Publications by authors named "Ananthanarayan Krishnan"

59 Publications

Frequency-Following Response to Steady-State Vowel in Quiet and Background Noise Among Marching Band Participants With Normal Hearing.

Am J Audiol 2022 Aug 9:1-18. Epub 2022 Aug 9.

Department of Speech, Language, and Hearing Sciences, Purdue University, West Lafayette, IN.

Objective: Human studies enrolling individuals at high risk for cochlear synaptopathy (CS) have reported difficulties in speech perception in adverse listening conditions. The aim of this study is to determine if these individuals show a degradation in the neural encoding of speech in quiet and in the presence of background noise as reflected in neural phase-locking to both envelope periodicity and temporal fine structure (TFS). To our knowledge, there are no published reports that have specifically examined the neural encoding of both envelope periodicity and TFS of speech stimuli (in quiet and in adverse listening conditions) among a sample with loud-sound exposure history who are at risk for CS.

Method: Using scalp-recorded frequency-following response (FFR), the authors evaluated the neural encoding of envelope periodicity (FFR) and TFS (FFR) for a steady-state vowel (English back vowel /u/) in quiet and in the presence of speech-shaped noise presented at +5- and 0 dB SNR. Participants were young individuals with normal hearing who participated in the marching band for at least 5 years (high-risk group) and non-marching band group with low-noise exposure history (low-risk group).

Results: The results showed no group differences in the neural encoding of either the FFR or the first formant (F1) in the FFR in quiet and in noise. Paradoxically, the high-risk group demonstrated enhanced representation of F2 harmonics across all stimulus conditions.

Conclusions: These results appear to be in line with a music experience-dependent enhancement of F2 harmonics. However, due to sound overexposure in the high-risk group, the role of homeostatic central compensation cannot be ruled out. A larger scale data set with different noise exposure background, longitudinal measurements with an array of behavioral and electrophysiological tests is needed to disentangle the nature of the complex interaction between the effects of central compensatory gain and experience-dependent enhancement.
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http://dx.doi.org/10.1044/2022_AJA-21-00226DOI Listing
August 2022

Cortical hemisphere preference and brainstem ear asymmetry reflect experience-dependent functional modulation of pitch.

Brain Lang 2021 10 22;221:104995. Epub 2021 Jul 22.

Department of Speech Language Hearing Sciences, Purdue University, Lyles Porter Hall, 715 Clinic Drive, West Lafayette, IN 47907, USA. Electronic address:

Temporal attributes of pitch processing at cortical and subcortical levels are differentially weighted and well-coordinated. The question is whether language experience induces functional modulation of hemispheric preference complemented by brainstem ear symmetry for pitch processing. Brainstem frequency-following and cortical pitch responses were recorded concurrently from Mandarin and English participants. A Mandarin syllable with a rising pitch contour was presented to both ears with monaural stimulation. At the cortical level, left ear stimulation in the Chinese group revealed an experience-dependent response for pitch processing in the right hemisphere, consistent with a functionalaccount. The English group revealed a contralateral hemisphere preference consistent with a structuralaccount. At the brainstem level, Chinese participants showed a functional leftward ear asymmetry, whereas English were consistent with a structural account. Overall, language experience modulates both cortical hemispheric preference and brainstem ear asymmetry in a complementary manner to optimize processing of temporal attributes of pitch.
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http://dx.doi.org/10.1016/j.bandl.2021.104995DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8559596PMC
October 2021

Search for Electrophysiological Indices of Hidden Hearing Loss in Humans: Click Auditory Brainstem Response Across Sound Levels and in Background Noise.

Ear Hear 2021 Jan/Feb;42(1):53-67

Department of Speech, Language, and Hearing Sciences, Purdue University, West Lafayette, Indiana, USA.

Objectives: Recent studies in animals indicate that even moderate levels of exposure to noise can damage synaptic ribbons between the inner hair cells and auditory nerve fibers without affecting audiometric thresholds, giving rise to the use of the term "hidden hearing loss" (HHL). Despite evidence across several animal species, there is little consistent evidence for HHL in humans. The aim of the study is to evaluate potential electrophysiological changes specific to individuals at risk for HHL.

Design: Participants forming the high-risk experimental group consisted of 28 young normal-hearing adults who participated in marching band for at least 5 years. Twenty-eight age-matched normal-hearing adults who were not part of the marching band and had little or no history of recreational or occupational exposure to loud sounds formed the low-risk control group. Measurements included pure tone audiometry of conventional and high frequencies, distortion product otoacoustic emissions, and electrophysiological measures of auditory nerve and brainstem function as reflected in the click-evoked auditory brainstem response (ABR). In experiment 1, ABRs were recorded in a quiet background across stimulus levels (30-90 dB nHL) presented in 10 dB steps. In experiment 2, the ABR was elicited by a 70 dB nHL click stimulus presented in a quiet background, and in the presence of simultaneous ipsilateral continuous broadband noise presented at 50, 60, and 70 dB SPL using an insert earphone (Etymotic, ER2).

Results: There were no differences between the low- and high-risk groups in audiometric thresholds or distortion product otoacoustic emission amplitude. Experiment 1 demonstrated smaller wave-I amplitudes at moderate and high sound levels for high-risk compared to low-risk group with similar wave III and wave V amplitude. Enhanced amplitude ratio V/I, particularly at moderate sound level (60 dB nHL), suggesting central compensation for reduced input from the periphery for high-risk group. The results of experiment 2 show that the decrease in wave I amplitude with increasing background noise level was relatively smaller for the high-risk compared to the low-risk group. However, wave V amplitude reduction was essentially similar for both groups. These results suggest that masking induced wave I amplitude reduction is smaller in individuals at high risk for cochlear synaptopathy. Unlike previous studies, we did not observe a difference in the noise-induced wave V latency shift between low- and high-risk groups.

Conclusions: Results of experiment 1 are consistent with findings in both animal studies (that suggest cochlear synaptopathy involving selective damage of low-spontaneous rate and medium-spontaneous rate fibers), and in several human studies that show changes in a range of ABR metrics that suggest the presence of cochlear synaptopathy. However, without postmortem examination by harvesting human temporal bone (the gold standard for identifying synaptopathy) with different noise exposure background, no direct inferences can be derived for the presence/extent of cochlear synaptopathy in high-risk group with high sound over-exposure history. Results of experiment 2 demonstrate that to the extent response amplitude reflects both the number of neural elements responding and the neural synchrony of the responding elements, the relatively smaller change in response amplitude for the high-risk group would suggest a reduced susceptibility to masking. One plausible mechanism would be that suppressive effects that kick in at moderate to high levels are different in these two groups, particularly at moderate levels of the masking noise. Altogether, a larger scale dataset with different noise exposure background, longitudinal measurements (changes due to recreational over-exposure by studying middle-school to high-school students enrolled in marching band) with an array of behavioral and electrophysiological tests are needed to understand the complex pathogenesis of sound over-exposure damage in normal-hearing individuals.
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http://dx.doi.org/10.1097/AUD.0000000000000905DOI Listing
July 2021

Human Frequency Following Responses to Vocoded Speech: Amplitude Modulation Versus Amplitude Plus Frequency Modulation.

