestibular system would be re-calibrated according to visual information. Two concurrent hypotheses could be envisaged. According to the literature, we expected that anxious subjects would be more dependent on vision Yardley, et al. 1994, Yardley, et al. 1995, Jacob et al. 1995 and Jacob et al. 1996. However, we did not know how this dependence would manifest itself, since our test did not involve postural control and differed with dynamic posturography. In the latter, subjects have to ignore proprioceptive and/or visual information and rely on vestibular information in order to maintain balance in the most difficult conditions (for example to ignore proprioceptive information when the platform is sway-referenced, and to rely only on visual and vestibular cues). Because patients were unable to rely on vestibular information alone, it is possible that anxious subjects would not use vestibular information in our test. Vestibular perception would thus be typically ignored and remain unchanged. By contrast, anxious subjects also could have an increased vestibular sensibility Jacob, Moeller, Turner, & Wall 1985 and Swinson et al. 1993. Therefore, if they were visually dependent, these subjects could recalibrate their vestibular perception according to visual information.