Complex Auditory Environments Research Articles

Some brain mechanisms for auditory scene analysis.

Detection and discrimination of sounds in complex auditory environments is facilitated by knowledge of the locations of sound sources and by spatial separation of signals and maskers. In studies of the spatial sensitivity of auditory cortical neurons in anesthetized cats, we find that location‐dependent variation in temporal spike patterns can signal sound‐source locations throughout up to 360 deg of space. In awake cats, spatial receptive fields can be similarly broad, although cortical neurons show a greater diversity of temporal patterns than is seen in anesthetized conditions. Our recent results demonstrate that spatial tuning tends to sharpen when a cat is engaged in an auditory task, compared to idle conditions, and that tuning can sharpen even further when the task involves sound localization. In human psychophysical studies, spatial hearing permits perceptual “stream segregation” of multiple temporally interleaved sequences of sounds. In parallel studies of the auditory cortex in anesthetized cats...

Attention to human speakers in a virtual auditory environment: Brain potential evidence

Listening to a speech message requires the accurate selection of the relevant auditory input especially when distracting background noise or other speech messages are present. To investigate such auditory selection processes we presented three different speech messages simultaneously spoken by different actors at separate spatial locations (− 70, 0, 70/ azimuth). Stimuli were recorded using an artificial head with microphones embedded in the “auditory canals” to capture the interaural time and level differences as well as some of the filter properties of the outer ear structures as auditory spatial cues, thus creating a realistic virtual auditory space. In a given experimental run young healthy participants listened via headphones and either attended to the rightmost or the leftmost message in order to comprehend the story. Superimposed on the speech messages task irrelevant probe stimuli (syllables sharing spatial and spectral characteristics, 4 probes/s) were presented that were used for the generation of event-related brain potentials computed from 29 channels of EEG. ERPs to probe stimuli were characterized by a negativity starting at 250 ms with a contralateral frontal maximum for the probes sharing spatial/spectral features of the attended story relative to those for the unattended message. The relatively late onset of this attention effect was interpreted to reflect the task demands in this complex auditory environment. This study demonstrates the feasibility to use virtual auditory environments in conjunction with the probe technique to study auditory selection under realistic conditions.

Comparison of pre‐ and post‐cueing in a multiple‐source sound localization task

Although most sound localization research has examined the ability of listeners to determine the location of a single sound presented in a quiet (typically anechoic) environment, most real‐world listening situations are more complex, with multiple simultaneous sounds. Here, an initial experiment, designed to examine localization in multisource environments, is described. Listeners judged the location of a target signal (speech or environmental sound, presented normally or time‐reversed) masked by up to four simultaneous sounds. In each block of trials, the observation interval was either preceded by, or followed by, a cueing interval, during which the stimulus to be localized was identified. It was expected that these two approaches would lead to different answers, as the associated tasks presumably address different listening strategies (i.e., analytic listening versus monitoring). The results indicate that, in all conditions, localization errors increase as the number of simultaneous sources increases. Moreover, performance degrades more rapidly in the post‐cue condition than in the pre‐cue condition. Surprisingly, this difference occurs for as few as two simultaneous sources, suggesting that there is a substantial cost when listeners are asked to remember what sounds were present and where those sounds were located in a complex auditory environment. [Work supported by AFOSR.]