Ear Hear 2020 Mar/Apr;41(2):300-311

Department of Speech and Hearing Science, Arizona State University, Tempe, Arizona, USA.

Objectives: The most commonly employed speech processing strategies in cochlear implants (CIs) only extract and encode amplitude modulation (AM) in a limited number of frequency channels. proposed a novel speech processing strategy that encodes both frequency modulation (FM) and AM to improve CI performance. Using behavioral tests, they reported better speech, speaker, and tone recognition with this novel strategy than with the AM-alone strategy. Here, we used the scalp-recorded human frequency following responses (FFRs) to examine the differences in the neural representation of vocoded speech sounds with AM alone and AM + FM as the spectral and temporal cues were varied. Specifically, we were interested in determining whether the addition of FM to AM improved the neural representation of envelope periodicity (FFRENV) and temporal fine structure (FFRTFS), as reflected in the temporal pattern of the phase-locked neural activity generating the FFR.

Design: FFRs were recorded from 13 normal-hearing, adult listeners in response to the original unprocessed stimulus (a synthetic diphthong /au/ with a 110-Hz fundamental frequency or F0 and a 250-msec duration) and the 2-, 4-, 8- and 16-channel sine vocoded versions of /au/ with AM alone and AM + FM. Temporal waveforms, autocorrelation analyses, fast Fourier Transform, and stimulus-response spectral correlations were used to analyze both the strength and fidelity of the neural representation of envelope periodicity (F0) and TFS (formant structure).

Results: The periodicity strength in the FFRENV decreased more for the AM stimuli than for the relatively resilient AM + FM stimuli as the number of channels was increased. Regardless of the number of channels, a clear spectral peak of FFRENV was consistently observed at the stimulus F0 for all the AM + FM stimuli but not for the AM stimuli. Neural representation as revealed by the spectral correlation of FFRTFS was better for the AM + FM stimuli when compared to the AM stimuli. Neural representation of the time-varying formant-related harmonics as revealed by the spectral correlation was also better for the AM + FM stimuli as compared to the AM stimuli.

Conclusions: These results are consistent with previously reported behavioral results and suggest that the AM + FM processing strategy elicited brainstem neural activity that better preserved periodicity, temporal fine structure, and time-varying spectral information than the AM processing strategy. The relatively more robust neural representation of AM + FM stimuli observed here likely contributes to the superior performance on speech, speaker, and tone recognition with the AM + FM processing strategy. Taken together, these results suggest that neural information preserved in the FFR may be used to evaluate signal processing strategies considered for CIs.
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http://dx.doi.org/10.1097/AUD.0000000000000756DOI Listing
July 2021

Tone language experience-dependent advantage in pitch representation in brainstem and auditory cortex is maintained under reverberation.

Hear Res 2019 06 15;377:61-71. Epub 2019 Mar 15.

Purdue University, Department of Speech Language Hearing Sciences, Lyles-Porter Hall, 715 Clinic Drive, West Lafayette, IN 47907-2122, USA. Electronic address:

Long-term language and music experience enhances neural representation of temporal attributes of pitch in the brainstem and auditory cortex in favorable listening conditions. Herein we examine whether brainstem and cortical pitch mechanisms-shaped by long-term language experience-maintain this advantage in the presence of reverberation-induced degradation in pitch representation. Brainstem frequency following responses (FFR) and cortical pitch responses (CPR) were recorded concurrently from Chinese and English-speaking natives, using a Mandarin word exhibiting a high rising pitch (/yi/). Stimuli were presented diotically in quiet (Dry), and in the presence of Slight, Mild, and Moderate reverberation conditions. Regardless of language group, the amplitude of both brainstem FFR (F0) and cortical CPR (NaPb) responses decreased with increases in reverberation. Response amplitude for Chinese, however, was larger than English in all reverberant conditions. The Chinese group also exhibited a robust rightward asymmetry at temporal electrode sites (T8 > T7) across stimulus conditions. Regardless of language group, direct comparison of brainstem and cortical responses revealed similar magnitude of change in response amplitude with increasing reverberation. These findings suggest that experience-dependent brainstem and cortical pitch mechanisms provide an enhanced and stable neural representation of pitch-relevant information that is maintained even in the presence of reverberation. Relatively greater degradative effects of reverberation on brainstem (FFR) compared to cortical (NaPb) responses suggest relatively stronger top-down influences on CPRs.
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http://dx.doi.org/10.1016/j.heares.2019.03.009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6543830PMC
June 2019

Human frequency following responses to iterated rippled noise with positive and negative gain: Differential sensitivity to waveform envelope and temporal fine-structure.

Hear Res 2018 09 29;367:113-123. Epub 2018 Jul 29.

Department of Speech, Language, and Hearing Sciences, Purdue University, West Lafayette, IN, 47906, USA. Electronic address:

The perceived pitch of iterated rippled noise (IRN) with negative gain (IRNn) is an octave lower than that of IRN with positive gain (IRNp). IRNp and IRNn have identical waveform envelopes (ENV), but differing stimulus waveform fine structure (TFS), which likely accounts for this perceived pitch difference. Here, we examine whether differences in the temporal pattern of phase-locked activity reflected in the human brainstem Frequency Following Response (FFR) elicited by IRNp and IRNn can account for the differences in perceived pitch for the two stimuli. FFRs using a single onset polarity were measured in 13 normal-hearing, adult listeners in response to IRNp and IRNn stimuli with 2 ms, and 4 ms delay. Autocorrelation functions (ACFs) and Fast Fourier Transforms (FFTs) were used to evaluate the dominant periodicity and spectral pattern (harmonic spacing) in the phase-locked FFR neural activity. For both delays, the harmonic spacing in the spectra corresponded more strongly with the perceived lowering of pitch from IRNp to IRNn, compared to the ACFs. These results suggest that the FFR elicited by a single polarity stimulus reflects phase-locking to both stimulus ENV and TFS. A post-hoc experiment evaluating the FFR phase-locked activity to ENV (FFR), and TFS (FFR) elicited by IRNp and IRNn confirmed that only the phase-locked activity to the TFS, reflected in FFR, showed differences in both spectra and ACF that closely matched the pitch difference between the two stimuli. The results of the post-hoc experiment suggests that pitch-relevant information is preserved in the temporal pattern of phase-locked activity and suggests that the differences in stimulus ENV and TFS driving the pitch percept of IRNp and IRNn are preserved in the brainstem neural response. The scalp recorded FFR may provide for a noninvasive analytic tool to evaluate the relative contributions of envelope and temporal fine-structure in the neural representation of complex sounds in humans.
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http://dx.doi.org/10.1016/j.heares.2018.07.009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6130915PMC
September 2018

Language experience-dependent advantage in pitch representation in the auditory cortex is limited to favorable signal-to-noise ratios.

