Hierarchical amplitude modulation structures and rhythm patterns: Comparing Western musical genres, song, and nature sounds to Babytalk.

Statistical learning of physical stimulus characteristics is important for the development of cognitive systems like language and music. Rhythm patterns are a core component of both systems, and rhythm is key to language acquisition by infants. Accordingly, the physical stimulus characteristics that yield speech rhythm in "Babytalk" may also describe the hierarchical rhythmic relationships that characterize human music and song. Computational modelling of the amplitude envelope of "Babytalk" (infant-directed speech, IDS) using a demodulation approach (Spectral-Amplitude Modulation Phase Hierarchy model, S-AMPH) can describe these characteristics. S-AMPH modelling of Babytalk has shown previously that bands of amplitude modulations (AMs) at different temporal rates and their phase relations help to create its structured inherent rhythms. Additionally, S-AMPH modelling of children's nursery rhymes shows that different rhythm patterns (trochaic, iambic, dactylic) depend on the phase relations between AM bands centred on ~2 Hz and ~5 Hz. The importance of these AM phase relations was confirmed via a second demodulation approach (PAD, Probabilistic Amplitude Demodulation). Here we apply both S-AMPH and PAD to demodulate the amplitude envelopes of Western musical genres and songs. Quasi-rhythmic and non-human sounds found in nature (birdsong, rain, wind) were utilized for control analyses. We expected that the physical stimulus characteristics in human music and song from an AM perspective would match those of IDS. Given prior speech-based analyses, we also expected that AM cycles derived from the modelling may identify musical units like crotchets, quavers and demi-quavers. Both models revealed an hierarchically-nested AM modulation structure for music and song, but not nature sounds. This AM modulation structure for music and song matched IDS. Both models also generated systematic AM cycles yielding musical units like crotchets and quavers. Both music and language are created by humans and shaped by culture. Acoustic rhythm in IDS and music appears to depend on many of the same physical characteristics, facilitating learning.

Neural detection of changes in amplitude rise time in infancy.

Amplitude rise times play a crucial role in the perception of rhythm in speech, and reduced perceptual sensitivity to differences in rise time is related to developmental language difficulties. Amplitude rise times also play a mechanistic role in neural entrainment to the speech amplitude envelope. Using an ERP paradigm, here we examined for the first time whether infants at the ages of seven and eleven months exhibit an auditory mismatch response to changes in the rise times of simple repeating auditory stimuli. We found that infants exhibited a mismatch response (MMR) to all of the oddball rise times used for the study. The MMR was more positive at seven than eleven months of age. At eleven months, there was a shift to a mismatch negativity (MMN) that was more pronounced over left fronto-central electrodes. The MMR over right fronto-central electrodes was sensitive to the size of the difference in rise time. The results indicate that neural processing of changes in rise time is present at seven months, supporting the possibility that early speech processing is facilitated by neural sensitivity to these important acoustic cues.

Delta- and theta-band cortical tracking and phase-amplitude coupling to sung speech by infants.

The amplitude envelope of speech carries crucial low-frequency acoustic information that assists linguistic decoding at multiple time scales. Neurophysiological signals are known to track the amplitude envelope of adult-directed speech (ADS), particularly in the theta-band. Acoustic analysis of infant-directed speech (IDS) has revealed significantly greater modulation energy than ADS in an amplitude-modulation (AM) band centred on ∼2 Hz. Accordingly, cortical tracking of IDS by delta-band neural signals may be key to language acquisition. Speech also contains acoustic information within its higher-frequency bands (beta, gamma). Adult EEG and MEG studies reveal an oscillatory hierarchy, whereby low-frequency (delta, theta) neural phase dynamics temporally organize the amplitude of high-frequency signals (phase amplitude coupling, PAC). Whilst consensus is growing around the role of PAC in the matured adult brain, its role in the development of speech processing is unexplored. Here, we examined the presence and maturation of low-frequency (<12 Hz) cortical speech tracking in infants by recording EEG longitudinally from 60 participants when aged 4-, 7- and 11- months as they listened to nursery rhymes. After establishing stimulus-related neural signals in delta and theta, cortical tracking at each age was assessed in the delta, theta and alpha [control] bands using a multivariate temporal response function (mTRF) method. Delta-beta, delta-gamma, theta-beta and theta-gamma phase-amplitude coupling (PAC) was also assessed. Significant delta and theta but not alpha tracking was found. Significant PAC was present at all ages, with both delta and theta -driven coupling observed.

Difficulties in auditory organization as a cause of reading backwardness? An auditory neuroscience perspective.

