Subjects : Twelve subjects (3 Males, 9 Female) 19-28 years old

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HUMAN FREQUENCY-FOLLOWING RESPONSES TO VOICE PITCH: Relative Contributions of the Fundamental Frequency and Its HarmonicsCassie Costilow, Fuh-Cherng JengSchool of Hearing, Speech and Language Sciences, Ohio University, Athens, Ohio • Recording procedures: • Participants were seated and reclined comfortable in an acoustically sound proof booth. • Stimuli presented monaurally to the right ear via an ER-3A insert earphone with a silent interval of 50ms • EEG recorded from three surface electrodes that were placed on the scalp • Recording montage: High Forehead (non-inverting), Right Mastoid (inverting), and Left Mastoid (ground) • Impedance maintained below 3 at 10 Hz • Data Analysis: • Offline analysis completed in MatLab and SigmaPlot • Four Objective Measures: • -Frequency Error: Represents the accuracy of pitch tracking • -Slope Error: Indicates how well the brain follows the overall shape of the • pitch contour • -Tracking Accuracy: Reflects accurateness of pitch encoding in the brainstem • -Pitch Strength: Reflects robustness of the response • One-Way Repeated Measures ANOVA completed on four measures Typical Recording from Subject ENG010 Subjects: Twelve subjects (3 Males, 9 Female) 19-28 years old Hearing thresholds 20dB or under for 125, 250, 500, 1000, 2000, 4000, and 8000 Hz. Native speakers of English Stimulus: A total of 7 tokens were presented to each subject 250ms monosyllabic Mandarin syllable yi2 with a rising tone Original yi2 recording was manipulated using a high pass filter to remove frequency components to create the -f0,-h2,-h4,-h6,-h8, and +f0 tokens 2200 sweeps for each token Control condition recorded for 6 subjects in which no sound was present One-Way Repeated Measures ANOVA (statistically significant if P<0.05): The results of this study show that both the fundamental frequency and the harmonics play a large role in the processing of pitch information. A response was detected when up to the 8th harmonic was removed from the stimulus, surpassing our original hypothesis. The robust response at –h6 may indicate a sound intensity compensation occurring in the auditory system. The frequency energy in the –h6 token falls within the 1000-4000Hz range, which is the frequency range most important for speech perception. The brain may have utilized the sound energy in the token to produce a strong response that other tokens would need a greater intensity level to produce. The +f0 condition demonstrates the need for harmonics in pitch processing, as seen by the much smaller response when compared to the intact and remaining conditions. The results of this study serve to help fill in the gaps of our knowledge of how the brain processes pitch information of complex sounds. Further investigation into the contribution of the fundamental frequency and its harmonics should be completed to see if language experience has an effect on the way pitch is processed. Questions can be emailed to cc210406@ohio.edu Results Introduction Conclusions References Methods The human brain is capable of discriminating subtle changes in voice pitch from speech signals. Speech signals, like all complex sounds, consist of a fundamental frequency (f0) and component frequencies that are integer multiples of the f0, known as harmonics (Ballantyne, 1990). The phenomenon of the “missing fundamental frequency” has shown that when the f0 is removed from a complex stimulus the pitch of the f0 is still perceived (Aiken et al., 2006; Dajani et al., 2005). The ability for normal hearing adults to process changes in voice pitch has been studied with the use of the frequency following response (FFR) (Aiken et al., 2006; Dajani et al., 2005; Krishnan et al., 2004). The FFR is a scalp-recorded auditory evoked potential that follows the pitch contour of a complex stimulus. While studies have examined the phenomenon of the "missing f0“, further investigation into the contributions of the harmonics in an individual's ability to process pitch has yet to be completed. The purpose of the current study is to examine the contribution of the f0 and each harmonic in pitch processing by systematically manipulating the speech stimulus to remove component frequencies. It is hypothesized that as frequency components are removed from the stimuli, FFR recordings will show a decreasing ability to process pitch information until no response can be recorded. It is believed that a response will no longer be found after the removal of the 4th harmonic, while a slight response will still be present at the removal of the 2nd harmonic. Also, it is believed that a response will be seen when only the fundamental frequency is preserved. Aiken, S.J., & Picton, T.W. (2006). Envelope following response to natural vowels. Audiology and Neurology, 11, 213-232. Ballantyne, D. (1990). Handbook of Audiological Techniques. Rushden: Butterworth- Heinemann. 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) 1614-1518. Krishnan, A., Xu, Y., Gandour, J. T., & Cariani, P. A. (2004). Human frequency-following response: representation of pitch contours in Chinese tones. Hearing Research, 189, 1- 12. Stimulus Spectrograms