Hear Res 2017 11 14;355:42-53. Epub 2017 Sep 14.

Purdue University, Department of Speech Language Hearing Sciences, Lyles-Porter Hall, 715 Clinic Drive, West Lafayette, IN, 47907-2122, USA. Electronic address:

Long-term experience enhances neural representation of temporal attributes of pitch in the brainstem and auditory cortex in favorable listening conditions. Herein we examine whether cortical pitch mechanisms shaped by language experience are more resilient to degradation in background noise, and exhibit greater binaural release from masking (BRM). Cortical pitch responses (CPR) were recorded from Mandarin- and English-speaking natives using a Mandarin word exhibiting a high rising pitch (/yi/). Stimuli were presented diotically in Quiet, and in noise at +5, and 0 dB SNR. CPRs were also recorded in binaural conditions, SONO (where signal and noise were in phase at both ears); or S0Nπ (where signal was in phase and noise 180° out of phase at each ear), using 0 dB SNR. At Fz, both groups showed increase in CPR peak latency and decrease in amplitude with increasing noise level. A language-dependent enhancement of Na-Pb amplitude (Chinese > English) was restricted to Quiet and +5 dB SNR conditions. At T7/T8 electrode sites, Chinese natives exhibited a rightward asymmetry for both CPR components. A language-dependent effect (Chinese > English) was restricted to T8. Regarding BRM, both CPR components showed greater response amplitude for the S0Nπ condition compared to S0N0 across groups. Rightward asymmetry for BRM in the Chinese group indicates experience-dependent recruitment of right auditory cortex. Restriction of the advantage in pitch representation to the quiet and +5 SNR conditions, and the absence of group differences in the binaural release from masking, suggest that language experience affords limited advantage in the neural representation of pitch-relevant information in the auditory cortex under adverse listening conditions.
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http://dx.doi.org/10.1016/j.heares.2017.09.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5675814PMC
November 2017

Language-dependent changes in pitch-relevant neural activity in the auditory cortex reflect differential weighting of temporal attributes of pitch contours.

J Neurolinguistics 2017 Feb 16;41:38-49. Epub 2016 Sep 16.

Department of Speech Language Hearing Sciences, Purdue University, West Lafayette, IN USA.

There remains a gap in our knowledge base about neural representation of pitch attributes that occur between onset and offset of dynamic, curvilinear pitch contours. The aim is to evaluate how language experience shapes processing of pitch contours as reflected in the amplitude of cortical pitch-specific response components. Responses were elicited from three nonspeech, bidirectional (falling-rising) pitch contours representative of Mandarin Tone 2 varying in location of the turning point with fixed onset and offset. At the frontocentral Fz electrode site, Na-Pb and Pb-Nb amplitude of the Chinese group was larger than the English group for pitch contours exhibiting later location of the turning point relative to the one with the earliest location. Chinese listeners' amplitude was also greater than that of English in response to those same pitch contours with later turning points. At lateral temporal sites (T7/T8), Na-Pb amplitude was larger in Chinese listeners relative to English over the right temporal site. In addition, Pb-Nb amplitude of the Chinese group showed a rightward asymmetry. The pitch contour with its turning point located about halfway of total duration evoked a rightward asymmetry regardless of group. These findings suggest that neural mechanisms processing pitch in the right auditory cortex reflect experience-dependent modulation of sensitivity to weighted integration of changes in acceleration rates of rising and falling sections and the location of the turning point.
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http://dx.doi.org/10.1016/j.jneuroling.2016.09.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5507601PMC
February 2017

Human Frequency Following Responses to Vocoded Speech.

Ear Hear 2017 Sep/Oct;38(5):e256-e267

1Department of Audiology, Speech-Language Pathology, and Deaf Studies, Towson University, Towson, Maryland; 2Department of Speech, Language, and Hearing Sciences, Purdue University, West Lafayette, Indiana; and 3Department of Speech and Hearing Science, Arizona State University, Tempe, Arizona.

Objectives: Vocoders offer an effective platform to simulate the effects of cochlear implant speech processing strategies in normal-hearing listeners. Several behavioral studies have examined the effects of varying spectral and temporal cues on vocoded speech perception; however, little is known about the neural indices of vocoded speech perception. Here, the scalp-recorded frequency following response (FFR) was used to study the effects of varying spectral and temporal cues on brainstem neural representation of specific acoustic cues, the temporal envelope periodicity related to fundamental frequency (F0) and temporal fine structure (TFS) related to formant and formant-related frequencies, as reflected in the phase-locked neural activity in response to vocoded speech.

Design: In experiment 1, FFRs were measured in 12 normal-hearing, adult listeners in response to a steady state English back vowel /u/ presented in an unaltered, unprocessed condition and six sine-vocoder conditions with varying numbers of channels (1, 2, 4, 8, 16, and 32), while the temporal envelope cutoff frequency was fixed at 500 Hz. In experiment 2, FFRs were obtained from 14 normal-hearing, adult listeners in response to the same English vowel /u/, presented in an unprocessed condition and four vocoded conditions where both the temporal envelope cutoff frequency (50 versus 500 Hz) and carrier type (sine wave versus noise band) were varied separately with the number of channels fixed at 8. Fast Fourier Transform was applied to the time waveforms of FFR to analyze the strength of brainstem neural representation of temporal envelope periodicity (F0) and TFS-related peaks (formant structure).

Results: Brainstem neural representation of both temporal envelope and TFS cues improved when the number of channels increased from 1 to 4, followed by a plateau with 8 and 16 channels, and a reduction in phase-locking strength with 32 channels. For the sine vocoders, peaks in the FFRTFS spectra corresponded with the low-frequency sine-wave carriers and side band frequencies in the stimulus spectra. When the temporal envelope cutoff frequency increased from 50 to 500 Hz, an improvement was observed in brainstem F0 representation with no change in brainstem representation of spectral peaks proximal to the first formant frequency (F1). There was no significant effect of carrier type (sine- versus noise-vocoder) on brainstem neural representation of F0 cues when the temporal envelope cutoff frequency was 500 Hz.

Conclusions: While the improvement in neural representation of temporal envelope and TFS cues with up to 4 vocoder channels is consistent with the behavioral literature, the reduced neural phase-locking strength noted with even more channels may be because of the narrow bandwidth of each channel as the number of channels increases. Stronger neural representation of temporal envelope cues with higher temporal envelope cutoff frequencies is likely a reflection of brainstem neural phase-locking to F0-related periodicity fluctuations preserved in the 500-Hz temporal envelopes, which are unavailable in the 50-Hz temporal envelopes. No effect of temporal envelope cutoff frequency was seen for neural representation of TFS cues, suggesting that spectral side band frequencies created by the 500-Hz temporal envelopes did not improve neural representation of F1 cues over the 50-Hz temporal envelopes. Finally, brainstem F0 representation was not significantly affected by carrier type with a temporal envelope cutoff frequency of 500 Hz, which is inconsistent with previous results of behavioral studies examining pitch perception of vocoded stimuli.
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http://dx.doi.org/10.1097/AUD.0000000000000432DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5570627PMC
May 2018

Differential sensitivity to changes in pitch acceleration in the auditory brainstem and cortex.

