The ERP signature of sound rise time changes

Revealing brain's cognitive process deeply: a study of the consistent EEG patterns of audio-visual perceptual holistic

Introduction

To investigate the brain's cognitive process and perceptual holistic, we have developed a novel method that focuses on the informational attributes of stimuli.

Methods

We recorded EEG signals during visual and auditory perceptual cognition experiments and conducted ERP analyses to observe specific positive and negative components occurring after 400ms during both visual and auditory perceptual processes. These ERP components represent the brain's perceptual holistic processing activities, which we have named Information-Related Potentials (IRPs). We combined IRPs with machine learning methods to decode cognitive processes in the brain.

Results

Our experimental results indicate that IRPs can better characterize information processing, particularly perceptual holism. Additionally, we conducted a brain network analysis and found that visual and auditory perceptual holistic processing share consistent neural pathways.

Discussion

Our efforts not only demonstrate the specificity, significance, and reliability of IRPs but also reveal their great potential for future brain mechanism research and BCI applications.

Waves of Change: Brain Sensitivity to Differential, not Absolute, Stimulus Intensity is Conserved Across Humans and Rats

Living in rapidly changing environments has shaped the mammalian brain toward high sensitivity to abrupt and intense sensory events-often signaling threats or affordances requiring swift reactions. Unsurprisingly, such events elicit a widespread electrocortical response (the vertex potential, VP), likely related to the preparation of appropriate behavioral reactions. Although the VP magnitude is largely determined by stimulus intensity, the relative contribution of the differential and absolute components of intensity remains unknown. Here, we dissociated the effects of these two components. We systematically varied the size of abrupt intensity increases embedded within continuous stimulation at different absolute intensities, while recording brain activity in humans (with scalp electroencephalography) and rats (with epidural electrocorticography). We obtained three main results. 1) VP magnitude largely depends on differential, and not absolute, stimulus intensity. This result held true, 2) for both auditory and somatosensory stimuli, indicating that sensitivity to differential intensity is supramodal, and 3) in both humans and rats, suggesting that sensitivity to abrupt intensity differentials is phylogenetically well-conserved. Altogether, the current results show that these large electrocortical responses are most sensitive to the detection of sensory changes that more likely signal the sudden appearance of novel objects or events in the environment.

Impaired neural response to speech edges in dyslexia

Speech comprehension has been proposed to critically rely on oscillatory cortical tracking, that is, phase alignment of neural oscillations to the slow temporal modulations (envelope) of speech. Speech-brain entrainment is readjusted over time as transient events (edges) in speech lead to speech-brain phase realignment. Auditory behavioral research suggests that phonological deficits in dyslexia are linked to difficulty in discriminating speech edges. Importantly, research to date has not specifically examined neural responses to speech edges in dyslexia. In the present study, we used MEG to record brain activity from normal and dyslexic readers while they listened to speech. We computed phase locking values (PLVs) to evaluate phase entrainment between neural oscillations and the speech envelope time-locked to edge onsets. In both groups, we observed that edge onsets induced phase resets in the auditory oscillations tracking speech, thereby enhancing their entrainment to speech. Importantly, dyslexic readers showed weaker PLVs compared to normal readers in left auditory regions from ~.15 sec to ~.65 sec after edge onset. Our results indicate that the neural mechanism that adapts cortical entrainment to the speech envelope is impaired in dyslexia. These findings here are consistent with the temporal sampling theory of developmental dyslexia.

