RESULTS

1. Effects of Sweep Rate on the Frequency-Following Response Cassie Costilow, Fuh-CherngJeng School of Rehabilitation and Communication Sciences, Ohio University, Athens, Ohio, USA INTRODUCTION RESULTS CONCLUSIONS and DISCUSSION Universal Newborn Hearing Screening programs have helped to identify infants with hearing loss before they leave the hospital. While we have screening tools to detect hearing loss at birth, no screener exists to identify deficits in pitch processing. A screening tool to identify individuals with such deficits could utilize the frequency-following response (FFR). Described by Worden and Marsh in 1968, the FFR is a scalp-recorded auditory evoked potential that follows the pitch contour of the auditory signal, reflecting neural phase-locked activity. The objective and non-invasive nature of the FFR make it an ideal method for investigating the brain’s pitch processing mechanism. As reported by Jeng and colleagues (2011), early maturation of voice-pitch processing occurs as early as the first three days of life. This study found comparable FFRs to a monosyllable, /i/, with a rising pitch in Chinese infants, American infants, and American adults, suggesting a biological basis for pitch encoding at the brainstem level. Recent studies have demonstrated deficits in pitch encoding at the brainstem level in children with language-based learning problems (Wible, Nicol, & Kraus, 2004), some children on the autism spectrum (Russo et. al., 2008), and children with specific language impairment (SLI) (Basu, Krishnan, & Weber-Fox, 2010) when compared to their typically developing peers. Basu et al. (2010) examined FFRs in typically developing children and children with SLI to up-swept and down-swept tones that increased in sweep rate. While both typically developing and SLI children were able to process the lower sweep rates, SLI children exhibited poor FFRs at the two highest sweep rates (5333 and 6667 Hz/sec, respectively). This study provide some evidence that there may be limitations to the brainstem’s ability to process stimuli with rapid changes in sweep rate. However, a more through study is warranted to determine if there is indeed a limit to this ability. The aim of the current study was to determine the limits of the brainstem’s pitch encoding mechanism for varying degrees of rising and falling sweep rates, as well as the effects of the listener’s linguistic background on this response. It was hypothesized that (1) the FFR would diminish with increasing sweep rate, until a response could no longer be recorded, (2) a response would only be recordable for conditions with an absolute slope of 10 kHz/sec or less, and (3) Chinese and American participants would exhibit similar limitations of pitch encoding, although Chinese responses would be more robust. • This study demonstrated: • This study examined the effects of rising and falling sweep rates on the FFR to tonal sweeps. • The FRR was recordable for all stimulus conditions, including the highest sweep rates (50000 Hz/sec and -50000 Hz/sec). • Stronger FFRs were recorded at sweep rates below ±10000 Hz/sec • There were no significant differences revealed in pitch-tracking ability between FFRs of American and Chineseparticipants (Figure 2). • Further investigation into the effects of sweep rate on the FFR are needed for application in a screening tool. p = 0.75 A B p = 0.22 REFERENCES • Basu, M., Krishnan, R., Weber-Fox, C. (2010). Degraded brainstem representations of tonal sweeps in children with specific language impairment. Developmental Science, 13, 77-91. • Jeng, FC., Hu, J., Dickman, B., Montgomery-Reagan, K., Tong, M., Wu, G., Lin, CD. (2011). Cross-linguistic comparison of frequency-following responses to voice pitch in American and Chinese neonates and adults. Ear and Hearing, 32(6), 699-707. • Russo, N.M. et al. (2008). Deficit brainstem encoding of pitch in children with Autism Spectrum Disorders. Clinical Neurophysiology, 119, 1720-1731. • Wible, B., Nicol, T., Kraus, N. (2004). Atypical brainstem representation of onset and formant structure of speech sounds in children with language-based learning problems. Biological Psychology, 67, 299-317. • Worden, F.G., Marsh, J.T. (1968). Frequency following (microphonic-like) neural responses evoked by sound. Electroencephalography and Clinical Neurophysiology, 25, 42-52. METHODS • PARTICIPANTS • Twelve native speakers of American English • -(8 females, mean age = 23.7 yr., SD = .97) • Twelve native speakers of Mandarin Chinese • -(6 females, mean age = 25 yr., SD = 3.64) • Normal hearing • -Thresholds ≤ 20 dB HL for octave frequencies between 250 and 8000 Hz • 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 45ms • EEG recorded from three surface electrodes that were placed on the scalp • Impedance maintained below 3 kΩ at 10 Hz • Recording montage: Fpz (non-inverting), M2 (inverting), and Low forehead (ground) • DATA ANALYSIS • Offline analysis completed in MatLab and SigmaPlot • Two Objective Measures: • -Frequency Error: Represents the accuracy of pitch tracking • -Spectral Amplitude: Reflects robustness of the response • A two-way repeated measures ANOVA was conducted to determine significance across the listeners’ linguistic background and the seven experimental conditions. A p value of <0.05 was considered statistically significant. • STIMULUS • Twelve 100ms tokens consisting of tonal sweeps with a rising or falling pitch trajectory • 2000 sweeps C Fig. 1 (Top left) Spectrograms of stimuli. Fig. 2 (Above) Group comparisons plotted to quantify pitch-tracking accuracy between Americanand ChineseFFRs using two objective indices: Frequency Error (top), p = 0.047; and Spectral Amplitude (bottom), p = 0.375. No significant difference between groups for either objective measure. CONTACT INFORMATION D • Cassie Costilow • School of Rehabilitation and Communication Sciences • Ohio University • Athens, OH 45701 • E-mail: cc210406@ohio.edu Fig. 3 (Left) Grand-averaged spectrograms and time waveforms of the FFR to rising and falling tonal sweeps recorded from 12 American participants(A and B) and 12 Chinese participants(C and D) for all of the testing conditions.