Brain Lang 2017 06 24;169:22-27. Epub 2017 Feb 24.

Department of Speech Language Hearing Sciences, Purdue University, USA. Electronic address:

The cortical pitch-specific response (CPR) is differentially sensitive to pitch contours varying in rate of acceleration-time-variant Mandarin Tone2 (T2) versus constant, linear rising ramp (Linear)-as a function of language experience (Krishnan, Gandour, & Suresh, 2014). CPR and brainstem frequency following response (FFR) data were recorded concurrently from native Mandarin listeners using the same stimuli. Results showed that T2 elicited larger responses than Linear at both cortical and brainstem levels (CPR: Na-Pb, Pb-Nb; FFR). However, Pb-Nb exhibited a larger difference in magnitude between T2 and Linear than either Na-Pb or FFR. This finding highlights differential weighting of brain responses elicited by a specific temporal attribute of pitch. Consistent with the notion of a distributed, integrated hierarchical pitch processing network, temporal attributes of pitch are differentially weighted by subcortical and cortical level processing.
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http://dx.doi.org/10.1016/j.bandl.2017.01.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5425296PMC
June 2017

Changes in pitch height elicit both language-universal and language-dependent changes in neural representation of pitch in the brainstem and auditory cortex.

Neuroscience 2017 03 17;346:52-63. Epub 2017 Jan 17.

Purdue University, Department of Speech Language Hearing Sciences, Lyles-Porter Hall, 715 Clinic Drive, West Lafayette, IN 47907-2122, USA. Electronic address:

Language experience shapes encoding of pitch-relevant information at both brainstem and cortical levels of processing. Pitch height is a salient dimension that orders pitch from low to high. Herein we investigate the effects of language experience (Chinese, English) in the brainstem and cortex on (i) neural responses to variations in pitch height, (ii) presence of asymmetry in cortical pitch representation, and (iii) patterns of relative changes in magnitude of pitch height between these two levels of brain structure. Stimuli were three nonspeech homologs of Mandarin Tone 2 varying in pitch height only. The frequency-following response (FFR) and the cortical pitch-specific response (CPR) were recorded concurrently. At the Fz-linked T7/T8 site, peak latency of Na, Pb, and Nb decreased with increasing pitch height for both groups. Peak-to-peak amplitude of Na-Pb and Pb-Nb increased with increasing pitch height across groups. A language-dependent effect was restricted to Na-Pb; the Chinese had larger amplitude than the English group. At temporal sites (T7/T8), the Chinese group had larger amplitude, as compared to English, across stimuli, but also limited to the Na-Pb component and right temporal site. In the brainstem, F0 magnitude decreased with increasing pitch height; Chinese had larger magnitude across stimuli. A comparison of CPR and FFR responses revealed distinct patterns of relative changes in magnitude common to both groups. CPR amplitude increased and FFR amplitude decreased with increasing pitch height. Experience-dependent effects on CPR components vary as a function of neural sensitivity to pitch height within a particular temporal window (Na-Pb). Differences between the auditory brainstem and cortex imply distinct neural mechanisms for pitch extraction at both levels of brain structure.
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http://dx.doi.org/10.1016/j.neuroscience.2017.01.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5337167PMC
March 2017

Corrigendum to ''Language-experience plasticity in neural representation of changes in pitch salience'' [Brain Research 1637 (2016) 102-117].

Brain Res 2016 Aug 11;1644:308. Epub 2016 May 11.

Department of Speech Language Hearing Sciences, Purdue University, USA.

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http://dx.doi.org/10.1016/j.brainres.2016.05.004DOI Listing
August 2016

Language-experience plasticity in neural representation of changes in pitch salience.

Brain Res 2016 Apr 20;1637:102-117. Epub 2016 Feb 20.

Department of Speech Language Hearing Sciences, Purdue University, Lyles Porter Hall, 715 Clinic Drive, West Lafayette, IN 47907-2122, USA. Electronic address:

Neural representation of pitch-relevant information at the brainstem and cortical levels of processing is influenced by language experience. A well-known attribute of pitch is its salience. Brainstem frequency following responses and cortical pitch specific responses, recorded concurrently, were elicited by a pitch salience continuum spanning weak to strong pitch of a dynamic, iterated rippled noise pitch contour-homolog of a Mandarin tone. Our aims were to assess how language experience (Chinese, English) affects i) enhancement of neural activity associated with pitch salience at brainstem and cortical levels, ii) the presence of asymmetry in cortical pitch representation, and iii) patterns of relative changes in magnitude along the pitch salience continuum. Peak latency (Fz: Na, Pb, and Nb) was shorter in the Chinese than the English group across the continuum. Peak-to-peak amplitude (Fz: Na-Pb, Pb-Nb) of the Chinese group grew larger with increasing pitch salience, but an experience-dependent advantage was limited to the Na-Pb component. At temporal sites (T7/T8), the larger amplitude of the Chinese group across the continuum was both limited to the Na-Pb component and the right temporal site. At the brainstem level, F0 magnitude gets larger as you increase pitch salience, and it too reveals Chinese superiority. A direct comparison of cortical and brainstem responses for the Chinese group reveals different patterns of relative changes in magnitude along the pitch salience continuum. Such differences may point to a transformation in pitch processing at the cortical level presumably mediated by local sensory and/or extrasensory influence overlaid on the brainstem output.
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http://dx.doi.org/10.1016/j.brainres.2016.02.021DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4821701PMC
April 2016

Human Frequency Following Response: Neural Representation of Envelope and Temporal Fine Structure in Listeners with Normal Hearing and Sensorineural Hearing Loss.

Ear Hear 2016 Mar-Apr;37(2):e91-e103

1Department of Speech Language Hearing Sciences, Purdue University, West Lafayette, Indiana, USA; 2Department of Audiology, Speech-Language Pathology and Deaf studies, Towson University, Towson, Maryland, USA; 3Department of Biomedical Engineering, Purdue University, West Lafayette, Indiana, USA; and 4Department of Biological Sciences, Purdue University, West Lafayette, Indiana, USA.

Objective: Listeners with sensorineural hearing loss (SNHL) typically experience reduced speech perception, which is not completely restored with amplification. This likely occurs because cochlear damage, in addition to elevating audiometric thresholds, alters the neural representation of speech transmitted to higher centers along the auditory neuroaxis. While the deleterious effects of SNHL on speech perception in humans have been well-documented using behavioral paradigms, our understanding of the neural correlates underlying these perceptual deficits remains limited. Using the scalp-recorded frequency following response (FFR), the authors examine the effects of SNHL and aging on subcortical neural representation of acoustic features important for pitch and speech perception, namely the periodicity envelope (F0) and temporal fine structure (TFS; formant structure), as reflected in the phase-locked neural activity generating the FFR.

