Nandini C. Singh

Neuroimaging reveals dual routes to reading in simultaneous proficient readers of two orthographies

Orthographic differences across languages impose differential weighting on distinct component processes, and consequently on different pathways during word-reading tasks. Readers of transparent orthographies such as Italian and Hindi are thought to rely on spelling-to-sound assembly and show increased activation in phonologically tuned areas along the dorsal pathway, whereas reading an opaque orthography such as English is thought to rely more on lexically mediated processing associated with increased activation of semantically tuned regions along the ventral pathway. To test if biliterate Hindi/English readers exhibit orthography-specific reading pathways, we used behavioural measures and functional neuroimaging. Reaction times and activation patterns of monolingual English and Hindi readers were compared to two groups of adult biliterates; 14 simultaneous readers who learnt to read both languages at age 5 and 10 sequential readers who learnt Hindi at 5 and English at 10. Simultaneous, but not sequential readers demonstrated relative activation differences of dorsal and ventral areas in the two languages. Similar to native counterparts, simultaneous readers preferentially activated the left inferior temporal gyrus for English and left inferior parietal lobule (L-IPL) for Hindi, whereas, sequential readers showed higher activation along the L-IPL for reading both languages. We suggest that early simultaneous exposure to reading distinct orthographies results in orthography-specific plasticity that persists through adulthood.

Sounds of melody—Pitch patterns of speech in autism

The objective of this study was to find a pattern in vocalizations of children with Autism Spectrum Disorder (ASD). We compared the intonational features of 15 children with ASD who showed speech, aged 4-10 years, with 10 age-matched typically developing controls. Exaggerated pitch, pitch range, pitch excursion and pitch contours were observed in speech of children with autism, but absent in age-matched controls. These exaggerated features, which are distinctive characteristics of motherese, were also seen in interactions of an independent group of 8 mothers of typical infants using child-directed speech. Our findings provide the first evidence of a distinct pattern in vocal output from children with autism. They also demonstrate that speech patterns might follow a delayed developmental trajectory in these children.

Fronto‐Temporal Connectivity is Preserved During Sung but Not Spoken Word Listening, Across the Autism Spectrum

Co‐occurrence of preserved musical function with language and socio‐communicative impairments is a common but understudied feature of Autism Spectrum Disorders (ASD). Given the significant overlap in neural organization of these processes, investigating brain mechanisms underlying speech and music may not only help dissociate the nature of these auditory processes in ASD but also provide a neurobiological basis for development of interventions. Using a passive‐listening functional magnetic resonance imaging paradigm with spoken words, sung words and piano tones, we found that 22 children with ASD, with varying levels of functioning, activated bilateral temporal brain networks during sung‐word perception, similarly to an age and gender‐matched control group. In contrast, spoken‐word perception was right‐lateralized in ASD and elicited reduced inferior frontal gyrus (IFG) activity which varied as a function of language ability. Diffusion tensor imaging analysis reflected reduced integrity of the left hemisphere fronto‐temporal tract in the ASD group and further showed that the hypoactivation in IFG was predicted by integrity of this tract. Subsequent psychophysiological interactions revealed that functional fronto‐temporal connectivity, disrupted during spoken‐word perception, was preserved during sung‐word listening in ASD, suggesting alternate mechanisms of speech and music processing in ASD. Our results thus demonstrate the ability of song to overcome the structural deficit for speech across the autism spectrum and provide a mechanistic basis for efficacy of song‐based interventions in ASD. Autism Res 2015, 8: 174–186.

Categorization of environmental sounds

Sounds in the natural environment are non-stationary, in that their spectral dynamics is time-dependent. We develop measures to analyze the spectral dynamics of environmental sound signals and find that they fall into two categories—simple sounds with slowly varying spectral dynamics and complex sounds with rapidly varying spectral dynamics. Based on our results and those from auditory processing we suggest rate of spectral dynamics as a possible scheme to categorize sound signals in the environment.