Event timing in human vision: Modulating factors and independent functions

Essential for successful interaction with the environment is the human capacity to resolve events in time. Typical event timing paradigms are judgements of simultaneity (SJ) and of temporal order (TOJ). It remains unclear whether SJ and TOJ are based on the same underlying mechanism and whether there are fixed thresholds for resolution. The current study employed four visual event timing task versions: horizontal and vertical SJ and TOJ. Binary responses were analysed using multilevel binary regression modelling. Modulatory effects of potential explanatory variables on event timing perception were investigated: (1) Individual factors (sex and age), (2) temporal factors (SOA, trial number, order of experiment, order of stimuli orientation, time of day) and (3) spatial factors (left or right stimulus first, top or bottom stimulus first, horizontal vs. vertical orientation). The current study directly compares for the first time, performance on SJ and TOJ tasks using the same paradigm and presents evidence that a variety of factors and their interactions selectively modulate event timing functions in humans, explaining the variance found in previous studies. We conclude that SJ and TOJ are partially independent functions, because they are modulated differently by individual and contextual variables.

Effects of formant proximity and stimulus prototypicality on the neural discrimination of vowels: Evidence from the auditory frequency-following response

Cross-language speech perception experiments indicate that for many vowel contrasts, discrimination is easier when the same pair of vowels is presented in one direction compared to the reverse direction. According to one account, these directional asymmetries reflect a universal bias favoring "focal" vowels (i.e., vowels with prominent spectral peaks formed by the convergence of adjacent formants). An alternative account is that such effects reflect an experience-dependent bias favoring prototypical exemplars of native-language vowel categories. Here, we tested the predictions of these accounts by recording the auditory frequency-following response in English-speaking listeners to two synthetic variants of the vowel /u/ that differed in the proximity of their first and second formants and prototypicality, with stimuli arranged in oddball and reversed-oddball blocks. Participants showed evidence of neural discrimination when the more-focal/less-prototypic /u/ served as the deviant stimulus, but not when the less-focal/more-prototypic /u/ served as the deviant, consistent with the focalization account.

Cognitive basis of individual differences in speech perception, production and representations: The role of domain general attentional switching

This study investigated whether individual differences in cognitive functions, attentional abilities in particular, were associated with individual differences in the quality of phonological representations, resulting in variability in speech perception and production. To do so, we took advantage of a tone merging phenomenon in Cantonese, and identified three groups of typically developed speakers who could differentiate the two rising tones (high and low rising) in both perception and production [+Per+Pro], only in perception [+Per-Pro], or in neither modalities [-Per-Pro]. Perception and production were reflected, respectively, by discrimination sensitivity d' and acoustic measures of pitch offset and rise time differences. Components of event-related potential (ERP)-the mismatch negativity (MMN) and the ERPs to amplitude rise time-were taken to reflect the representations of the acoustic cues of tones. Components of attention and working memory in the auditory and visual modalities were assessed with published test batteries. The results show that individual differences in both perception and production are linked to how listeners encode and represent the acoustic cues (pitch contour and rise time) as reflected by ERPs. The present study has advanced our knowledge from previous work by integrating measures of perception, production, attention, and those reflecting quality of representation, to offer a comprehensive account for the underlying cognitive factors of individual differences in speech processing. Particularly, it is proposed that domain-general attentional switching affects the quality of perceptual representations of the acoustic cues, giving rise to individual differences in perception and production.

Perceptual Temporal Asymmetry Associated with Distinct ON and OFF Responses to Time-Varying Sounds with Rising versus Falling Intensity: A Magnetoencephalography Study

This magnetoencephalography (MEG) study investigated evoked ON and OFF responses to ramped and damped sounds in normal-hearing human adults. Two pairs of stimuli that differed in spectral complexity were used in a passive listening task; each pair contained identical acoustical properties except for the intensity envelope. Behavioral duration judgment was conducted in separate sessions, which replicated the perceptual bias in favour of the ramped sounds and the effect of spectral complexity on perceived duration asymmetry. MEG results showed similar cortical sites for the ON and OFF responses. There was a dominant ON response with stronger phase-locking factor (PLF) in the alpha (8–14 Hz) and theta (4–8 Hz) bands for the damped sounds. In contrast, the OFF response for sounds with rising intensity was associated with stronger PLF in the gamma band (30–70 Hz). Exploratory correlation analysis showed that the OFF response in the left auditory cortex was a good predictor of the perceived temporal asymmetry for the spectrally simpler pair. The results indicate distinct asymmetry in ON and OFF responses and neural oscillation patterns associated with the dynamic intensity changes, which provides important preliminary data for future studies to examine how the auditory system develops such an asymmetry as a function of age and learning experience and whether the absence of asymmetry or abnormal ON and OFF responses can be taken as a biomarker for certain neurological conditions associated with auditory processing deficits.