Design: FFRs were obtained from 10 listeners with normal hearing (NH) and 9 listeners with mild-moderate SNHL in response to a steady-state English back vowel /u/ presented at multiple intensity levels. Use of multiple presentation levels facilitated comparisons at equal sound pressure level (SPL) and equal sensation level. In a second follow-up experiment to address the effect of age on envelope and TFS representation, FFRs were obtained from 25 NH and 19 listeners with mild to moderately severe SNHL to the same vowel stimulus presented at 80 dB SPL. Temporal waveforms, Fast Fourier Transform and spectrograms were used to evaluate the magnitude of the phase-locked activity at F0 (periodicity envelope) and F1 (TFS).

Results: Neural representation of both envelope (F0) and TFS (F1) at equal SPLs was stronger in NH listeners compared with listeners with SNHL. Also, comparison of neural representation of F0 and F1 across stimulus levels expressed in SPL and sensation level (accounting for audibility) revealed that level-related changes in F0 and F1 magnitude were different for listeners with SNHL compared with listeners with NH. Furthermore, the degradation in subcortical neural representation was observed to persist in listeners with SNHL even when the effects of age were controlled for.

Conclusions: Overall, our results suggest a relatively greater degradation in the neural representation of TFS compared with periodicity envelope in individuals with SNHL. This degraded neural representation of TFS in SNHL, as reflected in the brainstem FFR, may reflect a disruption in the temporal pattern of phase-locked neural activity arising from altered tonotopic maps and/or wider filters causing poor frequency selectivity in these listeners. Finally, while preliminary results indicate that the deleterious effects of SNHL may be greater than age-related degradation in subcortical neural representation, the lack of a balanced age-matched control group in this study does not permit us to completely rule out the effects of age on subcortical neural representation.
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http://dx.doi.org/10.1097/AUD.0000000000000247DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4767571PMC
December 2016

Pitch processing of dynamic lexical tones in the auditory cortex is influenced by sensory and extrasensory processes.

Eur J Neurosci 2015 May 6;41(11):1496-504. Epub 2015 May 6.

Department of Speech Language Hearing Sciences, Purdue University, Lyles-Porter Hall, 715 Clinic Drive, West Lafayette, IN, 47907, USA.

The aim is to evaluate how language experience (Chinese, English) shapes processing of pitch contours as reflected in the amplitude of cortical pitch response components. Responses were elicited from three dynamic curvilinear nonspeech stimuli varying in pitch direction and location of peak acceleration: Mandarin lexical Tone 2 (rising) and Tone 4 (falling), and a flipped variant of Tone 2, Tone 2' (nonnative). At temporal sites (T7/T8), Chinese listeners' Na-Pb response amplitudes to Tones 2 and 4 were greater than those of English listeners in the right hemisphere only; a rightward asymmetry for Tones 2 and 4 was restricted to the Chinese group. In common to both Fz-to-linked T7/T8 and T7/T8 electrode sites, the stimulus pattern (Tones 2 and 4 > Tone 2') was found in the Chinese group only. As reflected by Pb-Nb at Fz, Chinese subjects' amplitudes were larger than those of English subjects in response to Tones 2 and 4, and Tones 2 and 4 were larger than Tone 2', whereas for English subjects, Tone 2 was larger than Tone 2' and Tone 4. At frontal electrode sites (F3/F4), regardless of component or hemisphere, Chinese subjects' responses were larger in amplitude than those of English subjects across stimuli. For either group, responses to Tones 2 and 4 were larger than Tone 2'. No hemispheric asymmetry was observed at the frontal electrode sites. These findings demonstrate that cortical pitch response components are differentially modulated by experience-dependent, temporally distinct but functionally overlapping, weighting of sensory and extrasensory effects on pitch processing of lexical tones in the right temporal lobe and, more broadly, are consistent with a distributed hierarchical predictive coding process.
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http://dx.doi.org/10.1111/ejn.12903DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4461533PMC
May 2015

LANGUAGE EXPERIENCE SHAPES PROCESSING OF PITCH RELEVANT INFORMATION IN THE HUMAN BRAINSTEM AND AUDITORY CORTEX: ELECTROPHYSIOLOGICAL EVIDENCE.

Acoust Aust 2014 Dec;42(3):166-178

Department of Speech Language Hearing Sciences, Purdue University, West Lafayette, IN 47907, USA.

Pitch is a robust perceptual attribute that plays an important role in speech, language, and music. As such, it provides an analytic window to evaluate how neural activity relevant to pitch undergo transformation from early sensory to later cognitive stages of processing in a well coordinated hierarchical network that is subject to experience-dependent plasticity. We review recent evidence of language experience-dependent effects in pitch processing based on comparisons of native vs. nonnative speakers of a tonal language from electrophysiological recordings in the auditory brainstem and auditory cortex. We present evidence that shows enhanced representation of linguistically-relevant pitch dimensions or features at both the brainstem and cortical levels with a stimulus-dependent preferential activation of the right hemisphere in native speakers of a tone language. We argue that neural representation of pitch-relevant information in the brainstem and early sensory level processing in the auditory cortex is shaped by the perceptual salience of domain-specific features. While both stages of processing are shaped by language experience, neural representations are transformed and fundamentally different at each biological level of abstraction. The representation of pitch relevant information in the brainstem is more fine-grained spectrotemporally as it reflects sustained neural phase-locking to pitch relevant periodicities contained in the stimulus. In contrast, the cortical pitch relevant neural activity reflects primarily a series of transient temporal neural events synchronized to certain temporal attributes of the pitch contour. We argue that experience-dependent enhancement of pitch representation for Chinese listeners most likely reflects an interaction between higher-level cognitive processes and early sensory-level processing to improve representations of behaviorally-relevant features that contribute optimally to perception. It is our view that long-term experience shapes this adaptive process wherein the top-down connections provide selective gating of inputs to both cortical and subcortical structures to enhance neural responses to specific behaviorally-relevant attributes of the stimulus. A theoretical framework for a neural network is proposed involving coordination between local, feedforward, and feedback components that can account for experience-dependent enhancement of pitch representations at multiple levels of the auditory pathway. The ability to record brainstem and cortical pitch relevant responses concurrently may provide a new window to evaluate the online interplay between feedback, feedforward, and local intrinsic components in the hierarchical processing of pitch relevant information.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4380086PMC
December 2014

Language experience enhances early cortical pitch-dependent responses.

J Neurolinguistics 2015 Feb;33:128-148

School of Mechanical Engineering, Purdue University, West Lafayette, IN, USA.

