Certain, but incorrect: on the relation between subjective certainty and accuracy in sound localisation

Spatial hearing training in virtual reality with simulated asymmetric hearing loss

Sound localization is essential to perceive the surrounding world and to interact with objects. This ability can be learned across time, and multisensory and motor cues play a crucial role in the learning process. A recent study demonstrated that when training localization skills, reaching to the sound source to determine its position reduced localization errors faster and to a greater extent as compared to just naming sources' positions, despite the fact that in both tasks, participants received the same feedback about the correct position of sound sources in case of wrong response. However, it remains to establish which features have made reaching to sound more effective as compared to naming. In the present study, we introduced a further condition in which the hand is the effector providing the response, but without it reaching toward the space occupied by the target source: the pointing condition. We tested three groups of participants (naming, pointing, and reaching groups) each while performing a sound localization task in normal and altered listening situations (i.e. mild-moderate unilateral hearing loss) simulated through auditory virtual reality technology. The experiment comprised four blocks: during the first and the last block, participants were tested in normal listening condition, while during the second and the third in altered listening condition. We measured their performance, their subjective judgments (e.g. effort), and their head-related behavior (through kinematic tracking). First, people's performance decreased when exposed to asymmetrical mild-moderate hearing impairment, more specifically on the ipsilateral side and for the pointing group. Second, we documented that all groups decreased their localization errors across altered listening blocks, but the extent of this reduction was higher for reaching and pointing as compared to the naming group. Crucially, the reaching group leads to a greater error reduction for the side where the listening alteration was applied. Furthermore, we documented that, across blocks, reaching and pointing groups increased the implementation of head motor behavior during the task (i.e., they increased approaching head movements toward the space of the sound) more than naming. Third, while performance in the unaltered blocks (first and last) was comparable, only the reaching group continued to exhibit a head behavior similar to those developed during the altered blocks (second and third), corroborating the previous observed relationship between the reaching to sounds task and head movements. In conclusion, this study further demonstrated the effectiveness of reaching to sounds as compared to pointing and naming in the learning processes. This effect could be related both to the process of implementing goal-directed motor actions and to the role of reaching actions in fostering the implementation of head-related motor strategies.

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.

Instant improvement in monaural spatial hearing abilities through cognitive feedback

Several studies report that sound localization performance of acute and chronic monauralized normal-hearing listeners can improve through training. Typically, training sessions are administered daily for several days or weeks. While this intensive training is effective, it may also be that monaural localization abilities improve instantly after providing explicit top-down information about the direction dependent change in timbre and level. The aim of the present study was to investigate whether cognitive feedback (i.e., top-down information) could instantly improve sound localization in naive acutely monauralized listeners. Forty-three normal-hearing listeners (experimental group), divided over five different centers, were tested. Two control groups, consisting of, respectively, nine and eleven normal-hearing listeners, were tested in one center. Broadband sounds (0.5-20 kHz) were presented from visible loudspeakers, positioned in azimuth (- 90° to 90°). Participants in the experimental group received explicit information about the noticeable difference in timbre and the poor localization in the monauralized listening condition, resulting in an instant improvement in sound localization abilities. With subsequent roving of stimulus level (20 dB), sound localization performance deteriorated immediately. The reported improvement is related to the context of the localization test. The results provide important implications for studies investigating sound localization in a clinical setting, especially during closed-set testing, and indicate the importance of top-down information.

Orienting Auditory Attention through Vision: the Impact of Monaural Listening

The understanding of linguistic messages can be made extremely complex by the simultaneous presence of interfering sounds, especially when they are also linguistic in nature. In two experiments, we tested if visual cues directing attention to spatial or temporal components of speech in noise can improve its identification. The hearing-in-noise task required identification of a five-digit sequence (target) embedded in a stream of time-reversed speech. Using a custom-built device located in front of the participant, we delivered visual cues to orient attention to the location of target sounds and/or their temporal window. In Exp. 1 ( n = 14), we validated this visual-to-auditory cueing method in normal-hearing listeners, tested under typical binaural listening conditions. In Exp. 2 ( n = 13), we assessed the efficacy of the same visual cues in normal-hearing listeners wearing a monaural ear plug, to study the effects of simulated monaural and conductive hearing loss on visual-to-auditory attention orienting. While Exp. 1 revealed a benefit of both spatial and temporal visual cues for hearing in noise, Exp. 2 showed that only the temporal visual cues remained effective during monaural listening. These findings indicate that when the acoustic experience is altered, visual-to-auditory attention orienting is more robust for temporal compared to spatial attributes of the auditory stimuli. These findings have implications for the relation between spatial and temporal attributes of sound objects, and when planning devices to orient audiovisual attention for subjects suffering from hearing loss.