Effects of sex and age on auditory spatial scene analysis

Effect of early versus late onset of partial visual loss on judgments of auditory distance

SIGNIFICANCE

It is important to know whether early-onset vision loss and late-onset vision loss are associated with differences in the estimation of distances of sound sources within the environment. People with vision loss rely heavily on auditory cues for path planning, safe navigation, avoiding collisions, and activities of daily living.

PURPOSE

Loss of vision can lead to substantial changes in auditory abilities. It is unclear whether differences in sound distance estimation exist in people with early-onset partial vision loss, late-onset partial vision loss, and normal vision. We investigated distance estimates for a range of sound sources and auditory environments in groups of participants with early- or late-onset partial visual loss and sighted controls.

METHODS

Fifty-two participants heard static sounds with virtual distances ranging from 1.2 to 13.8 m within a simulated room. The room simulated either anechoic (no echoes) or reverberant environments. Stimuli were speech, music, or noise. Single sounds were presented, and participants reported the estimated distance of the sound source. Each participant took part in 480 trials.

RESULTS

Analysis of variance showed significant main effects of visual status (p<0.05) environment (reverberant vs. anechoic, p<0.05) and also of the stimulus (p<0.05). Significant differences (p<0.05) were shown in the estimation of distances of sound sources between early-onset visually impaired participants and sighted controls for closer distances for all conditions except the anechoic speech condition and at middle distances for all conditions except the reverberant speech and music conditions. Late-onset visually impaired participants and sighted controls showed similar performance (p>0.05).

CONCLUSIONS

The findings suggest that early-onset partial vision loss results in significant changes in judged auditory distance in different environments, especially for close and middle distances. Late-onset partial visual loss has less of an impact on the ability to estimate the distance of sound sources. The findings are consistent with a theoretical framework, the perceptual restructuring hypothesis, which was recently proposed to account for the effects of vision loss on audition.

An auditory brain-computer interface based on selective attention to multiple tone streams

In this study, we attempted to improve brain-computer interface (BCI) systems by means of auditory stream segregation in which alternately presented tones are perceived as sequences of various different tones (streams). A 3-class BCI using three tone sequences, which were perceived as three different tone streams, was investigated and evaluated. Each presented musical tone was generated by a software synthesizer. Eleven subjects took part in the experiment. Stimuli were presented to each user's right ear. Subjects were requested to attend to one of three streams and to count the number of target stimuli in the attended stream. In addition, 64-channel electroencephalogram (EEG) and two-channel electrooculogram (EOG) signals were recorded from participants with a sampling frequency of 1000 Hz. The measured EEG data were classified based on Riemannian geometry to detect the object of the subject's selective attention. P300 activity was elicited by the target stimuli in the segregated tone streams. In five out of eleven subjects, P300 activity was elicited only by the target stimuli included in the attended stream. In a 10-fold cross validation test, a classification accuracy over 80% for five subjects and over 75% for nine subjects was achieved. For subjects whose accuracy was lower than 75%, either the P300 was also elicited for nonattended streams or the amplitude of P300 was small. It was concluded that the number of selected BCI systems based on auditory stream segregation can be increased to three classes, and these classes can be detected by a single ear without the aid of any visual modality.

Voluntary auditory change: First-person access to agentive aspects of attention regulation

In perceptual psychology, audition and introspection have not yet received as much attention as other topics (e.g., vision) and methods (third-person paradigms). Practical examples and theoretical considerations show that it nevertheless seems promising to treat both topics in conjunction to gain insights into basic structures of attention regulation and respective agentive awareness. To this end, an empirical study on voluntary auditory change was conducted with a non-reactive first-person design. Data were analyzed with a mixed methods approach and compared with an analogous study on visual reversal. Qualitative hierarchical coding and explorative statistics yield a cross-modal replication of frequency patterns of mental activity as well as significant differences between the modalities. On this basis, the role of mental agency in perception is refined in terms of different levels of intention and discussed in the context of the philosophical mental action debate as well as of the Global Workspace/Working Memory account. As a main result, this work suggests the existence and structure of a gradual and developable agentive attention awareness on which voluntary attention regulation can build, and which justifies speaking, in a certain sense, of attentional self-perception.

