Tone Pairs Research Articles

Auditory gating in adults with dyslexia: An ERP account of diminished rapid neural adaptation

ObjectiveA recent functional magnetic resonance imaging (fMRI) study of adults with dyslexia showed a general deficit in suppressing responses to various types of repetitive stimuli. This diminished neural adaptation may interfere with implicit learning and forming stable word representations. With fMRI, spatial but not temporal characteristics of the adaptation response could be identified. We address this knowledge gap using event-related potentials. MethodsFourteen adults with dyslexia and 14 controls participated in an auditory gating paradigm using tone pairs. Response amplitudes and latencies for N1 and P2 were measured. Participants also compared word pairs consisting of identical or subtly different words, a task requiring stable word representations. ResultsOnly the controls showed a robust gating effect in an attenuated N1 response to the second tone relative to the first. The dyslexia group was less accurate than the controls in detecting word differences. The N1 gating magnitude was associated with this detection accuracy. ConclusionsNeural adaptation occurs by approximately 100 ms after stimulus presentation and is diminished in adults with dyslexia. This complements fMRI findings of relevant brain regions by implying a time window representing sensory and pre-attentive auditory processes. SignificanceThe association between gating magnitude and word discrimination contributes to a neurophysiological account of underspecified word representations.

A parsimonious approach for screening moderate-to-profound hearing loss in a community-dwelling geriatric population based on a decision tree analysis

BackgroundHearing loss is one of the most common modifiable factors associated with cognitive and functional decline in geriatric populations. An accurate, easy-to-apply, and inexpensive hearing screening method is needed to detect hearing loss in community-dwelling elderly people, intervene early and reduce the negative consequences and burden of untreated hearing loss on individuals, families and society. However, available hearing screening tools do not adequately meet the need for large-scale geriatric hearing detection due to several barriers, including time, personnel training and equipment costs. This study aimed to propose an efficient method that could potentially satisfy this need.MethodsIn total, 1793 participants (≥60 years) were recruited to undertake a standard audiometric air conduction pure tone test at 4 frequencies (0.5–4 kHz). Audiometric data from one community were used to train the decision tree model and generate a pure tone screening rule to classify people with or without moderate or more serious hearing impairment. Audiometric data from another community were used to validate the tree model.ResultsIn the decision tree analysis, 2 kHz and 0.5 kHz were found to be the most important frequencies for hearing severity classification. The tree model suggested a simple two-step screening procedure in which a 42 dB HL tone at 2 kHz is presented first, followed by a 47 dB HL tone at 0.5 kHz, depending on the individual’s response to the first tone. This approach achieved an accuracy of 91.20% (91.92%), a sensitivity of 95.35% (93.50%) and a specificity of 86.85% (90.56%) in the training dataset (testing dataset).ConclusionsA simple two-step screening procedure using the two tones (2 kHz and 0.5 kHz) selected by the decision tree analysis can be applied to screen moderate-to-profound hearing loss in a community-based geriatric population in Shanghai. The decision tree analysis is useful in determining the optimal hearing screening criteria for local elderly populations. Implanting the pair of tones into a well-calibrated sound generator may create a simple, practical and time-efficient screening tool with high accuracy that is readily available at healthcare centers of all levels, thereby facilitating the initiation of extensive nationwide hearing screening in older adults.

Neural Encoding of Pitch Direction Is Enhanced in Musically Trained Children and Is Related to Reading Skills.

Musical training in childhood has been linked to enhanced sound encoding at different stages of the auditory processing. In the current study, we used auditory event-related potentials to investigate cortical sound processing in 9- to 15-year-old children (N = 88) with and without musical training. Specifically, we recorded the mismatch negativity (MMN) and P3a responses in an oddball paradigm consisting of standard tone pairs with ascending pitch and deviant tone pairs with descending pitch. A subsample of the children (N = 44) also completed a standardized test of reading ability. The musically trained children showed a larger P3a response to the deviant sound pairs. Furthermore, the amplitude of the P3a correlated with a pseudo-word reading test score. These results corroborate previous findings on enhanced sound encoding in musically trained children and are in line with studies suggesting that neural discrimination of spectrotemporal sound patterns is predictive of reading ability.

