Estimation of Detection Thresholds for Acoustic Based Redirected Walking Techniques Stefania Serafin ∗ Niels C. Nilsson † Erik Sikstrom ‡ Amalia De Goetzen § Rolf Nordahl ¶ Aalborg University Copenhagen A.C. Meyers Vaenge 15, 2450 Copenhagen, DK ABSTRACT We describe two psychophysical experiments where we have quan- tified how much humans can unknowingly be redirected by auditory stimuli. The experiments use a two-alternative-forced-choice task. We tested 19 subjects in two different experiments: (E1) discrimi- nation between virtual and physical rotation, and (E2) discrimina- tion of path curvature. In experiment E1 subjects performed ro- tations with different gains, and then had to choose whether the auditory perceived rotation was smaller or greater than the physi- cal rotation. In experiment E2 subjects estimate the path curvature when walking a curved path in the real world while the visual dis- play shows a straight path in the virtual world. Our results show that users can be turned physically about 20% percent more or 12% less than the perceived virtual rotation, and users can be redirected on a circular arc while they believe they are walking straight. Keywords: auditory feedback, redirected walking. 1 I NTRODUCTION The investigation of natural methods for simulating walking in vir- tual environments is an active research topic in the virtual reality (VR) community. Traveling through immersive virtual environ- ments by means of real walking is an important activity to increase naturalness of virtual reality (VR)-based interaction [7]. One ac- tive research direction consists of redirecting users [4]. One of the biggest problems faced by developers of immersive VR applica- tions is the potential discrepancy between the size of virtual and physical environments. If the physical environment is smaller than the virtual environment, this may hamper the user experience and even be dangerous. Redirected walking makes up one possible so- lution to this problem. Redirected walking has been mostly im- plemented using visual feedback, with auditory feedback used as distractors but without any formal evaluation of their possibilities [2]. In this paper we present a preliminary investigation on the role of auditory feedback for redirection. To achieve this goal, we adapted the experiments described in [5, 6], to be used only with auditory feedback. 2 EXPERIMENTAL SETUP We performed both experiments in a darkened room, where a sur- round sound system with 16 BM5A Dynaudio speakers was placed. The speakers were positioned at approximatively 1.60m from the floor, around a circle with a diameter of 7.1 meters. Subjects were asked to wear a nVisor SX head- mounted display (HMD), which ∗ e-mail: sts@create.aau.dk † e-mail:ncn@create.aau.dk ‡ e-mail:es@create.aau.dk § e-mail:ago@create.aau.dk ¶ e-mail: rn@create.aau.dk was turned off during the experiments. In both experiments, sub- jects were asked to navigate in a darkened room, where the only audible auditory feedback was an alarm clock sound played from different locations in the room. This sound was chosen since it was a sound emitted by an object that normally does not move. More- over, it made sense to hear the sound while being in a quiet and dark room. During the introduction subjects were asked to imagine exactly this scenario. The sound was delivered to the speakers and spatialized using the vector based amplitude panning (VBAP) algo- rithm. This algorithm allows to precisely place and move a sound in space [3]. 19 subjects (13 males and 6 females) participated in both exper- iments. They were aged between 19 and 32 years (mean = 24.6 years, standard deviation = 3.6). The two experiments lasted about 30 minutes, and subjects were rewarded with a movie ticket at the end. As done in [6], for both experiments we used the method of constant stimuli in a two-alternative forced-choice (2AFC) task. 3 EXPERIMENT 1: DISCRIMINATION BETWEEN VIRTUAL AND PHYSICAL ROTATION Figure 1: Results of the discrimination between virtual and physi- cal rotation. The x-axis shows the applied rotation gain, the y-axis shows the probability of estimating a virtual rotation smaller than the physical counterpart. In this experiment we investigated subjects’ ability to discrim- inate whether a physical rotation was smaller or greater than the simulated virtual rotation. Therefore, we instructed the subjects to rotate on a physical spot until a distinct alarm sound was perceived 161 IEEE Virtual Reality 2013 16 - 20 March, Orlando, FL, USA 978-1-4673-4796-9/13/$31.00 ©2013 IEEE