INTRODUCTION

1. intact -f0 -h2 -h4 -h6 -h8 +f0 intact -f0 -h2 -h4 -h6 -h8 +f0 Human frequency-following responses to voice pitch: Relative contributions of the fundamental frequency and its harmonics Daniela Stangherlin, Fuh-Cherng Jeng Ohio University, Athens, OH INTRODUCTION METHOD RESULTS The human voice carries pitch information that can be coded by the auditory system, aiding in language development and the perception of speech. In normal-hearing adults, changes in voice pitch have been identified via the frequency-following response (FFR) (Krishnan et al., 2004). FFR responses obtained using stimuli with various amounts of harmonic energy removed may provide further insight into the stimulus parameters reflected within such recordings and the mechanism(s) underlying the generation of this electrophysiologic measure. Recent studies have demonstrated that FFR spectrograms for normal-hearing adults contain energy bands at several harmonics (Krishnan et al., 2004). When f0 is removed from the stimulus, voice pitch can still be perceived as the remaining harmonics in the acoustic signal are able to provide sufficient pitch cues (Dajani et al., 2005). A rising pitch (yi2) speech token produces the most robust FFR recordings (Krishnan et al., 2004; Krishnan et al., 2008). These results indicate that frequency cues, such as those commonly found in tonal languages (e.g. Mandarin Chinese), can serve as a means by which to investigate the relationship between FFR and pitch perception. Purpose The specific aim of this study was to determine the relative contribution of the presence or absence of acoustic energy at f0 and its harmonics as evidenced by the strength of the pitch contours within FFR recordings. Hypothesis It was hypothesized that adult native speakers of Chinese would be able to process voice pitch effectively even when f0 is removed from the acoustic signal. In addition, it was anticipated that pitch processing will diminish with the removal of the 2nd through 8th harmonics from the acoustic signal. • Participants • 12 adult native speakers of Mandarin Chinese aged 18 • to 30 years (6 male, 6 female; mean age: 25 years) with • normal hearing status • Stimuli • FFRs were elicited using a monosyllabic 250ms rising pitch • Chinese lexical tone “yi” /i/ • The speech stimulus was recorded by a native Mandarin • Chinese male speaker and degraded by removing • harmonics to create seven tokens • Recording • A one-channel recording montage was used by placing • gold-plated recording electrodes on the high forehead (Fz) • and left and right mastoids (M1, M2) • Experimental Protocol • Monaural presentation via an ER-3A insert earphone • 2000 repetitions with an inter-stimulus interval of 45ms • Tokens were presented at 70 dB SPL • Analysis • Responses were evaluated using four indexes: • Frequency error – represents the accuracy of pitch tracking • Slope error – indicates how well the shape of the f0 contour is preserved • Tracking accuracy – is a reflection of the authenticity of pitch encoding in the brainstem • Pitch strength – reflects the robustness of neural phase-locking Stimulus Spectrograms Recording Spectrograms Objective Indexes CONCLUSION REFERENCES • Adult native speakers of Chinese are able to process voice pitch even when f0 is removed from the acoustic signal • Pitch processing diminishes as more harmonics are removed from the acoustic signal as evidenced by pitch strength • Beyond removal of the 4th harmonic, the remaining harmonics are unable to provide sufficient pitch cues • Dajani, H. R., Purcell, D., Wong, W., Kunov, & H., Picton, T.W. (2005). • Recording human evoked potentials that follow the pitch contour of a natural vowel. IEEE Transactions on Biomedical Engineering, 52(9), 1614-1618. • Krishnan, A., Swaminathan, J., & Gandour, J. T. (2008). Experience-dependent • enhancement of linguistic pitch representation in the brainstem is not specific to a speech context. Journal of Cognitive Neuroscience, 21(6), 1092-1105. • Krishnan, A., Xu, Y., Gandour, J., & Cariani, P. (2004). Human frequency- • following response: representation of pitch contours in Chinese tones. Hearing Research, 189, 1-12. • ds502007@ohio.edu