Pitch processing at cortical and subcortical stages of processing is shaped by language experience. We recently demonstrated that specific components of the cortical pitch response (CPR) index the more rapidly-changing portions of the high rising Tone 2 of Mandarin Chinese, in addition to marking pitch onset and sound offset. In this study, we examine how language experience (Mandarin vs. English) shapes the processing of different temporal attributes of pitch reflected in the CPR components using stimuli representative of within-category variants of Tone 2. Results showed that the magnitude of CPR components (Na-Pb and Pb-Nb) and the correlation between these two components and pitch acceleration were stronger for the Chinese listeners compared to English listeners for stimuli that fell within the range of Tone 2 citation forms. Discriminant function analysis revealed that the Na-Pb component was more than twice as important as Pb-Nb in grouping listeners by language affiliation. In addition, a stronger stimulus-dependent, rightward asymmetry was observed for the Chinese group at the temporal, but not frontal, electrode sites. This finding may reflect selective recruitment of experience-dependent, pitch-specific mechanisms in right auditory cortex to extract more complex, time-varying pitch patterns. Taken together, these findings suggest that long-term language experience shapes early sensory level processing of pitch in the auditory cortex, and that the sensitivity of the CPR may vary depending on the relative linguistic importance of specific temporal attributes of dynamic pitch.
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http://dx.doi.org/10.1016/j.jneuroling.2014.08.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4261237PMC
February 2015

Cortical pitch response components show differential sensitivity to native and nonnative pitch contours.

Brain Lang 2014 Nov 10;138:51-60. Epub 2014 Oct 10.

Department of Speech Language Hearing Sciences, Purdue University, USA. Electronic address:

The aim of this study is to evaluate how nonspeech pitch contours of varying shape influence latency and amplitude of cortical pitch-specific response (CPR) components differentially as a function of language experience. Stimuli included time-varying, high rising Mandarin Tone 2 (T2) and linear rising ramp (Linear), and steady-state (Flat). Both the latency and magnitude of CPR components were differentially modulated by (i) the overall trajectory of pitch contours (time-varying vs. steady-state), (ii) their pitch acceleration rates (changing vs. constant), and (iii) their linguistic status (lexical vs. non-lexical). T2 elicited larger amplitude than Linear in both language groups, but size of the effect was larger in Chinese than English. The magnitude of CPR components elicited by T2 were larger for Chinese than English at the right temporal electrode site. Using the CPR, we provide evidence in support of experience-dependent modulation of dynamic pitch contours at an early stage of sensory processing.
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http://dx.doi.org/10.1016/j.bandl.2014.09.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4335674PMC
November 2014

Cortical pitch response components index stimulus onset/offset and dynamic features of pitch contours.

Neuropsychologia 2014 Jul 18;59:1-12. Epub 2014 Apr 18.

School of Mechanical Engineering, Purdue University, West Lafayette, IN, USA. Electronic address:

Voice pitch is an important information-bearing component of language that is subject to experience dependent plasticity at both early cortical and subcortical stages of processing. We have already demonstrated that pitch onset component (Na) of the cortical pitch response (CPR) is sensitive to flat pitch and its salience … CPR responses from Chinese listeners were elicited by three citation forms varying in pitch acceleration and duration. Results showed that the pitch onset component (Na) was invariant to changes in acceleration. In contrast, Na–Pb and Pb–Nb showed a systematic decrease in the interpeak latency and decrease in amplitude with increase in pitch acceleration that followed the time course of pitch change across the three stimuli. A strong correlation with pitch acceleration was observed for these two components only – a putative index of pitch-relevant neural activity associated with the more rapidly-changing portions of the pitch contour. Pc–Nc marks unambiguously the stimulus offset … and their functional roles as related to sensory and cognitive properties of the stimulus. [Corrected]
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http://dx.doi.org/10.1016/j.neuropsychologia.2014.04.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4169671PMC
July 2014

Phase locked neural activity in the human brainstem predicts preference for musical consonance.

Neuropsychologia 2014 May 29;58:23-32. Epub 2014 Mar 29.

School of Psychological Sciences, The University of Manchester, Manchester M13 9PL, UK.

When musical notes are combined to make a chord, the closeness of fit of the combined spectrum to a single harmonic series (the 'harmonicity' of the chord) predicts the perceived consonance (how pleasant and stable the chord sounds; McDermott, Lehr, & Oxenham, 2010). The distinction between consonance and dissonance is central to Western musical form. Harmonicity is represented in the temporal firing patterns of populations of brainstem neurons. The current study investigates the role of brainstem temporal coding of harmonicity in the perception of consonance. Individual preference for consonant over dissonant chords was measured using a rating scale for pairs of simultaneous notes. In order to investigate the effects of cochlear interactions, notes were presented in two ways: both notes to both ears or each note to different ears. The electrophysiological frequency following response (FFR), reflecting sustained neural activity in the brainstem synchronised to the stimulus, was also measured. When both notes were presented to both ears the perceptual distinction between consonant and dissonant chords was stronger than when the notes were presented to different ears. In the condition in which both notes were presented to the both ears additional low-frequency components, corresponding to difference tones resulting from nonlinear cochlear processing, were observable in the FFR effectively enhancing the neural harmonicity of consonant chords but not dissonant chords. Suppressing the cochlear envelope component of the FFR also suppressed the additional frequency components. This suggests that, in the case of consonant chords, difference tones generated by interactions between notes in the cochlea enhance the perception of consonance. Furthermore, individuals with a greater distinction between consonant and dissonant chords in the FFR to individual harmonics had a stronger preference for consonant over dissonant chords. Overall, the results provide compelling evidence for the role of neural temporal coding in the perception of consonance, and suggest that the representation of harmonicity in phase locked neural firing drives the perception of consonance.
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http://dx.doi.org/10.1016/j.neuropsychologia.2014.03.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4040538PMC
May 2014

Relationship between brainstem, cortical and behavioral measures relevant to pitch salience in humans.

Neuropsychologia 2012 Oct 23;50(12):2849-2859. Epub 2012 Aug 23.

Department of Speech Language Hearing Sciences, Purdue University, West Lafayette, IN 47907-2038, USA. Electronic address:

Neural representation of pitch-relevant information at both the brainstem and cortical levels of processing is influenced by language or music experience. However, the functional roles of brainstem and cortical neural mechanisms in the hierarchical network for language processing, and how they drive and maintain experience-dependent reorganization are not known. In an effort to evaluate the possible interplay between these two levels of pitch processing, we introduce a novel electrophysiological approach to evaluate pitch-relevant neural activity at the brainstem and auditory cortex concurrently. Brainstem frequency-following responses and cortical pitch responses were recorded from participants in response to iterated rippled noise stimuli that varied in stimulus periodicity (pitch salience). A control condition using iterated rippled noise devoid of pitch was employed to ensure pitch specificity of the cortical pitch response. Neural data were compared with behavioral pitch discrimination thresholds. Results showed that magnitudes of neural responses increase systematically and that behavioral pitch discrimination improves with increasing stimulus periodicity, indicating more robust encoding for salient pitch. Absence of cortical pitch response in the control condition confirms that the cortical pitch response is specific to pitch. Behavioral pitch discrimination was better predicted by brainstem and cortical responses together as compared to each separately. The close correspondence between neural and behavioral data suggest that neural correlates of pitch salience that emerge in early, preattentive stages of processing in the brainstem may drive and maintain with high fidelity the early cortical representations of pitch. These neural representations together contain adequate information for the development of perceptual pitch salience.
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http://dx.doi.org/10.1016/j.neuropsychologia.2012.08.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3483071PMC
October 2012

Distortion products and their influence on representation of pitch-relevant information in the human brainstem for unresolved harmonic complex tones.

