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19th INTERNATIONAL CONGRESS ON ACOUSTICS

MADRID, 2-7 SEPTEMBER 2007

Perceiving Looming Sounds:The Importance of Auditory Motion as a Sound Source Property

Neuhoff, John, G.The College of Wooster, Wooster, OH 44691, USA; [email protected]

ABSTRACTOne critically important environmental property of a sound source is its physical location inspace. The distance between a sound source and a listener is a critical factor shaping neural,physiological, and behavioural responses to sound sources. Specifically, sound sources that areapproaching a listener (looming sources) initiate responses in neural populations that mediateattention to auditory space, assignment of appropriate responses, and even motor planning inresponse to looming sound sources. Analogous neural activity does not occur in response toreceding sound sources. Physiological responses such as heart rate and galvanic skinresponse show similar differentiation between looming and receding sounds. Finally,

behavioural responses to looming sources indicate a perceptual bias to hear sound sources ascloser than actual and to underestimate the arrival time of a looming source. Taken together,these findings indicate the environmental salience of looming sound sources and demonstratean important link between perception of a sound source and the potential to physically interactwith the source. These findings provide indirect evidence that suggests the perceptualanisotropy in the perception of looming and receding sounds may be advantageous inevolutionary terms.

PERCEIVING SOUND SOURCES AND SOUND SOURCE PROPERTIESBecause of the relatively sparse history of investigating the perception of sound sourceproperties, there is still little consensus over the precise terminology that should be used todescribe the perception of sound sources. For example, when describing a sound, someresearchers have developed entire theoretical paradigms around the term auditory object [1].Others prefer the term auditory event to describe very similar auditory phenomena [2]. Still

others have taken a slightly different approach to defining auditory objects and grappled with thevery basic question What is an auditory object? [3]. Nonetheless, the intent of many recentinvestigations into the perception of sound source properties has been to shift the traditionalfocus on the perception of the acoustic characteristics of the sound per se (such as pitch andloudness), to the perception of the physical properties of the object that is producing the sound(such as weight, shape, or size [4]).

Sound source properties and spatial locationMuch of the work on the perception of sound source properties stems from the now classicpapers by Gaver which proposed an innovative way of thinking about what and how we hear[5, 6]. The thrust of Gavers work suggested that in everyday listening situations, people dontattend to pitch or timbre, or other acoustic properties of sound energy. Rather, they identifysound sources and the physical properties of objects that are producing sound. Gaversuggested that sound events could be divided into three main categories based on the physical

properties of the objects that created the sound- solid, liquid, or gas. More complex soundscould be created by interactions between these main three categories.

Although the physical materials that make up a sound source are fundamental to the perceptionof sound source properties, the location of the sound source relative to the listener is also acrucial property of a sounding object. Any object, be it auditory or visual, must occur at alocation in space. Thus, spatial location is an inherent property of objects (or events). Generallyspeaking, the closer a sound source is to a listener, the more salient and ecologically relevantthat source becomes. When sound sources are moving, those that are approaching a listener(or looming) are generally treated with greater urgency than those that are receding.

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INTERNATIONAL CONGRESS ON ACOUSTICS ICA2007MADRID

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LOOMING SOUND OBJECTSA typical methodology that has been used to investigate the perception of looming soundsrequires subjects to estimate the arrival time of a sound source that is approaching the listeningpoint. Subjects are asked to press a key when they think that the sound source will havereached the arrival position. A consistent finding in these Time-to-Arrival studies is thatlisteners generally underestimate time-to-arrival, judging the source to have arrived sooner than

it actually does [7-11].

Guski [12] has suggested that this anticipatory bias reflects a characteristic of the auditorysystem that allows for advanced warning of looming objects. He suggested that accurate timeto arrival estimation is not the function of auditory localization. Rather, the auditory systemprovides input on a categorical judgment about whether there is time to direct the visual systemtoward the looming source or whether evasive actions should be initiated by the motor system.In essence, Guski suggested that this categorical decision about directing the visual system ismore important than precise auditory-time-to-arrival estimation. Neuhoff [13] further suggestedthat the advanced warning provided by the auditory system might be rooted in an evolutionaryadaptation. If listeners perceive a looming sound source as closer than it actually is, then theywould have slightly more time than expected to prepare for the sources arrival. This additionalpreparation time might provide a selective advantage. Several lines of evidence have supportedthis assertion.

Neural and physiological evidenceIf Guskis speculation about the auditory system providing input into a decision about whetherthe listener has time to turn and look toward the looming object or must immediately initiateevasive motor actions, then we might expect looming sounds to preferentially activate motorplanning areas in the brain. Recent neuroimaging work has borne out this prediction. Whenlisteners are presented with both looming and receding sounds, looming sounds preferentiallyactivate brain areas responsible for the perception of auditory space, stimulus discriminationand assignments of required responses, and (most critically) the integration of perception withmotor planning [14] (See Figure 1).

Figure 1. The general linear contrast looming versus receding tones yields a neural networkcomprising bilaterally the superior temporal sulci and the middle temporal gyri, the righttemporoparietal junction encompassing the inferior portion of the angular gyrus, the right motorand lateral premotor cortices mainly on the right hemisphere, the left frontal operculum ( FromSeiftitz, et al., 2002).