Short-Term Audiovisual Spatial Training Enhances Electrophysiological Correlates of Auditory Selective Spatial Attention

Audiovisual cross-modal training has been proposed as a tool to improve human spatial hearing. Here, we investigated training-induced modulations of event-related potential (ERP) components that have been associated with processes of auditory selective spatial attention when a speaker of interest has to be localized in a multiple speaker ("cocktail-party") scenario. Forty-five healthy participants were tested, including younger (19-29 years; n = 21) and older (66-76 years; n = 24) age groups. Three conditions of short-term training (duration 15 min) were compared, requiring localization of non-speech targets under "cocktail-party" conditions with either (1) synchronous presentation of co-localized auditory-target and visual stimuli (audiovisual-congruency training) or (2) immediate visual feedback on correct or incorrect localization responses (visual-feedback training), or (3) presentation of spatially incongruent auditory-target and visual stimuli presented at random positions with synchronous onset (control condition). Prior to and after training, participants were tested in an auditory spatial attention task (15 min), requiring localization of a predefined spoken word out of three distractor words, which were presented with synchronous stimulus onset from different positions. Peaks of ERP components were analyzed with a specific focus on the N2, which is known to be a correlate of auditory selective spatial attention. N2 amplitudes were significantly larger after audiovisual-congruency training compared with the remaining training conditions for younger, but not older, participants. Also, at the time of the N2, distributed source analysis revealed an enhancement of neural activity induced by audiovisual-congruency training in dorsolateral prefrontal cortex (Brodmann area 9) for the younger group. These findings suggest that cross-modal processes induced by audiovisual-congruency training under "cocktail-party" conditions at a short time scale resulted in an enhancement of correlates of auditory selective spatial attention.

A Graphical-User-Interface-Based Azimuth-Collection Method in Autonomous Auditory Localization of Real and Virtual Sound Sources

Auditory localization of spatial sound sources is an important life skill for human beings. For the practical application-oriented measurement of auditory localization ability, the preference is a compromise among (i) data accuracy, (ii) the maneuverability of collecting directions, and (iii) the cost of hardware and software. The graphical user interface (GUI)-based sound-localization experimental platform proposed here (i) is cheap, (ii) can be operated autonomously by the listener, (iii) can store results online, and (iv) supports real or virtual sound sources. To evaluate the accuracy of this method, by using 12 loudspeakers arranged in equal azimuthal intervals of 30° in the horizontal plane, three groups of azimuthal localization experiments are conducted in the horizontal plane with subjects with normal hearing. In these experiments, the azimuths are reported using (i) an assistant, (ii) a motion tracker, or (iii) the newly designed GUI-based method. All three groups of results show that the localization errors are mostly within 5-12°, which is consistent with previous results from different localization experiments. Finally, the stimulus of virtual sound sources is integrated into the GUI-based experimental platform. The results with the virtual sources suggest that using individualized head-related transfer functions can achieve better performance in spatial sound source localization, which is consistent with previous conclusions and further validates the reliability of this experimental platform.

Transcranial direct current stimulation of posterior temporal cortex modulates electrophysiological correlates of auditory selective spatial attention in posterior parietal cortex

Speech perception in "cocktail-party" situations, in which a sound source of interest has to be extracted out of multiple irrelevant sounds, poses a remarkable challenge to the human auditory system. Studies on structural and electrophysiological correlates of auditory selective spatial attention revealed critical roles of the posterior temporal cortex and the N2 event-related potential (ERP) component in the underlying processes. Here, we explored effects of transcranial direct current stimulation (tDCS) to posterior temporal cortex on neurophysiological correlates of auditory selective spatial attention, with a specific focus on the N2. In a single-blind, sham-controlled crossover design with baseline and follow-up measurements, monopolar anodal and cathodal tDCS was applied for 16 min to the right posterior superior temporal cortex. Two age groups of human subjects, a younger (n = 20; age 18-30 yrs) and an older group (n = 19; age 66-77 yrs), completed an auditory free-field multiple-speakers localization task while ERPs were recorded. The ERP data showed an offline effect of anodal, but not cathodal, tDCS immediately after DC offset for targets contralateral, but not ipsilateral, to the hemisphere of tDCS, without differences between groups. This effect mainly consisted in a substantial increase of the N2 amplitude by 0.9 μV (SE 0.4 μV; d = 0.40) compared with sham tDCS. At the same point in time, cortical source localization revealed a reduction of activity in ipsilateral (right) posterior parietal cortex. Also, localization error was improved after anodal, but not cathodal, tDCS. Given that both the N2 and the posterior parietal cortex are involved in processes of auditory selective spatial attention, these results suggest that anodal tDCS specifically enhanced inhibitory attentional brain processes underlying the focusing onto a target sound source, possibly by improved suppression of irrelevant distracters.