Over 30 years ago, it was suggested that difficulties in the 'auditory organization' of word forms in the mental lexicon might cause reading difficulties. It was proposed that children used parameters such as rhyme and alliteration to organize word forms in the mental lexicon by acoustic similarity, and that such organization was impaired in developmental dyslexia. This literature was based on an 'oddity' measure of children's sensitivity to rhyme (e.g. wood, book, good) and alliteration (e.g. sun, sock, rag). The 'oddity' task revealed that children with dyslexia were significantly poorer at identifying the 'odd word out' than younger children without reading difficulties. Here we apply a novel modelling approach drawn from auditory neuroscience to study the possible sensory basis of the auditory organization of rhyming and non-rhyming words by children. We utilize a novel Spectral-Amplitude Modulation Phase Hierarchy (S-AMPH) approach to analysing the spectro-temporal structure of rhyming and non-rhyming words, aiming to illuminate the potential acoustic cues used by children as a basis for phonological organization. The S-AMPH model assumes that speech encoding depends on neuronal oscillatory entrainment to the amplitude modulation (AM) hierarchy in speech. Our results suggest that phonological similarity between rhyming words in the oddity task depends crucially on slow (delta band) modulations in the speech envelope. Contrary to linguistic assumptions, therefore, auditory organization by children may not depend on phonemic information for this task. Linguistically, it is assumed that 'book' does not rhyme with 'wood' and 'good' because the final phoneme differs. However, our auditory analysis suggests that the acoustic cues to this phonological dissimilarity depend primarily on the slower amplitude modulations in the speech envelope, thought to carry prosodic information. Therefore, the oddity task may help in detecting reading difficulties because phonological similarity judgements about rhyme reflect sensitivity to slow amplitude modulation patterns. Slower amplitude modulations are known to be detected less efficiently by children with dyslexia.

A role for amplitude modulation phase relationships in speech rhythm perception.

Prosodic rhythm in speech [the alternation of "Strong" (S) and "weak" (w) syllables] is cued, among others, by slow rates of amplitude modulation (AM) within the speech envelope. However, it is unclear exactly which envelope modulation rates and statistics are the most important for the rhythm percept. Here, the hypothesis that the phase relationship between "Stress" rate (∼2 Hz) and "Syllable" rate (∼4 Hz) AMs provides a perceptual cue for speech rhythm is tested. In a rhythm judgment task, adult listeners identified AM tone-vocoded nursery rhyme sentences that carried either trochaic (S-w) or iambic patterning (w-S). Manipulation of listeners' rhythm perception was attempted by parametrically phase-shifting the Stress AM and Syllable AM in the vocoder. It was expected that a 1π radian phase-shift (half a cycle) would reverse the perceived rhythm pattern (i.e., trochaic → iambic) whereas a 2π radian shift (full cycle) would retain the perceived rhythm pattern (i.e., trochaic → trochaic). The results confirmed these predictions. Listeners judgments of rhythm systematically followed Stress-Syllable AM phase-shifts, but were unaffected by phase-shifts between the Syllable AM and the Sub-beat AM (∼14 Hz) in a control condition. It is concluded that the Stress-Syllable AM phase relationship is an envelope-based modulation statistic that supports speech rhythm perception.

Perception of patterns of musical beat distribution in phonological developmental dyslexia: significant longitudinal relations with word reading and reading comprehension.

INTRODUCTION: In a recent study, we reported that the accurate perception of beat structure in music ('perception of musical meter') accounted for over 40% of the variance in single word reading in children with and without dyslexia (Huss et al., 2011). Performance in the musical task was most strongly associated with the auditory processing of rise time, even though beat structure was varied by manipulating the duration of the musical notes. METHODS: Here we administered the same musical task a year later to 88 children with and without dyslexia, and used new auditory processing measures to provide a more comprehensive picture of the auditory correlates of the beat structure task. We also measured reading comprehension and nonword reading in addition to single word reading. RESULTS: One year later, the children with dyslexia performed more poorly in the musical task than younger children reading at the same level, indicating a severe perceptual deficit for musical beat patterns. They now also had significantly poorer perception of sound rise time than younger children. Longitudinal analyses showed that the musical beat structure task was a significant longitudinal predictor of development in reading, accounting for over half of the variance in reading comprehension along with a linguistic measure of phonological awareness. CONCLUSIONS: The non-linguistic musical beat structure task is an important independent longitudinal and concurrent predictor of variance in reading attainment by children. The different longitudinal versus concurrent associations between musical beat perception and auditory processing suggest that individual differences in the perception of rhythmic timing are an important shared neural basis for individual differences in children in linguistic and musical processing.

N1, P2 and T-complex of the auditory brain event-related potentials to tones with varying rise times in adults with and without dyslexia.

Dyslexia is a learning difficulty affecting the acquisition of fluent reading and spelling skills due to poor phonological processing. Underlying deficits in processing sound rise time have also been found in children and adults with dyslexia. However, the neural basis for these deficits is unknown. In the present study event-related potentials were used to index neural processing and examine the effect of rise time manipulation on the obligatory N1, T-complex and P2 responses in English speaking adults with and without dyslexia. The Tb wave of the T-complex showed differences between groups, with the amplitudes for Tb becoming less negative with increased rise time for the participants with dyslexia only. Frontocentral N1 and P2 did not show group effects. Enhanced Tb amplitude that is modulated by rise time could indicate altered neural networks at the lateral surface of the superior temporal gyrus in adults with dyslexia.

Music, rhythm, rise time perception and developmental dyslexia: perception of musical meter predicts reading and phonology.