The role of predictive models in the formation of auditory streams

Sounds provide us with useful information about our environment which complements that provided by other senses, but also poses specific processing problems. How does the auditory system distentangle sounds from different sound sources? And what is it that allows intermittent sound events from the same source to be associated with each other? Here we review findings from a wide range of studies using the auditory streaming paradigm in order to formulate a unified account of the processes underlying auditory perceptual organization. We present new computational modelling results which replicate responses in primary auditory cortex [Fishman, Y.I., Arezzo, J.C., Steinschneider, M., 2004. Auditory stream segregation in monkey auditory cortex: effects of frequency separation, presentation rate, and tone duration. J. Acoust. Soc. Am. 116, 1656–1670; Fishman, Y. I., Reser, D. H., Arezzo, J.C., Steinschneider, M., 2001. Neural correlates of auditory stream segregation in primary auditory cortex of the awake monkey. Hear. Res. 151, 167–187] to tone sequences. We also present the results of a perceptual experiment which confirm the bi-stable nature of auditory streaming, and the proposal that the gradual build-up of streaming may be an artefact of averaging across many subjects [Pressnitzer, D., Hupé, J. M., 2006. Temporal dynamics of auditory and visual bi-stability reveal common principles of perceptual organization. Curr. Biol. 16(13), 1351–1357.]. Finally we argue that in order to account for all of the experimental findings, computational models of auditory stream segregation require four basic processing elements; segregation, predictive modelling, competition and adaptation, and that it is the formation of effective predictive models which allows the system to keep track of different sound sources in a complex auditory environment.

Auditory gating in schizophrenia: a pilot study of the precedence effect

Individuals with schizophrenia are known to exhibit diminished auditory gating, as manifested by prepulse inhibition of the startle response and suppression of the P50 evoked potential. Those observations indicate that schizophrenics have deficits of inhibitory auditory processing. The precedence effect is a phenomenon in which inhibitory processing in the auditory system aids the localization of sound sources and segregation of speech in complex auditory environments. We tested the hypothesis that schizophrenic subjects would exhibit deficits in psychophysical tests of the precedence effect. The performance of 12 male medicated schizophrenic subjects was compared with that of 12 male comparison subjects. Schizophrenics and comparison subjects clearly demonstrated all three aspects of the precedence effect that were evaluated: echo suppression, buildup of echo suppression, and breakdown of echo suppression. In none of these aspects did the performance of schizophrenic subjects differ significantly from that of the comparison subjects. These findings suggest that abnormalities of auditory spatial processing and speech segregation are unlikely to contribute to the clinical pathology of schizophrenia.

Perceptual audio rendering of complex virtual environments

We propose a real-time 3D audio rendering pipeline for complex virtual scenes containing hundreds of moving sound sources. The approach, based on auditory culling and spatial level-of-detail, can handle more than ten times the number of sources commonly available on consumer 3D audio hardware, with minimal decrease in audio quality. The method performs well for both indoor and outdoor environments. It leverages the limited capabilities of audio hardware for many applications, including interactive architectural acoustics simulations and automatic 3D voice management for video games.Our approach dynamically eliminates inaudible sources and groups the remaining audible sources into a budget number of clusters. Each cluster is represented by one impostor sound source, positioned using perceptual criteria. Spatial audio processing is then performed only on the impostor sound sources rather than on every original source thus greatly reducing the computational cost.A pilot validation study shows that degradation in audio quality, as well as localization impairment, are limited and do not seem to vary significantly with the cluster budget. We conclude that our real-time perceptual audio rendering pipeline can generate spatialized audio for complex auditory environments without introducing disturbing changes in the resulting perceived soundfield.

Neural basis of hearing in real-world situations.

In real-world situations animals are exposed to multiple sound sources originating from different locations. Most vertebrates have little difficulty in attending to selected sounds in the presence of distractors, even though sounds may overlap in time and frequency. This chapter selectively reviews behavioral and physiological data relevant to hearing in complex auditory environments. Behavioral data suggest that animals use spatial hearing and integrate information in spectral and temporal domains to determine sound source identity. Additionally, attentional mechanisms help improve hearing performance when distractors are present. On the physiological side, although little is known of where and how auditory objects are created in the brain, studies show that neurons extract behaviorally important features in parallel hierarchically arranged pathways. At the highest levels in the pathway these features are often represented in the form of neural maps. Further, it is now recognized that descending auditory pathways can modulate information processing in the ascending pathway, leading to improvements in signal detectability and response selectivity, perhaps even mediating attention. These issues and their relevance to hearing in real-world conditions are discussed with respect to several model systems for which both behavioral and physiological data are available.