Bihemispheric anodal transcranial direct-current stimulation over temporal cortex enhances auditory selective spatial attention

The capacity to selectively focus on a particular speaker of interest in a complex acoustic environment with multiple persons speaking simultaneously-a so-called "cocktail-party" situation-is of decisive importance for human verbal communication. Here, the efficacy of single-dose transcranial direct-current stimulation (tDCS) in improving this ability was tested in young healthy adults (n = 24), using a spatial task that required the localization of a target word in a simulated "cocktail-party" situation. In a sham-controlled crossover design, offline bihemispheric double-monopolar anodal tDCS was applied for 30 min at 1 mA over auditory regions of temporal lobe, and the participant's performance was assessed prior to tDCS, immediately after tDCS, and 1 h after tDCS. A significant increase in the amount of correct localizations by on average 3.7 percentage points (d = 1.04) was found after active, relative to sham, tDCS, with only insignificant reduction of the effect within 1 h after tDCS offset. Thus, the method of bihemispheric tDCS could be a promising tool for enhancement of human auditory attentional functions that are relevant for spatial orientation and communication in everyday life.

Gender effects on auditory P300: A systematic review

The evidence suggests that gender-related effects could influence the electrophysiological P300 parameters and stand as an additional source of variation for both clinical and non-clinical subjects. The aim of this paper is to characterize gender-related differences in P300 potential as elicited with simple auditory paradigms. This knowledge (1) is important for the practical assessment of P300 potential in normal and clinical populations, and (2) can provide an insight into the understanding of gender differences in pathophysiology, particularly those with differential risk or prevalence in males and females. With this review it is shown that a limited number of studies encounter possible gender effects on parameters of auditory P300, and the findings need to be read with caution due to methodological limitations of the studies. Nevertheless, evidence supports that the P300 amplitude could be significantly modulated by gender, with greater amplitude in females relative to males. Noteworthy, gender has a minimal effect on the P300 latency, and it is often comparable between males and females. Furthermore, the effect of gender on P300 could be modulated by hormonal background, anatomy and some methodological aspects.

Modulation of human auditory spatial scene analysis by transcranial direct current stimulation

Localizing and selectively attending to the source of a sound of interest in a complex auditory environment is an important capacity of the human auditory system. The underlying neural mechanisms have, however, still not been clarified in detail. This issue was addressed by using bilateral bipolar-balanced transcranial direct current stimulation (tDCS) in combination with a task demanding free-field sound localization in the presence of multiple sound sources, thus providing a realistic simulation of the so-called "cocktail-party" situation. With left-anode/right-cathode, but not with right-anode/left-cathode, montage of bilateral electrodes, tDCS over superior temporal gyrus, including planum temporale and auditory cortices, was found to improve the accuracy of target localization in left hemispace. No effects were found for tDCS over inferior parietal lobule or with off-target active stimulation over somatosensory-motor cortex that was used to control for non-specific effects. Also, the absolute error in localization remained unaffected by tDCS, thus suggesting that general response precision was not modulated by brain polarization. This finding can be explained in the framework of a model assuming that brain polarization modulated the suppression of irrelevant sound sources, thus resulting in more effective spatial separation of the target from the interfering sound in the complex auditory scene.

Competing Speech Perception in Middle Age

PURPOSE

This research forum article summarizes research from our laboratory that assessed middle-aged adults' ability to understand speech in the presence of competing talkers.

METHOD

The performance of middle-aged adults on laboratory-based speech understanding tasks was compared to that of younger and older adults.

RESULTS

Decline in the ability to understand speech in complex listening environments can be demonstrated in midlife. The specific auditory and cognitive contributors to these problems have yet to be established.

CONCLUSION

There is evidence that the ability to understand a target speech message in the presence of competing speech messages changes relatively early in the aging process. The nature and impact of these changes warrant further investigation.

