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Humans use their eyes not only as visual input devices to perceive the environment, but also as an action tool in order to generate intended effects in their environment. For instance, glances are used to direct someone else's attention to a place of interest, indicating that gaze control is an important part of social communication. Previous research on gaze control in a social context mainly focused on the gaze recipient by asking how humans respond to perceived gaze (gaze cueing). So far, this perspective has hardly considered the actor’s point of view by neglecting to investigate what mental processes are involved when actors decide to perform an eye movement to trigger a gaze response in another person. Furthermore, eye movements are also used to affect the non-social environment, for instance when unlocking the smartphone with the help of the eyes. This and other observations demonstrate the necessity to consider gaze control in contexts other than social communication whilst at the same time focusing on commonalities and differences inherent to the nature of a social (vs. non-social) action context. Thus, the present work explores the cognitive mechanisms that control such goal-oriented eye movements in both social and non-social contexts.
The experiments presented throughout this work are built on pre-established paradigms from both the oculomotor research domain and from basic cognitive psychology. These paradigms are based on the principle of ideomotor action control, which provides an explanatory framework for understanding how goal-oriented, intentional actions come into being. The ideomotor idea suggests that humans acquire associations between their actions and the resulting effects, which can be accessed in a bi-directional manner: Actions can trigger anticipations of their effects, but the anticipated resulting effects can also trigger the associated actions. According to ideomotor theory, action generation involves the mental anticipation of the intended effect (i.e., the action goal) to activate the associated motor pattern. The present experiments involve situations where participants control the gaze of a virtual face via their eye movements. The triggered gaze responses of the virtual face are consistent to the participant’s eye movements, representing visual action effects. Experimental situations are varied with respect to determinants of action-effect learning (e.g., contingency, contiguity, action mode during acquisition) in order to unravel the underlying dynamics of oculomotor control in these situations. In addition to faces, conditions involving changes in non-social objects were included to address the question of whether mechanisms underlying gaze control differ for social versus non-social context situations.
The results of the present work can be summarized into three major findings. 1. My data suggest that humans indeed acquire bi-directional associations between their eye movements and the subsequently perceived gaze response of another person, which in turn affect oculomotor action control via the anticipation of the intended effects. The observed results show for the first time that eye movements in a gaze-interaction scenario are represented in terms of their gaze response in others. This observation is in line with the ideomotor theory of action control. 2. The present series of experiments confirms and extends pioneering results of Huestegge and Kreutzfeldt (2012) with respect to the significant influence of action effects in gaze control. I have shown that the results of Huestegge and Kreutzfeldt (2012) can be replicated across different contexts with different stimulus material given that the perceived action effects were sufficiently salient. 3. Furthermore, I could show that mechanisms of gaze control in a social gaze-interaction context do not appear to be qualitatively different from those in a non-social context.
All in all, the results support recent theoretical claims emphasizing the role of anticipation-based action control in social interaction. Moreover, my results suggest that anticipation-based gaze control in a social context is based on the same general psychological mechanisms as ideomotor gaze control, and thus should be considered as an integral part rather than as a special form of ideomotor gaze control.
Virtual reality exposure therapy (VRET) is an effective cognitive-behavioral treatment for anxiety disorders that comprises systematic confrontations to virtual representations of feared stimuli and situations.
However, not all patients respond to VRET, and some patients relapse after successful treatment. One explanation for this limitation of VRET is that its underlying mechanisms are not yet fully understood, leaving room for further improvement.
On these grounds, the present thesis aimed to investigate two major research questions: first, it explored how virtual stimuli induce fear responses in height-fearful participants, and second, it tested if VRET outcome could be improved by incorporating techniques derived from two different theories of exposure therapy. To this end, five studies in virtual reality (VR) were conducted.
Study 1 (N = 99) established a virtual environment for height exposure using a Computer Automatic Virtual Environment (CAVE) and investigated the effects of tactile wind simulation in VR. Height-fearful and non-fearful participants climbed a virtual outlook, and half of the participants received wind simulation. Results revealed that height-fearful participants showed stronger fear responses, on both a subjective and behavioral level, and that wind simulation increased subjective fear. However, adding tactile wind simulation in VR did not affect presence, the user's sense of 'being there' in the virtual environment. Replicating previous studies, fear and presence in VR were correlated, and the correlation was higher in height-fearful compared to non-fearful participants.
Study 2 (N = 43) sought to corroborate the findings of the first study, using a different VR system for exposure (a head-mounted display) and measuring physiological fear responses. In addition, the effects of a visual cognitive distractor on fear in VR were investigated. Participants' fear responses were evident on both a subjective and physiological level---although much more pronounced on skin conductance than on heart rate---but the virtual distractor did not affect the strength of fear responses.
In Study 3 (N = 50), the effects of trait height-fearfulness and height level on fear responses were investigated in more detail. Self-rated level of acrophobia and five different height levels in VR (1 m--20 m) were used as linear predictors of subjective and physiological indices of fear. Results showed that subjective fear and skin conductance responses were a function of both trait height-fearfulness and height level, whereas no clear effects were visible for heart rate.