Hear Res 2012 Oct 14;292(1-2):26-34. Epub 2012 Aug 14.

School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN 47907-2038, USA.

Pitch experiments aimed at evaluating temporal pitch mechanism(s) often utilize complex sounds with only unresolved harmonic components, and a low-pass noise masker to eliminate the potential contribution of audible distortion products to the pitch percept. Herein we examine how: (i) masker induced reduction of neural distortion products (difference tone: DT; and cubic difference tone: CDT) alters the representation of pitch relevant information in the brainstem; and (ii) the pitch salience is altered when distortion products are reduced and/or eliminated. Scalp recorded brainstem frequency following responses (FFR) were recorded in normal hearing individuals using a complex tone with only unresolved harmonics presented in quiet, and in the presence of a low-pass masker at SNRs of +15, +5, and -5 dB. Difference limen for F0 discrimination (F0 DL) was obtained in quiet and in the presence of low-pass noise. Magnitude of DT components (with the exception of components at F0 and 2F0), and the CDT components decreased with increasing masker level. Neural pitch strength decreased with increasing masker level for both the envelope-related (FFR(ENV)) and spectral-related (FFR(SPEC)) phase-locked activity. Finally, F0 DLs increased with decreasing SNRs suggesting poorer F0 discrimination with reduction of the distortion products. Collectively, these findings support the notion that both DT and CDT, as reflected in the FFR(ENV) and FFR(SPEC), respectively, influence both the brainstem representation of pitch relevant information and the pitch salience of the complex sounds.
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http://dx.doi.org/10.1016/j.heares.2012.08.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3483078PMC
October 2012

Experience-dependent plasticity in pitch encoding: from brainstem to auditory cortex.

Neuroreport 2012 May;23(8):498-502

Department of Speech Language Hearing Sciences, Purdue University, West Lafayette, Indiana, USA.

Linguistic and musical pitch provide an analytic window to evaluate how neural representations of important pitch attributes of a sound undergo transformation from early sensory to later cognitive stages of processing in the human brain, and how pitch-relevant experience shapes these representations. These pitch attributes are shaped differentially depending on their functional relevance to a listener. Neural encoding of pitch-relevant information is shaped by the perceptual salience of domain-specific features at subcortical (auditory brainstem) and cortical stages of processing. The emergence of a functional ear asymmetry in the neural encoding of pitch-relevant information at a lower sensory processing level supports the view that local and feedforward and feedback mechanisms are involved in pitch-relevant processing. A theoretical framework for a neural network is proposed involving coordination between local, feedforward, and feedback components that can account for experience-induced enhancement of pitch representations at multiple levels of the auditory pathway.
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http://dx.doi.org/10.1097/WNR.0b013e328353764dDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3342423PMC
May 2012

Linguistic status of timbre influences pitch encoding in the brainstem.

Neuroreport 2011 Nov;22(16):801-3

Department of Speech Language Hearing Sciences, Purdue University, West Lafayette, Indiana 47907-2038, USA.

The aim of this experiment is to assess the effects of the linguistic status of timbre on pitch processing in the brainstem. Brainstem frequency following responses were evoked by the Mandarin high-rising lexical tone superimposed on a native vowel quality ([i]), nonnative vowel quality ([œ]), and iterated rippled noise (nonspeech). Results revealed that voice fundamental frequency magnitudes were larger when concomitant with a native vowel quality compared with either nonnative vowel quality or nonspeech timbre. Such experience-dependent effects suggest that subcortical sensory encoding of pitch interacts with timbre in the human brainstem. As a consequence, responses of the perceptual system can be differentially shaped to pitch patterns in relation to the linguistic status of their concomitant timbre.
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http://dx.doi.org/10.1097/WNR.0b013e32834b2996DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3188353PMC
November 2011

Musicians demonstrate experience-dependent brainstem enhancement of musical scale features within continuously gliding pitch.

Neurosci Lett 2011 Oct 30;503(3):203-7. Epub 2011 Aug 30.

Department of Speech, Language, and Hearing Sciences, Purdue University, W. Lafayette, IN 47907, USA.

In contrast to language, where pitch patterns consist of continuous and curvilinear contours, musical pitch consists of relatively discrete, stair-stepped sequences of notes. Behavioral and neurophysiological studies suggest that both tone-language and music experience enhance the representation of pitch cues associated with a listener's domain of expertise, e.g., curvilinear pitch in language, discrete scale steps in music. We compared brainstem frequency-following responses (FFRs) of English-speaking musicians (musical pitch experience) and native speakers of Mandarin Chinese (linguistic pitch experience) elicited by rising and falling tonal sweeps that are exemplary of Mandarin tonal contours but uncharacteristic of the pitch patterns typically found in music. In spite of musicians' unfamiliarity with such glides, we find that their brainstem FFRs show enhancement of the stimulus where the curvilinear sweep traverses discrete notes along the diatonic musical scale. This enhancement was note specific in that it was not observed immediately preceding or following the scale tone of interest (passing note). No such enhancements were observed in Chinese listeners. These findings suggest that the musician's brainstem may be differentially tuned by long-term exposure to the pitch patterns inherent to music, extracting pitch in relation to a fixed, hierarchical scale.
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http://dx.doi.org/10.1016/j.neulet.2011.08.036DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3196385PMC
October 2011

Musicians and tone-language speakers share enhanced brainstem encoding but not perceptual benefits for musical pitch.

Brain Cogn 2011 Oct 10;77(1):1-10. Epub 2011 Aug 10.

Department of Speech, Language, and Hearing Sciences, Purdue University, W. Lafayette, IN 47907, USA.