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More recent work has shown preferential neural, physiological, and behavioural orientingresponses to looming sounds over receding sounds. Physiological results showed orientingresponses in the form of differential changes in heart rate and skin conductance whenpresented with looming and receding sounds [15] (See Figure 2). Similar behavioural orientingresponses have been shown with Rhesus monkeys [16]. From the perspective of perceivingsound source properties, these data demonstrate the salience of looming sounds overequivalent receding or stationary sound sources.

Figure 2. Orienting reflex (heart rate and skin conductance response, mean SEM) inresponse to looming (open circles), receding (black circles), and constant (gray circles). *p

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cause listeners to underestimate its distance. However, similar decreases in intensity do notcause overestimation of distance. [18].

Perceived terminal position of approaching and

receding sound sources

0

10

20

30

40

Towa rd AwayDirection of travel

(with respect to listener)

Distancefroml

istener(ft.)

Tone

Noise

Actual terminal position

Figure 3. Perceived terminal position of approaching (toward) and receding (away) soundsources. Approaching sources are perceived as stopping closer than equidistant recedingsources. Tones are perceived as closer than equidistant noise. Distance estimates were madeby blind walking (From Neuhoff, 2001).

CONCLUSIONS

Any object or event must occur at a location in space. Thus, spatial location is an inherentproperty of auditory objects and events. Behavioural, neurological and physiological evidenceall converges on the finding that looming sound sources are environmentally salient stimuli thatare preferentially allocated perceptual and attentional resources when compared with equivalentstationary or receding sounds. Taken together, these findings indicate an important linkbetween perception of a sound source and the potential to physically interact with the source.These findings provide indirect evidence that suggests the perceptual anisotropy in theperception of looming and receding sounds may be advantageous in evolutionary terms.

References:

[1] D. Van Valkenburg and M. Kubovy, "From Gibson's fire to Gestalts: A bridge building theory ofperceptual objecthood," in Ecological Psychoacoustics, J. G. Neuhoff, Ed. San Diego, CA:Elsevier, 2004, pp. 113-147.

[2] L. D. Rosenblum, "Perceiving articulatory events: lessons for an ecological psychoustics," inEcological Psychoacoustics, J. G. Neuhoff, Ed. San Diego, CA: Elsevier, 2004, pp. 219-248.

[3] T. D. Griffiths and J. D. Warren, "What is an auditory object," Nature Reviews Neuroscience, vol.5, pp. 887-892, 2004.

[4] S. Lakatos, S. McAdams, and R. Causse, "The representation of auditory source characteristics:Simple geometric form.," Perception & Psychophysics, vol. 59, pp. 1180-1190, 1997.

[5] W. W. Gaver, "How do we hear in the world? Explorations in ecological acoustics," EcologicalPsychology, vol. Vol 5, pp. 285-313, 1993.

[6] W. W. Gaver, "What in the world do we hear? An ecological approach to auditory eventperception," Ecological Psychology, vol. Vol 5, pp. 1-29, 1993.

[7] L. D. Rosenblum, "Acoustical information for controlled collisions," in Contributions toPsychological Acoustics VI: Results of the Sixth Oldenburg Symposium on PsychologicalAcoustics, A. Shick, Ed. Oldenburg; Germany: BIS, 1993.

[8] L. D. Rosenblum, C. Carello, and R. E. Pastore, "Relative effectiveness of three stimulusvariables for locating a moving sound source," Perception, vol. 162, pp. 175-186, 1987.

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[9] L. D. Rosenblum, M. S. Gordon, and A. P. Wuestefeld, "Effects of performance feedback andfeedback withdrawal on auditory looming perception.," Ecological Psychology, vol. 12, pp. 273-291, 2000.

[10] L. D. Rosenblum, A. P. Wuestefeld, and H. M. Saldana, "Auditory looming perception: Influenceson anticipatory judgments," Perception, vol. 22, pp. 1467-1482, 1993.

[11] W. Schiff and R. Oldak, "Accuracy of judging time to arrival: Effects of modality, trajectory, andgender," Journal of Experimental Psychology Human Perception and Performance, vol. 16, pp.303-316, 1990.

[12] R. Guski, "Acoustic tau: An easy analogue to visual tau?," Ecological Psychology, vol. 4, pp. 189-197, 1992.[13] J. G. Neuhoff, "Perceptual bias for rising tones," Nature, vol. 395, pp. 123-124, 1998.[14] E. Seifritz, J. G. Neuhoff, D. Bilecen, D. Scheffler, H. Mustovic, H. Schchinger, R. Elefante, and

F. Di Salle, "Neural processing auditory 'looming' in the human brain," Current Biology, vol. 12,pp. 2147-2151, 2002.

[15] D. R. Bach, H. Schchinger, J. G. Neuhoff, F. Esposito, F. Di Salle, C. Lehmann, M. Herdener, K.Scheffler, and E. Seifritz, "Rising sound intensity as an intrinsic warning cue," Cerebral Cortex,pp. doi:10.1093/cercor/bhm040, 2007.

[16] A. A. Ghazanfar, J. G. Neuhoff, and N. K. Logothetis, "Auditory looming perception in rhesusmonkeys," Proceedings of the National Academy of Sciences USA, vol. 99, pp. 15755-15757,2002.

[17] J. G. Neuhoff, "An adaptive bias in the perception of looming auditory motion," EcologicalPsychology, vol. 13, pp. 87-110, 2001.

[18] D. H. Ashmead, D. L. Davis, and A. Northington, "Contribution of listeners' approaching motion toauditory distance perception," Journal of Experimental Psychology: Human Perception and

Performance, vol. Vol 21, pp. 239-256, 1995.

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