Joshua M. Alexander
Research Interests / Training Areas:
- Speech Perception
- Auditory Perception
Joshua M. Alexander received his Ph.D. in Audiology (psychoacoustics) and post-doctoral training in speech perception at the University of Wisconsin- Madison. Before coming to Purdue, he completed both clinical and post-doctoral fellowships at Boys Town National Research Hospital in Omaha, Nebraska.
Research interests focus on auditory processes contributing to speech perception deficits in hearing-impaired listeners and signal processing techniques to overcome them. Ongoing projects include work on frequency-lowering techniques, wide dynamic range compression, and speech enhancement techniques. Dr. Alexander has two patents pending on techniques for frequency-lowering and speech enhancement. Discovery is aided by an innovative approach by which these signal processing techniques and realistic hearing aid amplification are simulated in the laboratory on a PC. This allows the researchers in the lab to know precisely the effect that their manipulations have on the acoustic signal as they try to relate listener performance back to psychophysical estimates of cochlear filtering, auditory nerve models, and cognitive processing.
The framework guiding the discovery process involves the interplay of three key components: basic research (speech perception and psychoacoustic deficits); applied research (digital signal processing algorithms intended for hearing aids and automatic speech recognition); and modeling. Ongoing efforts encompass two main lines of research: understanding existing technology and developing new technology. Recently, effort has been directed towards developing an auditory nerve model (neural-scaled entropy model) that quantifies information in a speech signal. The intent is to help explain the effects that different signal processing strategies have on speech perception as a function of hearing loss. The immediate goal is to explain differences in outcomes that have been observed in the lab associated with different frequency-lowering ('information re-coding') techniques so that better solutions can be devised.
Alexander, J. M. and Masterson, K. M. (accepted with revision). “Effects of WDRC release time and number of channels on output SNR and speech recognition,” Ear and Hearing.
Alexander, J. M., Kopun, J.G., and Stelmachowicz, P. G. (accepted with revision). “Effects of frequency compression and frequency transposition on fricative and affricate perception in listeners with normal hearing and mild to moderate hearing loss,” Ear and Hearing.
McCreery, R. W., Alexander, J. M., Brennan, M. A., Hoover, B., Kopun, J., and Stelmachowicz, P. G. (in press). “The influence of audio-visual exposure on speech recognition with nonlinear frequency compression for children and adults with hearing loss,” Ear and Hearing.
Alexander, J. M. (2013). “Individual variability in recognition of frequency-lowered speech,” Semin Hear, 34, 86-109.
Alexander, J. M., and Hariram, V. (2013). “Neural-scaled entropy as a Model of Information for Speech Perception,” Proc Meet Acoust, 19, 050179, doi: 10.1121/1.4799891.Alexander, J. M., Jenison, R. L., and Kluender, K. R. (2011). “Real-time contrast enhancement to improve speech recognition,” PLoS ONE 6(9), e24630, doi:10.1371/journal.pone.0024630.