Predictable tones elicit stimulus-specific suppression of evoked activity in auditory cortex

The auditory cortex is sensitive to many forms of acoustic regularity, resulting in suppressed neural activity for expected auditory events. It is unclear whether this activity reduction for expected events is the result of suppression of neurons that are tuned to the expected stimulus (i.e., dampening), or alternatively suppression of neurons that are tuned away from the expected stimulus (i.e., sharpening). In the present study, we adjudicated between these models by characterizing the effect of expectation on the ability to classify the identity of auditory stimuli from auditory neural activity patterns, using magnetoencephalography (MEG) in healthy human observers. Participants listened to pure tone pairs, in which the identity of the second tone was either expected or unexpected. The task of the participants was to detect a target tone, which deviated strongly from both the expected and unexpected tones. We found a strong suppression of the overall neural response in the expected condition compared to the unexpected condition. Linear classifiers showed a reduced ability to decode stimulus identity from event-related auditory fields in the expected condition compared to the unexpected condition. This suggests that stimulus-specific event-related activity is dampened for expected tones in auditory cortex.

Pairing vagus nerve stimulation with tones drives plasticity across the auditory pathway.

Previous studies have demonstrated that pairing vagus nerve stimulation (VNS) with sounds can enhance the primary auditory cortex (A1) response to the paired sound. The neural response to sounds following VNS-sound pairing in other subcortical and cortical auditory fields has not been documented. We predicted that VNS-tone pairing would increase neural responses to the paired tone frequency across the auditory pathway. In this study, we paired VNS with the presentation of a 9-kHz tone 300 times a day for 20 days. We recorded neural responses to tones from 2,950 sites in the inferior colliculus (IC), A1, anterior auditory field (AAF), and posterior auditory field (PAF) 24 h after the last pairing session in anesthetized rats. We found that VNS-tone pairing increased the percentage of IC, A1, AAF, and PAF that responds to the paired tone frequency. Across all tested auditory fields, the response strength to tones was strengthened in VNS-tone paired rats compared with control rats. VNS-tone pairing reduced spontaneous activity, frequency selectivity, and response threshold across the auditory pathway. This is the first study to document both cortical and subcortical plasticity following VNS-sound pairing. Our findings suggest that VNS paired with sound presentation is an effective method to enhance auditory processing.NEW & NOTEWORTHY Previous studies have reported primary auditory cortex plasticity following vagus nerve stimulation (VNS) paired with a sound. This study extends previous findings by documenting that fields across the auditory pathway are altered by VNS-tone pairing. VNS-tone pairing increases the percentage of each field that responds to the paired tone frequency. This is the first study to document both cortical and subcortical plasticity following VNS-sound pairing.

Are Asian Language Speakers Similar or Different? The Perception of Mandarin Lexical Tones by Naïve Listeners from Tonal Language Backgrounds: A Preliminary Comparison of Thai and Vietnamese Listeners

Mandarin is one of the most representative tonal languages in the world with four tone categories (Tone 1 (T1): high level (ā); Tone 2 (T2): high rising (á); Tone 3 (T3): dipping (ǎ); Tone 4 (T4): high falling (à)). Learning Mandarin tones is known to be difficult for speakers from diverse linguistic backgrounds. The perception of Mandarin tones by naïve, non-native listeners from two tonal languages with a larger tone inventory than Mandarin—Thai and Vietnamese—was examined. The listeners’ discrimination accuracy of six tone pairs (T1–T2, T1–T3, T1–T4, T2–T3, T2–T4, T3–T4) was assessed and compared to that of native speakers of Mandarin on the one hand and Australian English on the other hand. The Thai and Vietnamese groups were clearly less accurate than the Mandarin group and showed a different pattern of results from each other. The Australian English group was less accurate than the Thai group only for T2–T4 and did not differ from the Vietnamese group for any of the pairs. Taken together, these findings suggest that first language tone knowledge may not necessarily be facilitative and that lack of experience with lexical tones may not disadvantage listeners from non-tonal language backgrounds in processing unfamiliar tones.

