Intelligibility and Localization of Speech from Virtual Directions

Abstract

We studied the intelligibility of speech and the ability of listeners to localize speech when synthetic direction information was added to the signal. Masked thresholds for single synthesized words were measured for simulated, horizontal angular separations of speech in the presence of a masking noise. Speech recognition was measured using the Modified Rhyme Test; the masker was broad-band white noise. A single set of head-related transfer functions conditioned the speech and noise waveforms presented over headphones, and listeners were free to move their heads relative to the apparent directions of these signals. The masker was fixed at 0 deg, and when speech was presented from other azimuths, its intelligibility typically increased by 4 to 5 dB. Individuals' masked thresholds were variable yet repeatable, and the plot of threshold by azimuth seemed unique to each subject. In a separate test, the same listeners were asked to estimate the azimuth of items from the rhyme test. Localization was accurate and performance was similar to previous work, except that confusions of source locations in the front and rear hemispheres were evenly distributed across azimuth.

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References

Begault, D. R. , and Wenzel, E. M. (1991) Headphone localization of speech stimuli. In Proceedings of the Human Factors Society 35th Annual Meeting (pp. 82–86). Santa Monica, CA: Human Factors and Ergonomics Society.

Bronkhorst, A. W. , and Plomp, R. (1988). The effect of head-induced interaural time and level differences on speech intelligibility in noise. Journal of the Acoustical Society of America, 83, 1508–1516.

Dirks, D. D. , and Wilson, R. H. (1969). The effect of spatially separated sound sources on speech intelligibility. Journal of Speech and Hearing Research, 12, 5–38.

Makous, J. C. , and Middlebrooks, J. C. (1990). Twodimensional sound localization by human listeners. Journal of the Acoustical Society of America, 87, 2188–2200.

Oldfield, S. R. , and Parker, S. P. A. (1984). Sound localisation: a topography of auditory space. 1. Normal hearing conditions. Perception, 13, 581–600.

Perrott, D. R. , Saberi, K. , Brown, K. , and Strybel, T. Z. (1990). Auditory psychomotor coordination and visual search behavior. Perception and Psychophysics, 48, 214–226.

Perrott, D. R. , Sadralodabai, T. , Saberi, K. , and Strybel, T. Z. (1991). Aurally aided visual search in the central visual field: Effects of visual load and visual enhancement of the target. Human Factors, 33, 389–400.

Sorkin, R. D. , Wightman, F. L. , Kistler, D. S. , and Elvers, G. C. (1989). An exploratory study of the use of movement-correlated cues in an auditory head-up display. Human Factors, 31, 161–166.

Tonning, F. M. (1971). Directional audiometry: II. The influence of azimuth on the perception of speech. Acta Otolaryngologica, 72, 352–357.

10.

Wenzel, E. M. (1992). Localization in virtual acoustic displays. Presence: Teleoperators and Virtual Environments, 1, 80–107.

11.

Wenzel, E. M. , Wightman, F. L. , and Kistler, D. J. (1991). Localization with non-individualized virtual display cues. In Proceedings of CHI'91, ACM Conference on Computer-Human Interaction (pp. 351–395). New York: Association for Computing Machinery.

12.

Wightman, F. L. , and Kistler, D. J. (1989). Headphone simulation of free-field listening: II. Psychophysical validation. Journal of the Acoustical Society of America, 85, 868–878.