Dr. Zahorik's lab currently studies several aspects of spatial hearing:

Directional Localization
Auditory space is not directly encoded by the ear. Spatial aspects of sound must instead be inferred from various acoustical properties of the sounds reaching the ears. In the case of sound direction, two primary types of acoustic properties, or cues, are thought to determine the perceived direction of sound: binaural cues (two ears) and monaural cues (one ear). Binaural cues include the directionally dependent differences in sound arrival time at the two ears (interaural time differences) and the directionally dependent differences in sound level at the two ears (interaural level differences). Humans can use these two binaural cues to effectively encode the lateral positions of sound sources. Monaural cues relate to the directionally dependent filtering caused by sound propagation around the external ear and head, and are thought to be important for encoding sound source position in the vertical and front/back dimensions. Areas of current research interest include: Localization errors in the front/back dimension; virtual sound source methods for quantifying and controlling the acoustic cues to sound direction; localization of multiple sound sources; individual differences in the acoustic cues to source direction; monaural sound localization.

Recent Publications:

Zahorik, P., Bangayan, P., Sundareswaran, V., Wang, K, & Tam, C. (2006, in press). Perceptual recalibration in human sound localization: Learning to remediate front-back reversals. Journal of the Acoustical Society of America.

Wightman, F. L., & Kistler, D. J. (2005). Measurement and validation of human HRTFs for use in hearing research. Acta Acustica, 91, 429-439.

Langendijk, E. H., Kistler, D. J., & Wightman, F. L. (2001). Sound localization in the presence of one or two distracters. Journal of the Acoustical Society of America, 109(5 Pt 1), 2123-2134.

Wightman, F. L., & Kistler, D. J. (1999). Resolution of front-back ambiguity in spatial hearing by listener and source movement. Journal of the Acoustical Society of America, 105(5), 2841-2853.

Distance Localization
Like direction, sound source distance must also be inferred from various acoustical properties of the sounds reaching the ears. Distance dependent acoustical parameters include: sound intensity, the ratio of direct-to-reverberant sound energy, spectral shape, and binaural differences. Because many of these acoustical distance cues can be affected by factors other than source distance, distance information is likely combined from multiple cues. Even under ideal conditions, however, this cue combination process results in relatively inaccurate distance estimation performance when compared to directional localization.

Recent Publications:

Zahorik, P., Brungart, D. S., & Bronkhorst, A. W. (2005). Auditory distance perception in humans: A summary of past and present research. Acta Acustica, 91(3), 409-420.

Zahorik, P. (2002). Assessing auditory distance perception using virtual acoustics. Journal of the Acoustical Society of America, 111(4), 1832-1846.

Zahorik, P. & Wightman, F. L. (2001). Loudness constancy with varying sound source distance. Nature Neuroscience, 4(1), 78-83.

Hearing in Reverberant Environments
The processes by which we hear auditory events in most everyday acoustic environments that produce indirect sound (e.g. echoes, reflections, reverberation) are complex and not well understood. Under certain circumstances, indirect sound can facilitate speech communication and certain aspects of sound localization. In other circumstances, however, indirect sound can produce deficits in these and other abilities that can be particularly large for individuals with hearing impairment. Recent results have demonstrated that some aspects of indirect sound processing appear to be affected by previous exposure to the acoustic environment, which suggests a form of perceptual adaptation. Although these adaptation effects can be substantial for situations with a single echo, the effects have not been evaluated in more realistic acoustic environments with complex patterns of indirect sound resulting from multiple echoes and reverberation. This project seeks an understanding of the mechanisms and the potentially adaptive processes that subserve auditory localization and communication in everyday acoustic environments with complex patterns of indirect sound and the potential impact of hearing loss on these processes.

Recent Publications:

Zahorik, P. (2005). Measuring precedence effect buildup using subjective scaling methods. Association for Research in Otolaryngology Abstracts, 28, 338.

Zahorik, P. (2004). Perceptual scaling of room reverberation. Journal of the Acoustical Society of America, 115(5), 2598.

Zahorik, P. (2002). Direct-to-reverberant energy ratio sensitivity. Journal of the Acoustical Society of America, 112(5), 2110-2117.

Volunteer Opportunities:
All of the research programs conducted in Dr. Zahorik's laboratory depend on volunteer participants to serve as "listeners". These individuals are recruited from the UofL student population, the adjacent Louisville Deaf Oral School, and the surrounding community. All projects involving volunteer participants follow informed consent procedures approved by the UofL Human Subjects Protection Program (IRB). For more information on which projects need volunteer listeners, contact Dr. Zahorik at Pavel.Zahorik@louisville.edu  or 502-852-3861.

Staff:
Dr. Pavel Zahorik, Ph. D.
Eugene Brandewie, Graduate Assistant
Devan Haulk, Undergraduate Assistant

For more information regarding The Heuser Hearing Institute email us at info@thehearinginstitute.org