Enhancement of temporal periodicity cues in cochlear implants: Effects on prosodic perception and vowel identification

Abstract

Standard continuous interleaved sampling processing, and a modified processing strategy designed to enhance temporal cues to voice pitch, were compared on tests of intonation perception, and vowel perception, both in implant users and in acoustic simulations. In standard processing, 400 Hz low-pass envelopes modulated either pulse trains (implant users) or noise carriers (simulations). In the modified strategy, slow-rate envelope modulations, which convey dynamic spectral variation crucial for speech understanding, were extracted by low-pass filtering (32 Hz). In addition, during voiced speech, higher-rate temporal modulation in each channel was provided by 100% amplitude-modulation by a sawtooth-like wave form whose periodicity followed the fundamental frequency (F0) of the input. Channel levels were determined by the product of the lower- and higher-rate modulation components. Both in acoustic simulations and in implant users, the ability to use intonation information to identify sentences as question or statement was significantly better with modified processing. However, while there was no difference in vowel recognition in the acoustic simulation, implant users performed worse with modified processing both in vowel recognition and in formant frequency discrimination. It appears that, while enhancing pitch perception, modified processing harmed the transmission of spectral information.

Spectral and temporal cues for speech recognition: Implications for auditory prostheses

“…Xu et al (2002) also found that, as in English phoneme recognition, there was a tradeoff between the temporal and spectral cues for lexical tone recognition. Efforts aimed at enhancing the temporal envelope cues for tone recognition or pitch perception using acoustic simulations or actual cochlear implants have yielded only modest success (e.g., Geurts and Wouters, 2001;Green et al, 2004Green et al, , 2005Hamilton et al, 2007;Laneau et al, 2006;Luo and Fu, 2004;Vandali et al, 2005Vandali et al, , 2007. On the other hand, few studies have attempted to manipulate the spectral cues to improve tone recognition or pitch perception (e.g., Geurts and Wouters, 2004).…”

Cochlear implants: A remarkable past and a brilliant future

“…Thus, less-thanresolute representations of F0s is a problem for implants, and this problem has received considerable attention (e.g., Wouters, 2001, 2004;Luo and Fu, 2004;Green et al, 2005;Laneau et al, 2006;Carroll and Zeng, 2007;Chatterjee and Peng, 2007;Sucher and McDermott, 2007). Unfortunately, a way to improve the representations has not been identified to date despite these efforts.…”

Effects of envelope bandwidth on the intelligibility of sine- and noise-vocoded speech

“…Sentences were drawn from 30 sentences previously used by Green et al ͑2005͒. These consisted of simple declarative sentences that could be produced as either a statement or question; for example, "They're playing in the garden."…”