The phonetic landscape in infant consonant perception is an uneven terrain

Previous research revealing universal biases in infant vowel perception forms the basis of the Natural Referent Vowel (NRV) framework (Polka & Bohn, 2011). To explore the feasibility of extending this framework to consonant manner perception, we investigated perception of the stop vs. fricative consonant contrast /b/-/v/ to test the hypothesis that young infants will display a perceptual bias grounded in the acoustic-phonetic properties of these sounds. We examined perception of stop-initial /bas/ and fricative-initial /vas/ syllables in English-learning and French-learning 5- to 6-month-olds. The /b/ and /v/ sounds distinguish words in English and French but have different distributional patterns; in spoken English /b/ occurs more frequently than /v/ whereas in spoken French /v/ occurs more frequently than /b/. A perceptual bias favoring /b/ over /v/ emerged in two experiments. In Experiment 1, a directional asymmetry was observed in discrimination; infants noticed when /vas/ changed to /bas/ but not when /bas/ changed to /vas/. In Experiment 2, a robust listening preference favoring stop-initial /bas/ was evident in responses from the same infants. This is the first study to show a perceptual bias related to consonant manner and to directly measure a consonant perception bias within the same infants. These data encourage further efforts to extend the NRV principles to perception of consonant manner. These findings indicate that we need to reform our view of infant speech perception to accommodate the fact that both discrimination abilities and biases shape speech perception during infancy.

Individual differences in processing pitch contour and rise time in adults: A behavioral and electrophysiological study of Cantonese tone merging

One way to understand the relationship between speech perception and production is to examine cases where the two dissociate. This study investigates the hypothesis that perceptual acuity reflected in event-related potentials (ERPs) to rise time of sound amplitude envelope and pitch contour [reflected in the mismatch negativity (MMN)] may associate with individual differences in production among speakers with otherwise comparable perceptual abilities. To test this hypothesis, advantage was taken of an on-going sound change-tone merging in Cantonese, and compared the ERPs between two groups of typically developed native speakers who could discriminate the high rising and low rising tones with equivalent accuracy but differed in the distinctiveness of their production of these tones. Using a passive oddball paradigm, early positive-going EEG components to rise time and MMN to pitch contour were elicited during perception of the two tones. Significant group differences were found in neural responses to rise time rather than pitch contour. More importantly, individual differences in efficiency of tone discrimination in response latency and magnitude of neural responses to rise time were correlated with acoustic measures of F0 offset and rise time differences in productions of the two rising tones.

Neural processing of amplitude and formant rise time in dyslexia

This study aimed to investigate how children with dyslexia weight amplitude rise time (ART) and formant rise time (FRT) cues in phonetic discrimination. Passive mismatch responses (MMR) were recorded for a/ba/-/wa/contrast in a multiple deviant odd-ball paradigm to identify the neural response to cue weighting in 17 children with dyslexia and 17 age-matched control children. The deviant stimuli had either partial or full ART or FRT cues. The results showed that ART did not generate an MMR in either group, whereas both partial and full FRT cues generated MMR in control children while only full FRT cues generated MMR in children with dyslexia. These findings suggest that children, both controls and those with dyslexia, discriminate speech based on FRT cues and not ART cues. However, control children have greater sensitivity to FRT cues in speech compared to children with dyslexia.