Assessing the Link Between Perception and Production in Cantonese Tone Acquisition

Purpose Previous studies showed early production precedes late perception in Cantonese tone acquisition, contrary to the general principle that perception precedes production in child language. How tone production and perception are linked in 1st language acquisition remains largely unknown. Our study revisited the acquisition of tone in Cantonese-speaking children, exploring the possible link between production and perception in 1st language acquisition. Method One hundred eleven Cantonese-speaking children aged between 2;0 and 6;0 (years;months) and 10 adolescent reference speakers participated in tone production and perception experiments. Production materials with 30 monosyllabic words were transcribed in filtered and unfiltered conditions by 2 native judges. Perception accuracy was based on a 2-alternative forced-choice task with pictures covering all possible tone pair contrasts. Results Children's accuracy of production and perception of all the 6 Cantonese tones was still not adultlike by age 6;0. Both production and perception accuracies matured with age. A weak positive link was found between the 2 accuracies. Mother's native language contributed to children's production accuracy. Conclusions Our findings show that production and perception abilities are associated in tone acquisition. Further study is needed to explore factors affecting production accuracy in children. Supplemental Material https://doi.org/10.23641/asha.7960826.

Modulated stimuli demonstrate asymmetric interactions between hearing and vision

The nature of interactions between the senses is a topic of intense interest in neuroscience, but an unresolved question is how sensory information from hearing and vision are combined when the two senses interact. A problem for testing auditory-visual interactions is devising stimuli and tasks that are equivalent in both modalities. Here we report a novel paradigm in which we first equated the discriminability of the stimuli in each modality, then tested how a distractor in the other modality affected performance. Participants discriminated pairs of amplitude-modulated tones or size-modulated visual objects in the form of a cuboid shape, alone or when a similarly modulated distractor stimulus of the other modality occurred with one of the pair. Discrimination of sound modulation depth was affected by a modulated cuboid only when their modulation rates were the same. In contrast, discrimination of cuboid modulation depth was little affected by an equivalently modulated sound. Our results suggest that what observers perceive when auditory and visual signals interact is not simply determined by the discriminability of the individual sensory inputs, but also by factors that increase the perceptual binding of these inputs, such as temporal synchrony.

Change detection to tone pairs during the first year of life – Predictive longitudinal relationships for EEG-based source and time-frequency measures

Brain responses related to auditory processing show large changes throughout infancy and childhood with some evidence that the two hemispheres might mature at different rates. Differing rates of hemispheric maturation could be linked to the proposed functional specialization of the hemispheres in which the left auditory cortex engages in analysis of precise timing information whereas the right auditory cortex focuses on analysis of sound frequency. Here the auditory change detection process for rapidly presented tone-pairs was examined in a longitudinal sample of infants at the age of 6 and 12 months using EEG. The ERP response related to change detection of a frequency contrast, its estimated source strength in the auditory areas, as well as time-frequency indices showed developmental effects. ERP amplitudes, source strength, spectral power and inter-trial phase locking decreased across age. A differential lateralization pattern emerged between 6 and 12 months as shown by inter-trial phase locking at 2–3 Hz; specifically, a larger developmental change was observed in the right as compared to the left hemisphere. Predictive relationships for the change in source strength from 6 months to 12 months were found. Six-month predictors were source strength and phase locking values at low frequencies. The results show that the infant change detection response in rapidly presented tone pairs is mainly determined by low frequency power and phase-locking with a larger phase-locking response at 6 months predicting greater change at 12 months. The ability of the auditory system to respond systematically across stimuli is suggested as a marker of maturational change that leads to more automatic and fine-tuned cortical responses.

Effect of sound pressure level on contralateral inhibition underlying duration-tuned neurons in the mammalian inferior colliculus.

