Intelligibility of speech in a virtual 3-D environment

Spatialized audio improves call sign recognition during multi-aircraft control

We investigated the impact of a spatialized audio display on response time, workload, and accuracy while monitoring auditory information for relevance. The human ability to differentiate sound direction implies that spatial audio may be used to encode information. Therefore, it is hypothesized that spatial audio cues can be applied to aid differentiation of critical versus noncritical verbal auditory information. We used a human performance model and a laboratory study involving 24 participants to examine the effect of applying a notional, automated parser to present audio in a particular ear depending on information relevance. Operator workload and performance were assessed while subjects listened for and responded to relevant audio cues associated with critical information among additional noncritical information. Encoding relevance through spatial location in a spatial audio display system--as opposed to monophonic, binaural presentation--significantly reduced response time and workload, particularly for noncritical information. Future auditory displays employing spatial cues to indicate relevance have the potential to reduce workload and improve operator performance in similar task domains. Furthermore, these displays have the potential to reduce the dependence of workload and performance on the number of audio cues.

Impact of a bone conduction communication channel on multichannel communication system effectiveness

OBJECTIVE

In this study, the impact of including a bone conduction transducer in a three-channel spatialized communication system was investigated.

BACKGROUND

Several military and security forces situations require concurrent listening to three or more radio channels. In such radio systems, spatial separation between three concurrent radio channels can be achieved by delivering separate signals to the left and right earphone independently and both earphones simultaneously. This method appears to be effective; however, the use of bone conduction as one channel may provide both operational and performance benefits.

METHOD

Three three-channel communication systems were used to collect speech intelligibility data from 18 listeners (System I, three loudspeakers; System 2, stereo headphones; System 3, stereo headphones and a bone conduction vibrator). Each channel presented signals perceived to originate from separate locations. Volunteers listened to three sets of competing sentences and identified a number, color, and object spoken in the target sentence. Each listener participated in three trials (one per system). Each trial consisted of 48 competing sentence sets.

RESULTS

Systems 2 and 3 were more intelligible than System I. Systems 2 and 3 were overall equally intelligible; however, the intelligibility of all three channels was significantly more balanced in System 3.

CONCLUSION

Replacing an air conduction transducer with a bone conduction transducer in a multichannel audio device can provide a more effective and balanced simultaneous monitoring auditory environment.

APPLICATION

These results have important design and implementation implications for spatial auditory communication equipment.

Spatial audio through a bone conduction interface

Headphones are the standard presentation device for radio communication in the military. Although bone conduction devices possess several advantages over headphones for some military applications, they are generally considered inappropriate for inclusion in a multi-channel system. The current study tested the feasibility of a multi-channel bone conduction system by measuring the localizability of spatialized auditory stimuli presented through a pair of bone conduction vibrators. Listeners localized a Gaussian noise stimulus spatialized with individualized head-related transfer functions (HRTFs). The sounds were presented from eight virtual locations on the horizontal plane (0, +/-45, +/-90, +/-135, and 180 degrees ) through either stereo headphones or a stereo bone conduction system. Localization performance was found to be nearly identical for both audio systems, indicating that bone conduction systems can be effectively used for displaying spatial information.

Simple displays of talker location improve voice identification performance in multitalker, spatialized audio environments

OBJECTIVE

The aim of this study was to assess the voice identification benefits of visual depictions of the relative locations of spatialized talkers in a serial listening task.

BACKGROUND

Although spatialized audio is known to improve speech intelligibility and voice identification accuracy within multitalker environments, prior studies have not found any additional benefit for augmenting spatialized audio with visual depictions of relative voice locations. These studies, however, were restricted to small audio environments (four voices), potentially limiting the ability of simple talker location displays to provide additional identification benefit.

METHOD

In the first experiment, 18 participants performed a voice identification task for four- and eight-voice environments under three display conditions: (a) nonspatialized voices with an audio-only display, (b) spatialized voices with an audio-only display, and (c) spatialized voices augmented by a visual display of relative talker locations. In the second experiment, 32 participants performed the same voice identification task within a spatialized eight-voice environment but with audio and visual displays of differing angular scale.

RESULTS

Visually depicting relative talker locations improved voice identification performance in terms of both accuracy and response time, particularly for more populous auditory spaces. Both auditory and visual display scale affected these benefits, with large-angle displays performing the best for both modalities.

CONCLUSION

Results indicate that simple visual representations of spatialized audio environments help listeners identify voices and that these representations are more effective when the angular spacing (auditory and visual) between talker locations is increased.

APPLICATION

These results have important implications for the design and implementation of collaborative audio environments for shared, desktop, and portable communication devices.

The effect of head-related transfer function measurement methodology on localization performance in spatial audio interfaces

OBJECTIVE

Four head-related transfer function (HRTF) data sets were compared to determine the effect of HRTF measurement methodology on the localization of spatialized auditory stimuli.

BACKGROUND

Spatial audio interfaces typically require HRTF data sets to generate the spatialized auditory stimuli. HRTF measurement is accomplished using a variety of techniques that can require several nearly arbitrary decisions about methodology. The effects of these choices upon the resulting spatial audio interface are unclear.

METHOD

Sixteen participants completed a sound localization task that included real-world, broadband stimuli spatialized at eight locations on the horizontal plane. Four different HRTF data sets were utilized to spatialize the stimuli: two publicly available HRTF data sets and two data sets obtained using different in-house measurement systems. All HRTFs were obtained from the Knowles Electronics Mannequin for Acoustics Research.

RESULTS

Unsigned localization error and proportion of front/back reversals did not differ significantly across HRTF data sets. Poorest accuracy was observed in locations near the medial (front/back) axis of the listener, mainly because of the relatively large proportions of reversals at these locations.

CONCLUSION

This study suggests that the particular generalized HRTF data set chosen for spatialization is of minimal importance to the localizability of the resulting stimuli.

APPLICATION

This result will inform the design of many spatial audio interfaces that are based upon generalized HRTFs, including wayfaring devices, communication systems, and virtual reality systems.

Spatial audio displays improve the detection of target messages in a continuous monitoring task

OBJECTIVE

The detection of target messages in a background of competing speech and the identification of the color/number combinations in those messages were examined in a continuous monitoring task.

BACKGROUND

Previous research has shown that if listeners know when and where to listen, speech-on-speech intelligibility is improved when signals are presented via a 3-D audio display as compared with a diotic display. However, the effect of display type on detection of infrequent target messages in a continuous monitoring task has not been examined.

METHOD

Participants were required to monitor five communications channels conveying messages at random intervals under each of three audio display conditions: diotic, all channels in front, and channels separated in azimuth (3-D).

RESULTS

Message detection sensitivity was significantly higher for the 3-D condition than for the in-front condition but did not differ significantly between the in-front and the diotic conditions. There were no differences in response criteria across conditions. Color/number identification sensitivity also was significantly higher for the 3-D condition than for the in-front condition but did not differ significantly between the in-front and the diotic conditions.

CONCLUSION

A 3-D audio display enhances both message detection and message identification in a continuous monitoring task.

APPLICATION

Three-dimensional audio displays would be particularly beneficial in environments such as aviation, in which the information conveyed to operators via the auditory modality can be crucial to the safe and effective performance of their work.