Using auditory pre-information to solve the cocktail-party problem: electrophysiological evidence for age-specific differences

Speech understanding in complex and dynamic listening environments requires (a) auditory scene analysis, namely auditory object formation and segregation, and (b) allocation of the attentional focus to the talker of interest. There is evidence that pre-information is actively used to facilitate these two aspects of the so-called “cocktail-party” problem. Here, a simulated multi-talker scenario was combined with electroencephalography to study scene analysis and allocation of attention in young and middle-aged adults. Sequences of short words (combinations of brief company names and stock-price values) from four talkers at different locations were simultaneously presented, and the detection of target names and the discrimination between critical target values were assessed. Immediately prior to speech sequences, auditory pre-information was provided via cues that either prepared auditory scene analysis or attentional focusing, or non-specific pre-information was given. While performance was generally better in younger than older participants, both age groups benefited from auditory pre-information. The analysis of the cue-related event-related potentials revealed age-specific differences in the use of pre-cues: Younger adults showed a pronounced N2 component, suggesting early inhibition of concurrent speech stimuli; older adults exhibited a stronger late P3 component, suggesting increased resource allocation to process the pre-information. In sum, the results argue for an age-specific utilization of auditory pre-information to improve listening in complex dynamic auditory environments.

Impact of hearing protection devices on sound localization performance

Hearing Protection Devices (HPDs) can protect the ear against loud potentially damaging sounds while allowing lower-level sounds such as speech to be perceived. However, the impact of these devices on the ability to localize sound sources is not well known. To address this question, we propose two different methods: one behavioral and one dealing with acoustical measurements. For the behavioral method, sound localization performance was measured with, and without, HPDs on 20 listeners. Five HPDs, including both passive (non-linear attenuation) and three active (talk-through) systems were evaluated. The results showed a significant increase in localization errors, especially front-back and up-down confusions relative to the "naked ear" test condition for all of the systems tested, especially for the talk-through headphone system. For the acoustic measurement method, Head-Related Transfer Functions (HRTFs) were measured on an artificial head both without, and with the HPDs in place. The effects of the HPDs on the spectral cues for the localization of different sound sources in the horizontal plane were analyzed. Alterations of the Interaural Spectral Difference (ISD) cues were identified, which could explain the observed increase in front-back confusions caused by the talk-through headphone protectors.

Effects of anodal TDCS stimulation of left parietal cortex on visual spatial attention tasks in men and women across menstrual cycle

Sex hormonal variations have been shown to affect functional cerebral asymmetries in cognitive domains, contributing to sex-related differences in functional cerebral organization. The aim of this study was to investigate spatial attention by means of a bisection line test and computer-supported attention task during the menstrual cycle in healthy women compared to men, in basal condition and under Transcranial Direct Current Stimulation (TDCS) of the left parietal cortex. Women were studied during the menses, follicular and luteal phases, ascertained by transvaginal ultrasounds. In basal conditions, women showed a clear deviation toward the right in the bisection line test during the menstrual phase, similarly to men. The midpoint recognition in the computer-supported attention task was not influenced by the menstrual cycle for women, while men showed a significant increase in errors toward the left side. The anodal activation of the left parietal cortex did not affect the line bisection task, while in men it reduced the total amount of errors in midpoint recognition observed in the computer supported attention task. The hand-use effect demonstrated by the bisection-line test could be influenced by estrogen fluctuations, while the right hemisphere prevalence in spatial attention appears to be gender-related and scarcely influenced by the menstrual cycle. The left parietal cortex seems to exert a scarce effect on hand-use effect, while its activation is able to revert sex related right hemisphere supremacy.

The effect of brain lesions on sound localization in complex acoustic environments

Localizing sound sources of interest in cluttered acoustic environments--as in the 'cocktail-party' situation--is one of the most demanding challenges to the human auditory system in everyday life. In this study, stroke patients' ability to localize acoustic targets in a single-source and in a multi-source setup in the free sound field were directly compared. Subsequent voxel-based lesion-behaviour mapping analyses were computed to uncover the brain areas associated with a deficit in localization in the presence of multiple distracter sound sources rather than localization of individually presented sound sources. Analyses revealed a fundamental role of the right planum temporale in this task. The results from the left hemisphere were less straightforward, but suggested an involvement of inferior frontal and pre- and postcentral areas. These areas appear to be particularly involved in the spectrotemporal analyses crucial for effective segregation of multiple sound streams from various locations, beyond the currently known network for localization of isolated sound sources in otherwise silent surroundings.