Dynamic spectral cues do not affect human sound localization during small head movements

Sound localization in noisy contexts: performance, metacognitive evaluations and head movements

Localizing sounds in noisy environments can be challenging. Here, we reproduce real-life soundscapes to investigate the effects of environmental noise on sound localization experience. We evaluated participants' performance and metacognitive assessments, including measures of sound localization effort and confidence, while also tracking their spontaneous head movements. Normal-hearing participants (N = 30) were engaged in a speech-localization task conducted in three common soundscapes that progressively increased in complexity: nature, traffic, and a cocktail party setting. To control visual information and measure behaviors, we used visual virtual reality technology. The results revealed that the complexity of the soundscape had an impact on both performance errors and metacognitive evaluations. Participants reported increased effort and reduced confidence for sound localization in more complex noise environments. On the contrary, the level of soundscape complexity did not influence the use of spontaneous exploratory head-related behaviors. We also observed that, irrespective of the noisy condition, participants who implemented a higher number of head rotations and explored a wider extent of space by rotating their heads made lower localization errors. Interestingly, we found preliminary evidence that an increase in spontaneous head movements, specifically the extent of head rotation, leads to a decrease in perceived effort and an increase in confidence at the single-trial level. These findings expand previous observations regarding sound localization in noisy environments by broadening the perspective to also include metacognitive evaluations, exploratory behaviors and their interactions.

Auditory vertical localization in the median plane with conflicting dynamic interaural time difference and other elevation cues

Both dynamic variation of interaural time difference (ITD) and static spectral cues provide information for front-back discrimination and vertical localization. However, the contributions of the two cues are still unclear. The static spectral cue has conventionally been regarded as the dominant one. In the present work, psychoacoustic experiments were conducted to examine the contribution of dynamic ITD and static spectral cues to vertical localization in the median plane. By modifying the head-related transfer functions used in a dynamic virtual auditory display, binaural signals with conflicting dynamic ITD and spectral cues that were either static or dynamically modified according to instantaneous head position were created. The results indicated that the dynamic ITD and static spectral cues contribute to vertical localization at low and high frequencies, respectively. For full a bandwidth stimulus, conflicting dynamic ITD and static spectral cues usually result in two separated virtual sources at different elevations corresponding to the spatial information conveyed by the low- and high-frequency bands, respectively. In most cases, no fused localization occurs in the high-level cognition system. Therefore, dynamic ITD and static spectral cues contribute to vertical localization at different frequency ranges, and neither of them dominates vertical localization in the case of wideband stimuli.

Head movement and its relation to hearing

Head position at any point in time plays a fundamental role in shaping the auditory information that reaches a listener, information that continuously changes as the head moves and reorients to different listening situations. The connection between hearing science and the kinesthetics of head movement has gained interest due to technological advances that have increased the feasibility of providing behavioral and biological feedback to assistive listening devices that can interpret movement patterns that reflect listening intent. Increasing evidence also shows that the negative impact of hearing deficits on mobility, gait, and balance may be mitigated by prosthetic hearing device intervention. Better understanding of the relationships between head movement, full body kinetics, and hearing health, should lead to improved signal processing strategies across a range of assistive and augmented hearing devices. The purpose of this review is to introduce the wider hearing community to the kinesiology of head movement and to place it in the context of hearing and communication with the goal of expanding the field of ecologically-specific listener behavior.