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Re: Phoneme categorization in noise

Another way to increase difficulty is to use a vocoder. There are multiple options for vocoding, but the basic idea is to replace portions of the spectrum with carriers comprised of sinewaves or noise bands, resulting in the loss of spectral resolution. Those carriers can either be matched (in center frequency) to the spectral regions that they represent, or they can be shifted in frequency (as is the case in some cochlear implant simulations), or they can be compressed in frequency range. All of these changes result in speech that is difficult (but not impossible) to perceive.Â
A common "classic" citation for noise band vocoding is Shannon et al. (1995). Another more recent one with more details about the number of spectral and temporal bands is by Xu et al. (2005). Another one I like that incorporates frequency compression isÂBaÅkent and Shannon (2003). There are many more papers that address these techniques, but these are straightforward and easy to understand. Here are the references:

BaÅkent, D., & Shannon, R. (2003). Speech recognition under conditions of frequency-place compression and expansion.ÂJournal of the Acoustical Society of America, 113, 2064â2076.

Shannon, R., Zeng, F-G., Kamath, V., Wygonski, J., & Ekelid, M. (1995). Speech recognition with primarily temporal cues.âÂÂScience,Â270, 303â304.

Xu, L., Thompson, K. & Pfingst, B. (2005). Relative contributions of spectral and temporal cues for phoneme recognition.ÂJournal of the Acoustical Society of America, 117,Â3255-3267.

On Wed, Feb 15, 2012 at 7:00 AM, Daniela Sammler <sammler@xxxxxxxxxx> wrote:
Dear list,

I need to increase the difficulty of a phoneme categorization task (e.g. "ba" vs "pa"). One possibility would be to present the phonemes in noise to receive a shallower psychometric function.

Is this the way to go or is there any other/better way to increase difficulty in phoneme categorization?

Thank you very much!
Kind regards,

Daniela SAMMLER, Ph.D.
Max Planck Institute for
Human Cognitive and Brain Sciences
Stephanstr. 1a
04103 Leipzig
phone: +49 341 9940 2679
fax: Â +49 341 9940 2260