Duration tuning in the mammalian inferior colliculus (IC) is created by the interaction of excitatory and inhibitory synaptic inputs. We used extracellular recordings and paired tone stimulation to measure the strength and time course of the contralateral inhibition underlying duration-tuned neurons (DTNs) in the IC of the awake bat. The onset time of a short, best duration (BD), excitatory probe tone set to +10 dB (re threshold) was varied relative to the onset of a longer-duration, nonexcitatory (NE) suppressor tone whose sound pressure level (SPL) was varied. Spikes evoked by the roving BD tone were suppressed when the stationary NE tone amplitude was at or above the BD tone threshold. When the NE tone was increased from 0 to +10 dB, the inhibitory latency became shorter than the excitatory first-spike latency and the duration of inhibition increased, but no further changes occurred at +20 dB (re BD tone threshold). We used the effective duration of inhibition as a function of the NE tone amplitude to obtain suppression-level functions that were used to estimate the inhibitory half-maximum SPL (ISPL50). We also measured rate-level functions of DTNs with single BD tones varied in SPL and modeled the excitatory half-maximum SPL (ESPL50). There was a correlation between the ESPL50 and ISPL50, and the dynamic range of excitation and inhibition were similar. We conclude that the strength of inhibition changes in proportion to excitation as a function of SPL, and this feature likely contributes to the amplitude tolerance of the responses of DTNs. NEW & NOTEWORTHY Duration-tuned neurons arise from excitatory and inhibitory synaptic inputs offset in time. We measured the strength and time course of inhibition to changes in sound level. The onset of inhibition shortened while its duration lengthened as the stimulus level increased from 0 to +10 dB re threshold; however, no further changes were observed at +20 dB. Excitatory rate-level and inhibitory suppression-level response functions were strongly correlated, suggesting a mechanism for level tolerance in duration tuning.

Auditory Gating and Extended High-Frequency Thresholds in Normal-Hearing Adults With Minimal Tinnitus.

Purpose The goal of this study was to assess whether peripheral auditory sensitivity in frequency regions above 8 kHz is related to central inhibitory function, as measured through a sensory gating paradigm, in normal-hearing adults with tinnitus (TINN) and without tinnitus (NTINN). The contribution of gating processes and peripheral sensitivity in extended high frequencies to tinnitus severity was evaluated via a hierarchical multiple regression method. Method Cortical auditory evoked potentials (CAEPs) were recorded in response to pairs of tones in normal-hearing adults without tinnitus, NTINN ( n = 45), and adults with tinnitus, TINN ( n = 21). CAEP peak component amplitude, latency, and gating indices were compared and correlated with extended high-frequency (EHF) pure-tone averages (PTAs) across groups and with tinnitus severity. An exploratory analysis was performed to investigate gating variability within the TINN group. Based on Tinnitus Handicap Inventory (Newman, Jacobson, & Spitzer, 1996) median scores, the TINN group was categorized into low- and high-median subgroups, and gating indices were compared between these subgroups. A hierarchical multiple regression analysis was performed to determine the amount of variance accounted for in the TINN group. Results Decreased gating via the CAEP Pa component and increased gating via the N1 component correlated with increased tinnitus severity, even in individuals who would traditionally be classified as having no tinnitus handicap. In the TINN group, lower EHF PTA thresholds correlated with tinnitus severity and decreased Pa gating. Individuals with a greater severity of tinnitus demonstrated atypical gating function reflected in both Pa and N1 components. Gating function and EHF PTA accounted for significant variance regarding tinnitus severity. Conclusions A trade-off between lower and higher level gating function was observed in adults with normal hearing and tinnitus, indicative of higher order compensatory mechanisms. Better cochlear sensitivity in extended high frequencies was related to decreased lower level gating processes and increased tinnitus THI scores, suggestive of an interaction between decreased gating and heightened auditory awareness. We are currently exploring whether gating processes in this population are compensatory, and the role of gating in auditory awareness.