Behavioral and neurophysiological transfer effects from music experience to language processing are well-established but it is currently unclear whether or not linguistic expertise (e.g., speaking a tone language) benefits music-related processing and its perception. Here, we compare brainstem responses of English-speaking musicians/non-musicians and native speakers of Mandarin Chinese elicited by tuned and detuned musical chords, to determine if enhancements in subcortical processing translate to improvements in the perceptual discrimination of musical pitch. Relative to non-musicians, both musicians and Chinese had stronger brainstem representation of the defining pitches of musical sequences. In contrast, two behavioral pitch discrimination tasks revealed that neither Chinese nor non-musicians were able to discriminate subtle changes in musical pitch with the same accuracy as musicians. Pooled across all listeners, brainstem magnitudes predicted behavioral pitch discrimination performance but considering each group individually, only musicians showed connections between neural and behavioral measures. No brain-behavior correlations were found for tone language speakers or non-musicians. These findings point to a dissociation between subcortical neurophysiological processing and behavioral measures of pitch perception in Chinese listeners. We infer that sensory-level enhancement of musical pitch information yields cognitive-level perceptual benefits only when that information is behaviorally relevant to the listener.
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http://dx.doi.org/10.1016/j.bandc.2011.07.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3159732PMC
October 2011

Functional ear (a)symmetry in brainstem neural activity relevant to encoding of voice pitch: a precursor for hemispheric specialization?

Brain Lang 2011 Dec 11;119(3):226-31. Epub 2011 Jun 11.

Department of Speech Language Hearing Sciences, Purdue University, West Lafayette, IN, USA 47907-2038, USA.

Pitch processing is lateralized to the right hemisphere; linguistic pitch is further mediated by left cortical areas. This experiment investigates whether ear asymmetries vary in brainstem representation of pitch depending on linguistic status. Brainstem frequency-following responses (FFRs) were elicited by monaural stimulation of the left and right ear of 15 native speakers of Mandarin Chinese using two synthetic speech stimuli that differ in linguistic status of tone. One represented a native lexical tone (Tone 2: T2); the other, T2', a nonnative variant in which the pitch contour was a mirror image of T2 with the same starting and ending frequencies. Two 40-ms portions of f(0) contours were selected in order to compare two regions (R1, early; R2 late) differing in pitch acceleration rate and perceptual saliency. In R2, linguistic status effects revealed that T2 exhibited a larger degree of FFR rightward ear asymmetry as reflected in f(0) amplitude relative to T2'. Relative to midline (ear asymmetry=0), the only ear asymmetry reaching significance was that favoring left ear stimulation elicited by T2'. By left- and right-ear stimulation separately, FFRs elicited by T2 were larger than T2' in the right ear only. Within T2', FFRs elicited by the earlier region were larger than the later in both ears. Within T2, no significant differences in FFRS were observed between regions in either ear. Collectively, these findings support the idea that origins of cortical processing preferences for perceptually-salient portions of pitch are rooted in early, preattentive stages of processing in the brainstem.
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http://dx.doi.org/10.1016/j.bandl.2011.05.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3193894PMC
December 2011

Brainstem correlates of behavioral and compositional preferences of musical harmony.

Neuroreport 2011 Mar;22(5):212-6

Department of Speech, Language, & Hearing Sciences, Purdue University, West Lafayette, Indiana, USA.

Certain chords are preferred by listeners behaviorally and also occur with higher regularity in musical composition. Event-related potentials index the perceived consonance (i.e., pleasantness) of musical pitch relationships providing a cortical neural correlate for such behavioral preferences. Here, we show correlates of these harmonic preferences exist at subcortical stages of audition. Brainstem frequency-following responses were measured in response to four prototypical musical triads. Pitch salience computed from frequency-following responses correctly predicted the ordering of triadic harmony stipulated by music theory (i.e., major >minor >>diminished >augmented). Moreover, neural response magnitudes showed high correspondence with listeners' perceptual ratings of the same chords. Results suggest that preattentive stages of pitch processing may contribute to perceptual judgments of musical harmony.
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http://dx.doi.org/10.1097/WNR.0b013e328344a689DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3057421PMC
March 2011

Enhanced brainstem encoding predicts musicians' perceptual advantages with pitch.

Eur J Neurosci 2011 Feb 29;33(3):530-8. Epub 2010 Dec 29.

Department of Speech Language Hearing Sciences, Purdue University, West Lafayette, IN, USA.

Important to Western tonal music is the relationship between pitches both within and between musical chords; melody and harmony are generated by combining pitches selected from the fixed hierarchical scales of music. It is of critical importance that musicians have the ability to detect and discriminate minute deviations in pitch in order to remain in tune with other members of their ensemble. Event-related potentials indicate that cortical mechanisms responsible for detecting mistuning and violations in pitch are more sensitive and accurate in musicians as compared with non-musicians. The aim of the present study was to address whether this superiority is also present at a subcortical stage of pitch processing. Brainstem frequency-following responses were recorded from musicians and non-musicians in response to tuned (i.e. major and minor) and detuned (± 4% difference in frequency) chordal arpeggios differing only in the pitch of their third. Results showed that musicians had faster neural synchronization and stronger brainstem encoding for defining characteristics of musical sequences regardless of whether they were in or out of tune. In contrast, non-musicians had relatively strong representation for major/minor chords but showed diminished responses for detuned chords. The close correspondence between the magnitude of brainstem responses and performance on two behavioral pitch discrimination tasks supports the idea that musicians' enhanced detection of chordal mistuning may be rooted at pre-attentive, sensory stages of processing. Findings suggest that perceptually salient aspects of musical pitch are not only represented at subcortical levels but that these representations are also enhanced by musical experience.
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http://dx.doi.org/10.1111/j.1460-9568.2010.07527.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3059719PMC
February 2011

Neural encoding in the human brainstem relevant to the pitch of complex tones.

Hear Res 2011 May 16;275(1-2):110-9. Epub 2010 Dec 16.

Department of Speech Language Hearing Sciences, Purdue University, 1353 Heavilon Hall, 500 Oval Drive, West Lafayette, IN 47907-2038, USA.

Psychoacoustic studies have shown that complex tones containing resolved harmonics evoke stronger pitches than complex tones with only unresolved harmonics. Also, unresolved harmonics presented in alternating sine and cosine (ALT) phase produce a doubling of pitch. We examine here whether the temporal pattern of phase-locked neural activity reflected in the scalp recorded human frequency following response (FFR) preserves information relevant to pitch strength, and to the doubling of pitch for ALT stimuli. Results revealed stronger neural periodicity strength for resolved stimuli, although the effect of resolvability was weak compared to the effect observed behaviorally; autocorrelation functions and FFR spectra suggest a different pattern of phase-locked neural activity for ALT stimuli with resolved and unresolved harmonics consistent with the doubling of pitch observed in our behavioral estimates; and the temporal pattern of neural activity underlying pitch encoding appears to be similar at the auditory nerve (auditory nerve model response) and the rostral brainstem level (FFR). These findings suggest that the phase-locked neural activity reflected in the scalp recorded FFR preserves neural information relevant to pitch that could serve as an electrophysiological correlate of the behavioral pitch measure. The scalp recorded FFR may provide for a non-invasive analytic tool to evaluate neural encoding of complex sounds in humans.
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http://dx.doi.org/10.1016/j.heares.2010.12.008DOI Listing
May 2011
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