Acoustic landmarks drive delta-theta oscillations to enable speech comprehension by facilitating perceptual parsing

A growing body of research suggests that intrinsic neuronal slow (<10 Hz) oscillations in auditory cortex appear to track incoming speech and other spectro-temporally complex auditory signals. Within this framework, several recent studies have identified critical-band temporal envelopes as the specific acoustic feature being reflected by the phase of these oscillations. However, how this alignment between speech acoustics and neural oscillations might underpin intelligibility is unclear. Here we test the hypothesis that the 'sharpness' of temporal fluctuations in the critical band envelope acts as a temporal cue to speech syllabic rate, driving delta-theta rhythms to track the stimulus and facilitate intelligibility. We interpret our findings as evidence that sharp events in the stimulus cause cortical rhythms to re-align and parse the stimulus into syllable-sized chunks for further decoding. Using magnetoencephalographic recordings, we show that by removing temporal fluctuations that occur at the syllabic rate, envelope-tracking activity is reduced. By artificially reinstating these temporal fluctuations, envelope-tracking activity is regained. These changes in tracking correlate with intelligibility of the stimulus. Together, the results suggest that the sharpness of fluctuations in the stimulus, as reflected in the cochlear output, drive oscillatory activity to track and entrain to the stimulus, at its syllabic rate. This process likely facilitates parsing of the stimulus into meaningful chunks appropriate for subsequent decoding, enhancing perception and intelligibility.

Rise time perception in children with reading and combined reading and language difficulties

Using a non-speech-specific measure of prosody, rise time perception, Goswami and her colleagues have found that individuals with dyslexia perform significantly worse than nonimpaired readers. Studies have also found that children and adults with specific language impairment were impaired on these tasks. Despite the high comorbidity of these disorders, only one study has assessed rise time sensitivity in children with comorbid reading and oral language difficulties. The authors further examined rise time sensitivity in children with both reading and oral language difficulties. They compared performance on rise time perception tasks between 18 children with reading difficulties, 15 children with combined reading and oral language difficulties, and 17 chronological age-matched controls. The authors found a significant interaction between group and performance on auditory tasks. Further tests revealed that chronological age-matched controls were significantly better on the rise time measures compared to both groups of children with reading difficulties. Performance between the groups of children with reading difficulties did not significantly differ.

'I love Rock 'n' Roll'--music genre preference modulates brain responses to music

The present study examined the effect of participants' music genre preference on the neural processes underlying evaluative and cognitive judgements of music using the event-related potential technique. To this aim, two participant groups differing in their preference for Latin American and Heavy Metal music performed a liking judgement and a genre classification task on a variety of excerpts of either music genre. A late positive potential (LPP) was elicited in all conditions between 600 and 900 ms after stimulus onset. During the genre classification task, an early negativity was elicited by the preferred compared to the non-preferred music at around 230-370 ms whereas the non-preferred genre was characterized by a larger LPP. The findings suggest that evaluative and cognitive judgements of music are accompanied by affective responses and that the valence of music may spontaneously modulate early processes of music categorization even when no overt liking judgement is required.

The effect of stimulus choice on cortical auditory evoked potentials (CAEP): consideration of speech segment positioning within naturally produced speech

OBJECTIVE

Cortical auditory evoked potentials (CAEPs) can be elicited to stimuli generated from different parts of speech. The aim of this study was to compare the phoneme /ʃ/ from word medial and word initial positions and its influence on the CAEP.

DESIGN

Stimuli from word medial positions were found to have shorter rise times compared to the same phonemes from word initial positions. A repeated measures design was carried out with CAEPs elicited using /ʃ/ from a word initial and a word medial position.

STUDY SAMPLE

Sixteen individuals with audiometric thresholds within normal limits participated in the study.

RESULTS

Stimuli /ʃ/ from a word medial position elicited CAEPs with significantly larger amplitudes and shorter latencies compared to /ʃ/ from a word initial position (p < 0.05).

CONCLUSIONS

Findings from this study, incorporating naturally produced speech sounds, suggest the need to consider spectral and temporal variations when choosing stimuli to optimize the amplitude and latency characteristics of the CAEP. Overall, findings illustrate good test-retest reliability of CAEP measures using speech stimuli with clinical equipment.