Temporal boundary of auditory event formation: An electrophysiological marker

The formation of auditory events requires integration between successive sounds. There is a temporal limit below which a single sound event is perceived while above which a second perceptual event is formed. Behavioral studies applying the Temporal Order Judgment paradigm showed that this boundary is between 20 and 70 ms. Here we provide event-related potential (ERP) evidence from two experiments showing a qualitative change in the processing of tone pairs between 25 and 75 ms within-pair inter-stimulus intervals (ISI). We also show that this temporal boundary can be influenced by the immediate acoustical context, the statistical distribution of the ISIs within the sequence of tone-pairs.

Vagus Nerve Stimulation Rate and Duration Determine whether Sensory Pairing Produces Neural Plasticity

Repeatedly pairing a brief train of vagus nerve stimulation (VNS) with an auditory stimulus drives reorganization of primary auditory cortex (A1), and the magnitude of this VNS-dependent plasticity is dependent on the stimulation parameters, including intensity and pulse rate. However, there is currently little data to guide the selection of VNS train durations, an easily adjusted parameter that could influence the effect of VNS-based therapies. Here, we tested the effect of varying the duration of the VNS train on the extent of VNS-dependent cortical plasticity. Rats were exposed to a 9 kHz tone 300 times per day for 20 days. Coincident with tone presentation, groups received trains of 4, 16, or 64 pulses of VNS delivered at 30 Hz, corresponding to train durations of 0.125 s, 0.5 s, and 2.0 s, respectively. High-density microelectrode mapping of A1 revealed that 0.5 s duration VNS trains significantly increased the number of neurons in A1 that responded to tones near the paired tone frequency. Trains lasting 0.125 or 2.0 s failed to alter A1 responses, indicating that both shorter and longer stimulation durations are less effective at enhancing plasticity. A second set of experiments evaluating the effect of delivering 4 or 64 pulses in a fixed 0.5 s VNS train duration paired with tone presentation reveal that both slower and faster stimulation rates are less effective at enhancing plasticity. We incorporated these results with previous findings describing the effect of stimulation parameters on VNS-dependent plasticity and activation of neuromodulatory networks to generate a model of synaptic activation by VNS.

Effects of self-reported hearing difficulty on intensity discrimination judgments

Listeners may report difficulty understanding speech, particularly in background noise, despite having normal audiograms that do not suggest a sensorineural hearing loss. One potential cause of this hearing difficulty is auditory neuropathy (AN), a disruption in the function of the auditory nerve. AN may specifically affect auditory nerve fibers that code intensity differences at higher sound levels, resulting in particular difficulty with speech recognition but preserved audiometric thresholds. This study aims to detect AN by measuring intensity discrimination thresholds at different frequencies and sound levels, comparing performance to self-reported measures of hearing difficulty. Listeners performed an intensity discrimination task where they heard pairs of tones and judged whether the first or second tone was louder. Psychophysical functions were computed to measure listeners' discrimination thresholds and point of subjective equality (PSE, i.e., point at which the two tones are judged to have equal intensity). Results showed that listeners who report greater speech-in-noise difficulty had shifted PSEs specifically at higher sound levels (60–70 dB SPL, the range used in conversational speech), such that they were more likely to perceive the second tone as louder than it was. The results suggest that an intensity discrimination task may be a useful test for AN.

Development of tonal discrimination in young heritage speakers of Cantonese

This study uses the Perceptual Assimilation Model for Suprasegmentals (PAM-S) (So & Best, 2008, 2010), supported by the assumptions of the L2 Intonation Learning theory (LILt, Mennen, 2015), to investigate how young heritage speakers of Cantonese living in the United States acquired Cantonese tones. Sixty-seven heritage speakers, aged 5–11, were tested on their perception of Cantonese tonal contrasts using an ABX discrimination task. They were compared to 64 peers aged 5–12 in Hong Kong, where Cantonese is spoken as the majority language but English is also acquired from a young age. Two pairs of tones were tested: Tones 2 (mid rising) and 5 (low rising), which have similar pitch heights and contours, and Tones 1 (high level) and 4 (low falling), which have a larger phonetic contrast. As predicted, the heritage speakers were more accurate in discriminating between the more distinct pair of tones than between the more similar pair. They also scored lower than their peers from Hong Kong in both contrast conditions. Age of testing predicted accuracy for both groups, and Chinese literacy also had a significant effect for the heritage speakers. The potential lack of the Tone 2–5 contrast in the heritage speakers’ input is discussed as an explanation for these findings. This study illustrates the divergence in heritage speakers’ phonological development compared to majority language speakers, and shows the relevance of the PAM-S and LILt to the heritage language context.

