Larsen, Camilla Horne

Larsen, Jacob Junker

Lauritsen, David Skødt

Madsen, Jacob Boesen

Pilgaard, Marc

Stenholt, Rasmus

Due to increased computational power, reproducing binauralhearing in real-time applications, through usage of head-related transferfunctions (HRTFs), is now possible. This paper addresses the differencesin aurally-aided visual search performance between a HRTF enhancedaudio system (3D) and an amplitude panning audio system (panning) ina virtual environment. We present a performance study involving 33 participants locating aurally-aided visual targets placed at fixed positions,under different audio conditions. A varying amount of visual distractorswere present, represented as black circles with white dots. The resultsindicate that 3D audio yields faster search latencies than panning audio,especially with larger amounts of distractors. The applications of thisresearch could fit virtual environments such as video games or virtualsimulations

    Aalborg UniversitetAurally Aided Visual Search Performance Comparing Virtual Audio SystemsLarsen, Camilla Horne; Lauritsen, David Skødt; Larsen, Jacob Junker; Pilgaard, Marc;Madsen, Jacob Boesen; Stenholt, RasmusPublished in:Spatial Cognition IXPublication date:2014Document VersionEarly version, also known as pre-printLink to publication from Aalborg UniversityCitation for published version (APA):Larsen, C. H., Lauritsen, D. S., Larsen, J. J., Pilgaard, M., Madsen, J. B., & Stenholt, R. (2014). Aurally AidedVisual Search Performance Comparing Virtual Audio Systems. In C. Freksa, B. Nebel, M. Hegarty, & T.Barkowsky (Eds.), Spatial Cognition IX: SFB/TR 8 Report No. 036-09/2014 (Vol. 8684, pp. 70-73). Bremen,Germany: SFB/TR 8.General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            ? Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            ? You may not further distribute the material or use it for any profit-making activity or commercial gain            ? You may freely distribute the URL identifying the publication in the public portal ?Take down policyIf you believe that this document breaches copyright please contact us at vbn@aub.aau.dk providing details, and we will remove access tothe work immediately and investigate your claim.Downloaded from vbn.aau.dk on: May 01, 2017Aurally Aided Visual Search PerformanceComparing Virtual Audio SystemsCamilla H. Larsen, David S. Lauritsen, Jacob J. Larsen, Marc Pilgaard,Jacob B. Madsen & Rasmus StenholtSchool of Information and Communication Technology, Aalborg University, Denmark{clarse10, dlauri10, jjla10, mpilga10}@student.aau.dk, {jbm, rs}@create.aau.dkAbstract. Due to increased computational power, reproducing binauralhearing in real-time applications, through usage of head-related transferfunctions (HRTFs), is now possible. This paper addresses the differencesin aurally-aided visual search performance between a HRTF enhancedaudio system (3D) and an amplitude panning audio system (panning) ina virtual environment. We present a performance study involving 33 par-ticipants locating aurally-aided visual targets placed at fixed positions,under different audio conditions. A varying amount of visual distractorswere present, represented as black circles with white dots. The resultsindicate that 3D audio yields faster search latencies than panning audio,especially with larger amounts of distractors. The applications of thisresearch could fit virtual environments such as video games or virtualsimulations.Keywords: Visual search, binaural audio, virtual environments, spatialaudio, aurally aid, localization performance1 IntroductionSpatial audio is an important feature in virtual environments as it helps usersorient themselves, and can provide 360 aural awareness, independently of sight.Previously, the possibility of more closely simulating binaural hearing in real-time was constrained by hardware performance. Even though typical hardwarecan handle the processing task today, still only few applications utilize this tech-nology and instead a simple stereo amplitude panning method is used.Prior to this study, we did an audio exclusive localization experiment, theresults of which suggest that binaurally simulated sound (3D sound) improveslocalization performance, compared to amplitude-panned sound (panning sound)[1].The comparison between 3D sound and panning sound in this study is ex-clusive to virtual environments and includes visual stimuli.Our hypothesis is this: there is a significant difference in search latencies inaurally aided visual search, between using a panning- and a 3D audio system.2 Larsen et al.2 Experiment designIn this experiment, the participant had to locate a visual object within a vir-tual environment with changing audio- and visual conditions for each trial. Theparticipant’s task was to locate a visual target among a set of visual distractors,using a mouse to manipulate the virtual camera view. The experiment consistedof two independent variables: audio condition and amount of distractors. Theaudio condition consisted of three levels: no audio, panning audio and 3D audio.The amount of distractors consisted of eight levels: 0, 2, 4, 8, 16, 32, 64 or 128.Before each trial a countdown appeared, counting from three to zero, whichindicated when the participant could begin. When the participant had locatedthe target, he was required to aim at the target with an on-screen cross-hair andperform a mouse click within the stimuli’s bounds. If the participant hit the tar-get, the system took control of the virtual camera and panned it to its startingposition. The countdown appeared again, and the next trial began. Each partici-pant went through 144 different trials, hence 48 trials for each audio condition, 6for each amount of distractors. The order of audio rendering conditions followeda 3x3 Latin square design. The experiment was conducted as a within subjectexperiment.The auditory stimuli used was 700 ms bursts of pink noise at a fixed audiblelevel, with a silence period of 700 ms. The pink noise stimuli had 100 ms of linearfade, both in and out, leaving 500 ms at full intensity.The visual stimuli used was a black circle with white dots in the middle.The black circle’s visual angle was 4.7◦ of the virtual camera view. The targetobject was a black circle with an odd amount (one or three) of white dots inside,while the distractors had an even amount (two or four). The stimuli were alsorandomly rotated at 90◦ steps.Fig. 1. Two depictions from the virtual environment. The image to the left shows athe setup of the environment with the virtual character in the center and 129 instances(note that the backfacing visuals cannot be seen) of visual stimuli distributed on thevertices of the icosahedron. The highlighted area represents the visual field. The imageto the right is an example of how the