INTRODUCTION: Rhythm organises musical events into patterns and forms, and rhythm perception in music is usually studied by using metrical tasks. Metrical structure also plays an organisational function in the phonology of language, via speech prosody, and there is evidence for rhythmic perceptual difficulties in developmental dyslexia. Here we investigate the hypothesis that the accurate perception of musical metrical structure is related to basic auditory perception of rise time, and also to phonological and literacy development in children. METHODS: A battery of behavioural tasks was devised to explore relations between musical metrical perception, auditory perception of amplitude envelope structure, phonological awareness (PA) and reading in a sample of 64 typically-developing children and children with developmental dyslexia. RESULTS: We show that individual differences in the perception of amplitude envelope rise time are linked to musical metrical sensitivity, and that musical metrical sensitivity predicts PA and reading development, accounting for over 60% of variance in reading along with age and I.Q. Even the simplest metrical task, based on a duple metrical structure, was performed significantly more poorly by the children with dyslexia. CONCLUSIONS: The accurate perception of metrical structure may be critical for phonological development and consequently for the development of literacy. Difficulties in metrical processing are associated with basic auditory rise time processing difficulties, suggesting a primary sensory impairment in developmental dyslexia in tracking the lower-frequency modulations in the speech envelope.

The ERP signature of sound rise time changes.

Sounds, whether speech or non-speech, vary in how rapidly their peak amplitudes are reached. The time taken for sounds to reach their maximum amplitude is known as the rise time and this variable is an important perceptual cue for representation of the sound amplitude envelope. In the experiments described here healthy adult volunteers passively listened to tones varying in rise time. An oddball design was used and both N1 and MMN components were examined. Experiment 1 contrasted tone stimuli of 15 ms vs. 185 ms rise time. The shorter 15 ms rise time stimuli elicited an N1b over central frontal electrodes of significantly greater amplitude than the 185 ms rise time stimuli. MMN was also observable for both the 15 ms and 185 ms rise time tones when the same stimuli served as deviant vs. standard. Experiment 2 explored the possible confound of rise time and overall stimulus intensity change (tones with shorter rise times sound louder). New stimuli were created in which overall stimulus intensity between short and long rise times was perceptually matched. N1b amplitude differences to the contrastive rise times were still observed, suggesting that N1b may reflect an auditory cortex detector mechanism sensitive to changes in rise time, relatively independently of sound intensity changes. These findings are discussed with reference to their implications for speech perception processes.

Rhythmic motor entrainment in children with speech and language impairments: tapping to the beat.

In prior work (Corriveau et al., 2007), we showed that children with speech and language impairments (SLI) were significantly less sensitive than controls to two auditory cues to rhythmic timing, amplitude envelope rise time and duration. Here we explore whether rhythmic problems extend to rhythmic motor entrainment. Tapping in synchrony with a beat has been described as the simplest rhythmic act that humans perform. We explored whether tapping to a beat would be impaired in children for whom auditory rhythmic timing is impaired. Children with SLI were indeed found to be impaired in a range of measures of paced rhythmic tapping, but were not equally impaired in tapping in an unpaced control condition requiring an internally-generated rhythm. The severity of impairment in paced tapping was linked to language and literacy outcomes.

Rhythmic processing in children with developmental dyslexia: auditory and motor rhythms link to reading and spelling.

Potential links between the language and motor systems in the brain have long attracted the interest of developmental psychologists. In this paper, we investigate a link often observed (e.g., [Wolff, P.H., 2002. Timing precision and rhythm in developmental dyslexia. Reading and Writing, 15 (1), 179-206.] between motor tapping and written language skills. We measure rhythmic finger tapping (paced by a metronome beat versus unpaced) and motor dexterity, phonological and auditory processing in 10-year old children, some of whom had a diagnosis of developmental dyslexia. We report links between paced motor tapping, auditory rhythmic processing and written language development. Motor dexterity does not explain these relationships. In regression analyses, paced finger tapping explained unique variance in reading and spelling. An interpretation based on the importance of rhythmic timing for both motor skills and language development is proposed.

DNA damage in male gonad cells of Green mussel (Perna viridis) upon exposure to tobacco products.

DNA damage (determined by the Comet Assay) and the occurrence of deformed nuclei were measured as endpoints of genotoxicity in male gonad cells of the marine mussel (Perna viridis). Upon exposure of the organism to varying concentrations of extracts of smoked and non-smoked cigar tobacco over a period of 16 days, DNA damage was found to be highest in marine mussels exposed to extracts of smoked cigar tobacco. Conversely, more deformed nuclei were detected in marine mussels exposed to extracts of non-smoked cigar tobacco. The level of DNA damage and the number of deformed nuclei reach a maximum at day 12 of exposure to both extracts but decrease thereafter. This phenomenon is attributed to the organism's capacity to maintain the integrity of its genetic material upon exposure to potential genotoxicants present in the tobacco extracts. A dose response in DNA damage and deformed nuclei was also detected in isolated gonad cells upon in vitro exposure to hydrogen peroxide a known DNA strand breaking agent. The results of this study indicate that the DNA in male gonad cells of the marine mussel is damaged upon exposure to genotoxicants, and suggests the suitability of the organism for future investigations into the effect of such agents on its reproductive capacities.