Effects of anxiety on perceptual biases for ambiguous biological motion stimuli

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Heenan, Adam
perception , vision , biological motion perception , anxiety
Biological motion stimuli, depicted as orthographically projected point-light or stick-figure walkers, do not contain any information about their orientation in depth. The projections of such stimuli, therefore, provide the same visual information when oriented towards the viewer as when oriented away. Even though this is the case, naïve observers display a bias to perceive the facing-towards percept more often. Some researchers have speculated that this facing-the-viewer bias may exist for sociobiological reasons. That is, mistaking another human as retreating when they are actually approaching could potentially have more severe consequences than the opposite error. This theory implies that the facing-towards percept of a biological motion stimulus is potentially more threatening. Measures of anxiety and the facing-the-viewer bias should therefore be related, as researchers have consistently found that anxious individuals display an attentional bias towards more threatening stimuli. In our first experiment, we demonstrated that individuals with greater anxiety do indeed have greater facing-the-viewer biases, and that this relationship is mediated by inhibitory ability (Chapter 2). As our first experiment was correlational in nature, we next used a between-subjects design. We showed that physical exercise, which is known to reduce anxiety, also reduces the facing-the-viewer bias for full stick figure walkers, but not for bottom- or top-half-only stimuli (Chapter 3). In our final experiment, we manipulated anxiety more directly using progressive muscle relaxation and an anxiety induction task (Chapter 4). In the latter experiment, we found that relaxation had the same effect on facing-the-viewer biases that physical exercise had, while our anxiety induction task did not affect biases significantly. In Chapter 6, we discuss the importance of these findings in the context of understanding how anxiety affects our perception of our external environment.
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