screen could appear to a subject.The positions of both the target and distractors were based on the verticesof a icosahedron, with 6 m in diameter. It was subdivided three times, resultingAurally Aided Visual Search Performance Comparing Virtual Audio Systems 3in 162 available points. The distractors and the target were placed at randomdiscrete positions, each at one of the 162 available positions. There was only onetarget per trial. The amount of distractors for each trial was chosen through fixedrandomization, assuring balance across all conditions. All stimuli were facing theparticipant’s avatar at all time. The virtual settings was inside a box, the sidesof which were dimly lit by yellow light. This was to provide participants with asense of orientation. See figure 1 for a visual example of how one set might look.The participant’s avatar was in the center of the icosahedron, with a distance of3 m to every point.3 Results and DiscussionA significant difference in search latencies was identified between the differentaudio conditions independent of distractor amount (Friedman test, p < 0.001)being x¯ = 9.798 seconds for the no audio condition, x¯ = 3.588 seconds for the3D audio condition and x¯ = 4.985 seconds for the panning audio condition.There was also a significant difference in search latencies with an increasedamount of distractors (Friedman test, p < 0.001). Figure 2 illustrates the differentcombinations of audio conditions and distractor amounts and their significancelevel to each other. The linear increase in search latencies at increased distractoramounts suggests that the search task was not affected by preattentive search.0      2      4      8     16    32    64   128NonePanning3DSlowestFastestDistractor amountAudio conditionFig. 2. The significance levels between combinations of audio conditions and amountsof distractors. White represents the combinations with the fastest search latency, redrepresents the slowest. Squares of different color are of a significant difference. Squareswith two colors are of no significant difference to both identically colored whole squares.Different starting positions for the target also created a significant difference(Friedman test, p < 0.001). If the target stimuli was placed at a vertical po-sition exceeding 30◦ in the vertical plane relative the participant’s initial lookdirection (making it not visible from the start) the participant would have tosearch through the vertical plane in order to reveal the target. These conditionsincreased the search latencies significantly (Friedman test, p < 0.05) with 0.802seconds for the 3D audio condition and 2.194 seconds for the panning audiocondition.The accumulated time each participant had the target within their FOV,when fully visible, was also recorded. There was a significant difference (Friedman4 Larsen et al.test, p < 0.001) in time, with mean values of x¯= 1.932 seconds, x¯= 1.603 secondsand x¯ = 1.451 seconds respectively for the no audio, panning audio and 3D audioconditions. This could be due to adaptive behavior, as the participant relies onaudio for an early orientation cue. Typical orientation through binaural hearingis helped by moving the head and listening, potentially explaining the result.The data indicates that there was a significant difference in search latenciesbetween using the two different stimuli (Friedman test, p = 0.003) with meanlatencies of x¯ = 7.0 seconds for the three dotted stimuli and x¯ = 5.347 secondsfor the single dotted stimuli. The significant difference in latencies between thetwo visual target stimuli suggests that they were not equally susceptible to visualattention. Based on the works of Pomerantz and Cragin [3] we believe this isdue to differences in emerging features. Both distractors and the three dot targetstimuli contain more than two black dots, therefore emerging features such asproximity and orientations between the two or more points is present. The singledot stimuli can not have these features, except its positional feature from itssingle dot. This makes it stand out, and so, it becomes a Gestalt, leading it toemerge from the field of distractors. This can lead to faster acquisition times.We believe this did not have a great impact on our experiments results due tothe within-subject design.4 ConclusionThe results show that using 3D audio compared to panning audio decreasessearch latencies significantly (by 28%), confirming previous studies [2]. Further-more, with increasing amount of visual distractors, 3D audio reduces searchlatencies compared to panning audio. This suggests that the visual distractorsaffect search performance, across all audio conditions. Search latencies were sig-nificantly decreased, by 9.5%, for 3D audio compared to panning audio, evenwith the visual stimuli being within the field of view, suggesting that auditorystimuli is used as an aid to visual search even within the field of view. The twovisual stimuli gave significantly different search times, where the single-dot stim-uli elicited faster search than the three-dot stimuli, which implies that our visualstimuli were not equal.References1. C. H. Larsen, D. S. Lauritsen, J. J. Larsen, M. Pilgaard, and J. B. Madsen. Differ-ences in human audio localization performance between a HRTF- and a non-HRTFaudio system. 2013.2. J. P. McIntire, P. R. Havig, S. N. J. Watamaniuk, and R. H. Gilkey. Visual searchperformance with 3-d auditory cues: Effects of motion, target location, and prac-tice. Human Factors: The Journal of the Human Factors and Ergonomics Society,52(1):41–53, Feb. 2010.3. J. Pomerantz and A. Cragin. Emergent features and feature combination. OxfordHandbook of Perceptual Organization, To be published.

Aurally Aided Visual Search Performance Comparing Virtual Audio Systems

Due to increased computational power reproducing binaural hearing in real-time applications, through usage of head-related transfer functions (HRTFs), is now possible. This paper addresses the differences in aurally-aided visual search performance between an HRTF enhanced audio system (3D) and an amplitude panning audio system (panning) in a virtual environment. We present a performance study involving 33 participants locating aurally-aided visual targets placed at fixed positions, under different audio conditions. A varying amount of visual distractors were present, represented as black circles with white dots. The results indicate that 3D audio yields faster search latencies than panning audio, especially with larger amounts of distractors. The applications of this research could fit virtual environments such as video games or virtual simulations

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Aurally Aided Visual Search Performance Comparing Virtual Audio Systems

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