A Systematic Examination of Listener Experiences During the Shepard-Risset Glissando: Auditory Vection, Motion Sickness, Postural Activity, and Emotional Arousal

<p dir="ltr">The Shepard-Risset glissando (SRG) is an auditory illusion of pitch discrimination that produces an infinitely falling or rising sound that paradoxically never gets any higher or lower. Anecdotal reports have suggested that the SRG can evoke a range of sensations and symptoms in listeners; from feelings of falling, disrupted equilibrium, disorientation, nausea, and emotional arousal. This thesis aimed to establish an objective foundation for these anecdotal claims for the first time by systematically investigating these reported listener experiences. The experiment outlined in Chapter 2 aimed to identify the origins of the auditory illusions of self-motion (vection) and motion sickness induced by SRG. We found that the metaphorical auditory vection induced by the SRG was stronger than the other auditory controls tested, and the stepwise Shepard scale. However, vection strength was not found to differ between the multi-tonal SRG and the single toned auditory sweep signal. This suggests that the continuous, gliding pitch of both these auditory stimuli was integral to the induction of vection. Consistent with anecdotal reports that the SRG is also capable of generating motion sickness; the likelihood and severity of sickness for these stimuli was found to increase with the strength of the auditory vection. The experiment outlined in Chapter 3 re-examined vection while continuously measuring the postural responses induced by SRG while standing. As expected, vection was again found to be stronger during SRG than the other auditory control stimuli. Individual differences in spontaneous postural instability (observed before sound) and auditorily-induced sway (observed during the sound) were both found to predict the strength of this vection. The patterns of sway induced by SRG also differed significantly from those during our auditory control stimuli, but only in terms of their temporal dynamics. Chapter 4 presents two experiments investigating vection and emotional arousal in response to the SRG in terms of: (1) its intensity (skin conductance); and (2) its valence (pleasant/unpleasant). The first experiment confirmed that: (1) the presence of sound increased overall arousal levels (compared to no sound); (2) the amount of arousal increased with the strength of vection (for all sound types tested); and (3) the SRG elicited a distinct physiological response from the other sounds before vection onset. The second experiment revealed that: (4) while all five sounds were perceived to be unpleasant, listener experiences were generally less negative during the SRG; and (5) the degree of unpleasantness was also related to their experiences of vection (positive) and motion sickness (negative). Taken together these findings showed that SRG are capable of reliably inducing illusions of self-motion in participants. Also, the experience of vection appears to be related to individual differences in motion-sickness susceptibility, postural activity and both the intensity and valence of emotional arousal during listening. This research carries significant theoretical and applied implications for understanding self-motion perception, postural stability, music psychology, and sound design, and may practically inform the creation of more immersive multimedia user experiences (such as in VR) and developing sound-based therapies for emotional regulation.</p>