Effects of subanesthetic intravenous ketamine infusion on neuroplasticity-related proteins in the prefrontal cortex, amygdala, and hippocampus of Sprague-Dawley rats

Ketamine, a multimodal dissociative anesthetic, is a powerful analgesic administered following trauma due to its hemodynamic and respiratory stability. However, ketamine can cause hallucination and dissociation which may adversely impact traumatic memory after an injury. The effects of ketamine on proteins implicated in neural plasticity are unclear due to different doses, routes, and timing of drug administration in previous studies. Here, we investigated the effects of a single intravenous (IV) ketamine infusion on protein levels in three brain regions of rats. Adult male Sprague-Dawley rats with indwelling IV catheters underwent an auditory fear conditioning (three pairings of tone and mild footshock 0.8 mA, 0.5 s) and received a high dose of IV ketamine (0 or 40 mg/kg/2 h) infusion (Experiment 1). In a follow-up study, animals received a low dose of IV ketamine (0 or 10 mg/kg/2 h) infusion (Experiment 2). Two hours after the infusion, brain tissue from the medial prefrontal cortex (mPFC), hippocampus, and amygdala were collected for western blot analyses. Protein levels of a transcription factor (c-Fos), brain-derived neurotrophic factor (BDNF), and phosphorylated extracellular signal-regulated kinase (pERK) were quantified in these regions. The 40 mg/kg ketamine infusion increased c-Fos levels in the mPFC and amygdala as well as pERK levels in the mPFC and hippocampus. The 10 mg/kg ketamine infusion increased BDNF levels in the amygdala, but decreased pERK levels in the mPFC and hippocampus. These findings suggest that a clinically relevant route of ketamine administration produces dose-dependent and brain region-specific effects on proteins involved in neuroplasticity.

Does phonological rule of tone substitution modulate mismatch negativity?

This study examined whether the phonological substitution rule of tone sandhi modulates tone perception in the preattentive stage. Tone sandhi is commonly present in East Asian languages. An example from Mandarin is the Tone tone 3 sandhi rule: T3 is pronounced as T2 when followed by another T3 (33 → 23). Previous mismatch negativity (MMN) studies in Mandarin have reported a smaller amplitude or longer latency in standard-deviant pair consisting of T2 and T3 (T2-T3) than in T1-T3. The most widely accepted explanation for this is that T2 and T3 have steeper pitch slopes than T1. This study tested an alternative account based on the phonological rule that the frequent substitution that occurs between T2 and T3 results in reduced MMN. In Experiment 1, we first tried to replicate the finding in Mandarin. In Experiment 2, using both unskilled and skilled speakers, we tested a sandhi tone pair of very different pitch slopes in Taiwanese. Delayed peak latency of sandhi pair was evident in both languages but only in skilled speakers. Our results did not support the shared-pitch-slope account and were instead consistent with the argument that a language-specific phonological rule could modulate preattentive tone processing.

“Equiheptatonic” Tuning in Thai Classical Music: Strict Propriety and Step Sizes

Tunings of Thai classical music have been a source of disagreement during the past century. Focusing on 28 ensembles, the present study analyzes ways in which the intervals they produce can be formulated so that they are both falsifiable and verifiable. Of these, a model that corresponds to Rothenberg’s formulation of strict propriety excels among pairs of tones that span different numbers of scale degrees. According to Rothenberg’s model of strict propriety, intervals that span fewer scale degrees are smaller than intervals that span more scale degrees. Further, according to a formulation of clear patterning among intervals that span precisely two scale degrees (i.e., a single step), there is no clear pattern of one-step intervals unless all the instances of at least one interval that spans two particular consecutive scale degrees are smaller and/or larger than all the instances of all the other intervals that span two consecutive scale degrees. Among the 28 ensembles, single-step intervals tend to constitute chains that overlap in size rather than a clear pattern of small and large intervals.