Study 4 (N = 64 + N = 49) aimed to advance the understanding of the relationship between presence and fear in VR. Previous research indicates a positive correlation between both measures, but possible causal mechanisms have not yet been identified. The study was the first to experimentally manipulate both presence (via the visual and auditive realism of the virtual environment) and fear (by presenting both height and control situations). Results indicated a causal effect of fear on presence, i.e., experiencing fear in a virtual environment led to a stronger sense of `being there' in the virtual environment. However, conversely, presence increased by higher scene realism did not affect fear responses. Nonetheless, presence seemed to have some effects on fear responding via another pathway, as participants whose presence levels were highest in the first safe context were also those who had the strongest fear responses in a later height situation. This finding indicated the importance of immersive user characteristics in the emergence of presence and fear in VR.
The findings of the first four studies were integrated into a model of fear in VR, extending previous models and highlighting factors that lead to the emergence of both fear and presence in VR. Results of the studies showed that fear responses towards virtual heights were affected by trait height-fearfulness, phobic elements in the virtual environment, and, at least to some degree, on presence. Presence, on the other hand, was affected by experiencing fear in VR, immersion---the characteristics of the VR system---and immersive user characteristics. Of note, the manipulations of immersion used in the present thesis, visual and auditory realism of the virtual environment and tactile wind simulation, were not particularly effective in manipulating presence.
Finally, Study 5 (N = 34) compared two different implementations of VRET for acrophobia to investigate mechanisms underlying its efficacy. The first implementation followed the Emotional Processing Theory, assuming that fear reduction during exposure is crucial for positive treatment outcome. In this condition, patients were asked to focus on their fear responses and on the decline of fear (habituation) during exposures. The second implementation was based on the inhibitory learning model, assuming that expectancy violation is the primary mechanism underlying exposure therapy efficacy. In this condition, patients were asked to focus on the non-occurrence of feared outcomes (e.g., 'I could fall off') during exposure. Based on predictions of the inhibitory learning model, the hypothesis for the study was that expectancy-violation-based exposure would outperform habituation-based exposure.
After two treatment sessions in VR, both treatment conditions effectively reduced the patients' fear of heights, but the two conditions did not differ in their efficacy. The study replicated previous studies by showing that VRET is an effective treatment for acrophobia; however, contrary to the assumption, explicitly targeting the violation of threat expectancies did not improve outcome. This finding adds to other studies failing to provide clear evidence for expectancy violation as the primary mechanism underlying exposure therapy. Possible explanations for this finding and clinical implications are discussed, along with suggestions for further research.
Adapting defensive behavior to the characteristics of a threatening situation is a fundamental function of the brain. Particularly, threat imminence plays a major role for the organization of defensive responses. Acute threat prompts phasic physiological responses, which are usually associated with an intense feeling of fear. In contrast, diffuse and potentially threatening situations elicit a sustained state of anxious apprehension. Detection of the threatening stimulus defines the key event in this framework, initiating the transition from potential to acute threat. Consequently, attention to threat is crucial for supporting defensive behavior. The functions of attention are finely tuned to the characteristics of a threatening situation. Potential threat is associated with hypervigilance, in order to facilitate threat detection. Once a threatening stimulus has been identified, attention is selectively focused on the source of danger. Even though the concepts of selective attention and hypervigilance to threat are well established, evidence for their neural correlates remain scarce. Therefore, a major goal of this thesis is to elucidate the neural correlates of selective attention to acute threat and hypervigilance during potential threat. A second aim of this thesis is to provide a mechanistic account for the interaction of fear and anxiety. While contemporary models view fear and anxiety as mutually exclusive, recent findings for the neural networks of fear and anxiety suggest potential interactions. In four studies, aversive cue conditioning was used to induce acute threat, while context conditioning served as a laboratory model of potential threat. To quantify neural correlates of selective attention and hypervigilance, steady-state visual evoked potentials (ssVEPs) were measured as an index of visuocortical responding. Study 1 compared visuocortical responses to acute and potential threat for high versus low trait-anxious individuals. All individuals demonstrated enhanced electrocortical responses to the central cue in the acute threat condition, suggesting evidence for the neural correlate of selective attention. However, only low anxious individuals revealed facilitated processing of the contexts in the potential threat condition, reflecting a neural correlate of hypervigilance. High anxious individuals did not discriminate among contexts. These findings contribute to the notion of aberrational processing of potential threat for high anxious individuals. Study 2 and 3 realized orthogonal combinations of cue and context conditioning to investigate potential interactions of fear and anxiety. In contrast to Study 1 and 2, Study 3 used verbal instructions to induce potentially threatening contexts. Besides ssVEPs, threat ratings and skin conductance responses (SCRs) were recorded as efferent indices of defensive responding. None of these studies found further evidence for the neural correlates of hypervigilance and selective attention. However, results for ratings and SCRs revealed additive effects of fear and anxiety, suggesting that fear and anxiety are not mutually exclusive, but interact linearly to organize and facilitate defensive behavior. Study 4 tested ssVEPs to more ecologically valid forms of context conditioning, using flickering video stimuli of virtual offices to establish context representations. Contrary to expectations, results revealed decreased visuocortical responses during sustained presentations of anxiety compared to neutral contexts. A disruption of ssVEP signals eventually suggests interferences by continuously changing video streams which are enhanced as a function of motivational relevance. In summary, this thesis provided evidence for the neural correlates of attention only for isolated forms of fear and anxiety, but not for their interaction. In contrast, an additive interaction model of fear and anxiety for measures of defensive responding offers a new perspective on the topography of defensive behavior.