Asymmetries in behavioral and neural responses to spectral cues demonstrate the generality of auditory looming bias

Abstract

Studies of auditory looming bias have shown that sources increasing in intensity are more salient than sources decreasing in intensity. Researchers have argued that listeners are more sensitive to approaching sounds compared with receding sounds, reflecting an evolutionary pressure. However, these studies only manipulated overall sound intensity; therefore, it is unclear whether looming bias is truly a perceptual bias for changes in source distance, or only in sound intensity. Here we demonstrate both behavioral and neural correlates of looming bias without manipulating overall sound intensity. In natural environments, the pinnae induce spectral cues that give rise to a sense of externalization; when spectral cues are unnatural, sounds are perceived as closer to the listener. We manipulated the contrast of individually tailored spectral cues to create sounds of similar intensity but different naturalness. We confirmed that sounds were perceived as approaching when spectral contrast decreased, and perceived as receding when spectral contrast increased. We measured behavior and electroencephalography while listeners judged motion direction. Behavioral responses showed a looming bias in that responses were more consistent for sounds perceived as approaching than for sounds perceived as receding. In a control experiment, looming bias disappeared when spectral contrast changes were discontinuous, suggesting that perceived motion in distance and not distance itself was driving the bias. Neurally, looming bias was reflected in an asymmetry of late eventrelated potentials associated with motion evaluation. Hence, both our behavioral and neural findings support a generalization of the auditory looming bias, representing a perceptual preference for approaching auditory objects.auditory looming bias | electroencephalography | distance motion perception | sound externalization | head-related transfer functions I magine yourself alone in the wilderness. Suddenly, a threatening sound permeates the darkness. Is it approaching? This is a critical question when it comes to your survival because approaching objects usually pose a greater threat than receding objects (1). The phenomenon that approaching sounds are more salient than receding sounds is commonly termed "auditory looming bias." Looming bias is reflected in a broad variety of psychophysical tasks related to salience and alertness: bias in loudness-change estimates (2-4) and judgments of duration (5), improved discriminability of motion speed (6), underestimated distances for egocentrically moving (4) or bypassing sounds (7,8), and reduced reaction time for auditory (3, 9) and visual (3) targets preceded by looming sounds. In animals, looming biases result in faster learning speed during associative conditioning (10) and longer duration of attention (11). This list shows that looming bias triggers a variety of percepts across a wide range of psychoacoustic tasks. Despite its broad behavioral significance, the mechanisms underlying auditory looming bias are still poorly ...

Decision making in auditory externalization perception: model predictions for static conditions

“…We first investigated the ability of each individual cue to explain the effects of signal manipulations on auditory externalization as tested in five previous headphone experiments (Baumgartner et al, 2017;Boyd et al, 2012;Hartmann & Wittenberg, 1996;Hassager et al, 2016). Figure 2 shows the simulated externalization ratings together with the actual ratings replotted from the corresponding experiments with normalized rating scales.…”

“…The fourth experiment also tested the effect of spectral smoothing (Baumgartner et al, 2017), however, focusing on the high-frequency range from 1 kHz to 16 kHz, where the pinnae induce the most significant directional spectral variations. There, listeners were presented to noise stimuli being spectrally flat (C = 0), spectrally shaped according to their individual acoustics (C = 1), or something in between (C = 0.5).…”

“…The spatial properties of the sound arriving at the two ears are manifold and so are the cues that can be used for spatial inference . Many studies aimed to identify in particular spectral cues affecting the perceptual externalization of sound sources (Baumgartner et al, 2017;Boyd et al, 2012;Hartmann & Wittenberg, 1996;Hassager et al, 2016;Zhang & Hartmann, 2010). These cues can be grouped into two categories (Tab.…”

“…, into a single-cue expectation error, d cue , 2) stages mapping that single-cue error to a normalized externalization rating, e cue , and 3) a decision stage combining the single-cue based ratings into the final externalization rating, E. We used that framework to simulate five experiments from representative psychoacoustic externalization studies (Baumgartner et al, 2017;Boyd et al, 2012;Hartmann & Wittenberg, 1996;Hassager et al, 2016), all focusing on the effects of spectral distortions under static listening conditions, but differing considerably in manipulation method and bandwidth. The listener's expectations for perceptual inference are represented as internal templates and used for comparison with incoming cue-specific information, distinguishing between processing monaural and interaural cues (Fig.…”

Impoverished auditory cues fail to engage brain networks controlling spatial selective attention

“…When only isolated or impoverished spatial cues are present, auditory localization performance degrades 45 and the natural perception of external auditory objects may even collapse into the listener's head 46 (Baumgartner et al, 2017;Callan et al, 2013;Cubick et al, 2018;Hartmann and Wittenberg, 1996). 47…”