Talker normalization in typical Cantonese-speaking listeners and congenital amusics: Evidence from event-related potentials.

Despite the lack of invariance in the mapping between the acoustic signal and phonological representation, typical listeners are capable of using information of a talker's vocal characteristics to recognize phonemes, a process known as “talker normalization”. The current study investigated the time course of talker normalization in typical listeners and individuals with congenital amusia, a neurodevelopmental disorder of refined pitch processing. We examined the event-related potentials (ERPs) underling lexical tone processing in 24 Cantonese-speaking amusics and 24 typical listeners (controls) in two conditions: blocked-talker and mixed-talker conditions. The results demonstrated that for typical listeners, effects of talker variability can be observed as early as in the N1 time-window (100–150 ms), with the N1 amplitude reduced in the mixed-talker condition. Significant effects were also found in later components: the N2b/c peaked significantly earlier and the P3a and P3b amplitude was enhanced in the blocked-talker condition relative to the mixed-talker condition, especially for the tone pair that is more difficult to discriminate. These results suggest that the blocked-talker mode of stimulus presentation probably facilitates auditory processing and requires less attentional effort with easier speech categorization than the mixed-talker condition, providing neural evidence for the “active control theory”. On the other hand, amusics exhibited comparable N1 amplitude to controls in both conditions, but deviated from controls in later components. They demonstrated overall later N2b/c peak latency significantly reduced P3a amplitude in the blocked-talker condition and reduced P3b amplitude irrespective of talker conditions. These results suggest that the amusic brain was intact in the auditory processing of talker normalization processes, as reflected by the comparable N1 amplitude, but exhibited reduced automatic attentional switch to tone changes in the blocked-talker condition, as captured by the reduced P3a amplitude, which presumably underlies a previously reported perceptual “anchoring” deficit in amusics. Altogether, these findings revealed the time course of talker normalization processes in typical listeners and extended the finding that conscious pitch processing is impaired in the amusic brain.

Effects of Acoustic Paired Associative Stimulation on Late Auditory Evoked Potentials

Paired associative stimulation (PAS), a form of non-invasive cortical stimulation pairing transcranial magnetic stimulation (TMS) with a peripheral sensory stimulus, has been shown to induce neuroplastic effects in the human motor, somatosensory and auditory cortex. The current study investigated the effects of acoustic PAS on late auditory evoked potentials (LAEP) and the influence of tone duration and placebo stimulation. In two experiments, 18 participants underwent a PAS with a 4 kHz paired tone of 400 ms duration using 200 pairs of stimuli (TMS-pulse over the left auditory cortex 45 ms after tone-onset) presented at 0.1 Hz. In Experiment 1 this protocol was contrasted with a protocol using a short paired tone of 23 ms duration (PAS-23 ms vs. PAS-400 ms). In Experiment 2 this PAS protocol was contrasted with sham stimulation (PAS-400 ms-sham vs. PAS-400 ms). Before and after PAS, LAEP were recorded for tones of 4 kHz (same carrier frequency as the paired tone) and 1 kHz as control tone. In Experiment 1, there was a significant difference between LAEP amplitudes of the 4 kHz tone after PAS-23 ms and PAS-400 ms with higher LAEP amplitudes after PAS-23 ms. Before both conditions, no difference could be detected. In Experiment 2 we observed a significant overall decrease in LAEP amplitudes pre to post PAS. Unspecific decreases of LAEP following PAS with a long paired tone (PAS-400 ms) might be related to habituation effects due to repeated presentation of sound stimuli which are not evident for PAS with a short paired tone (PAS-23 ms). Interpreting this result using the concept of temporal integration time allows us to discuss it in the context of spike-timing dependent plasticity.