Auditory long latency responses to tonal and speech stimuli

PURPOSE

The effects of type of stimuli (i.e., nonspeech vs. speech), speech (i.e., natural vs. synthetic), gender of speaker and listener, speaker (i.e., self vs. other), and frequency alteration in self-produced speech on the late auditory cortical evoked potential were examined.

METHOD

Young adult men (n = 15) and women (n = 15), all with normal hearing, participated. P1-N1-P2 components were evoked with the following stimuli: 723-Hz tone bursts; naturally produced male and female /a/ tokens; synthetic male and female /a/ tokens; an /a/ token self-produced by each participant; and the same /a/ token produced by the participant but with a shift in frequency.

RESULTS

In general, P1-N1-P2 component latencies were significantly shorter when evoked with the tonal stimulus versus speech stimuli and natural versus synthetic speech (p < .05). Women had significantly shorter latencies for only the P2 component (p < .05). For the tonal versus speech stimuli, P1 amplitudes were significantly smaller, and N1 and P2 amplitudes were significantly larger (p < .05). There was no significant effect of gender on the P1, N1, or P2 amplitude (p > .05).

CONCLUSION

These findings are consistent with the notion that spectrotemporal characteristics of nonspeech and speech stimuli affect P1-N1-P2 latency and amplitude components.

Hearing aid processing changes tone burst onset: effect on cortical auditory evoked potentials in individuals with normal audiometric thresholds

PURPOSE

The validity of using the cortical auditory evoked potential (CAEP) as an objective measure of hearing aid outcome has been questioned in the literature due to stimulus modifications caused by hearing aid processing. This study aimed to investigate the effects of hearing aid processing on the CAEP elicited with tone bursts that may have altered onsets.

METHOD

CAEPs to unprocessed and hearing aid-processed tone bursts were obtained from 16 individuals with normal audiometric thresholds when the onset time, level, and signal-to-noise ratio (SNR) were matched between the 2 conditions. Tone bursts processed by the hearing aid were recorded in an anechoic box and were presented through insert receivers. Unprocessed tone bursts were superimposed with hearing aid noise floor to match the SNR of the hearing aid-processed tone bursts.

RESULTS

Shortening of rise time and overshoot at the onset of the tone burst were evident in the hearing aid-processed stimuli. Statistical analysis of data showed no significant effects of hearing aid processing on the latency or amplitude of CAEP peaks (p > .05).

CONCLUSION

The changes in rise time occurring in the tone bursts due to hearing aid processing may not confound CAEP measures that are used to validate hearing aid fitting.

Language-universal Sensory Deficits in Developmental Dyslexia: English, Spanish, and Chinese

Studies in sensory neuroscience reveal the critical importance of accurate sensory perception for cognitive development. There is considerable debate concerning the possible sensory correlates of phonological processing, the primary cognitive risk factor for developmental dyslexia. Across languages, children with dyslexia have a specific difficulty with the neural representation of the phonological structure of speech. The identification of a robust sensory marker of phonological difficulties would enable early identification of risk for developmental dyslexia and early targeted intervention. Here, we explore whether phonological processing difficulties are associated with difficulties in processing acoustic cues to speech rhythm. Speech rhythm is used across languages by infants to segment the speech stream into words and syllables. Early difficulties in perceiving auditory sensory cues to speech rhythm and prosody could lead developmentally to impairments in phonology. We compared matched samples of children with and without dyslexia, learning three very different spoken and written languages, English, Spanish, and Chinese. The key sensory cue measured was rate of onset of the amplitude envelope (rise time), known to be critical for the rhythmic timing of speech. Despite phonological and orthographic differences, for each language, rise time sensitivity was a significant predictor of phonological awareness, and rise time was the only consistent predictor of reading acquisition. The data support a language-universal theory of the neural basis of developmental dyslexia on the basis of rhythmic perception and syllable segmentation. They also suggest that novel remediation strategies on the basis of rhythm and music may offer benefits for phonological and linguistic development.