Are you a good mimic? Neuro-acoustic signatures for speech imitation ability

We investigated individual differences in speech imitation ability in late bilinguals using a neuro-acoustic approach. One hundred and thirty-eight German-English bilinguals matched on various behavioral measures were tested for “speech imitation ability” in a foreign language, Hindi, and categorized into “high” and “low ability” groups. Brain activations and speech recordings were obtained from 26 participants from the two extreme groups as they performed a functional neuroimaging experiment which required them to “imitate” sentences in three conditions: (A) German, (B) English, and (C) German with fake English accent. We used recently developed novel acoustic analysis, namely the “articulation space” as a metric to compare speech imitation abilities of the two groups. Across all three conditions, direct comparisons between the two groups, revealed brain activations (FWE corrected, p < 0.05) that were more widespread with significantly higher peak activity in the left supramarginal gyrus and postcentral areas for the low ability group. The high ability group, on the other hand showed significantly larger articulation space in all three conditions. In addition, articulation space also correlated positively with imitation ability (Pearsons r = 0.7, p < 0.01). Our results suggest that an expanded articulation space for high ability individuals allows access to a larger repertoire of sounds, thereby providing skilled imitators greater flexibility in pronunciation and language learning.

The development of articulatory signatures in children

The ability to perceive and produce sounds at multiple time scales is a skill necessary for the acquisition of language. Unlike speech perception, which develops early in life, the production of speech sounds starts at a few months and continues into late childhood with the development of speech-motor skills. Though there is detailed information available on early phonological development, there is very little information on when various articulatory features achieve adult-like maturity. We use modern spectral analysis to investigate the development of three language features associated with three different timescales in vocal utterances from typically developing children between 4 and 8 years. We make comparisons with adult speech and find age dependence in the appearance of these features. Results suggest that as children get older they exhibit increasingly more power in features associated with shorter time scales, thereby indicating the maturation of fine motor control in speech. Such data from typically developing children could provide milestones of speech production at different timescales. Since impairments in spoken language often provide the first warning signs of a language disorder we suggest that speech production could also be used to probe language disorders.

Emotional responses to Hindustani raga music: the role of musical structure

In Indian classical music, ragas constitute specific combinations of tonic intervals potentially capable of evoking distinct emotions. A raga composition is typically presented in two modes, namely, alaap and gat. Alaap is the note by note delineation of a raga bound by a slow tempo, but not bound by a rhythmic cycle. Gat on the other hand is rendered at a faster tempo and follows a rhythmic cycle. Our primary objective was to (1) discriminate the emotions experienced across alaap and gat of ragas, (2) investigate the association of tonic intervals, tempo and rhythmic regularity with emotional response. 122 participants rated their experienced emotion across alaap and gat of 12 ragas. Analysis of the emotional responses revealed that (1) ragas elicit distinct emotions across the two presentation modes, and (2) specific tonic intervals are robust predictors of emotional response. Specifically, our results showed that the ‘minor second’ is a direct predictor of negative valence. (3) Tonality determines the emotion experienced for a raga where as rhythmic regularity and tempo modulate levels of arousal. Our findings provide new insights into the emotional response to Indian ragas and the impact of tempo, rhythmic regularity and tonality on it.

Brains of verbal memory specialists show anatomical differences in language, memory and visual systems

We studied a group of verbal memory specialists to determine whether intensive oral text memory is associated with structural features of hippocampal and lateral-temporal regions implicated in language processing. Professional Vedic Sanskrit Pandits in India train from childhood for around 10years in an ancient, formalized tradition of oral Sanskrit text memorization and recitation, mastering the exact pronunciation and invariant content of multiple 40,000-100,000 word oral texts. We conducted structural analysis of gray matter density, cortical thickness, local gyrification, and white matter structure, relative to matched controls. We found massive gray matter density and cortical thickness increases in Pandit brains in language, memory and visual systems, including i) bilateral lateral temporal cortices and ii) the anterior cingulate cortex and the hippocampus, regions associated with long and short-term memory. Differences in hippocampal morphometry matched those previously documented for expert spatial navigators and individuals with good verbal working memory. The findings provide unique insight into the brain organization implementing formalized oral knowledge systems.

Rhythmic structure of Hindi and English: new insights from a computational analysis.

Much information about speech rhythm is believed to be embedded in low frequency temporal modulations of the speech envelope. Using novel methods of spectral analysis we construct a spectro-temporal modulation spectrum and extract low frequency temporal modulations of spoken utterances to study the rhythmic structure of English and Hindi. The results of our spectral analysis reveal a narrower temporal bandwidth for Hindi as compared to English. We also calculate variability in syllable durations and find that variability in English is greater than Hindi. We relate temporal bandwidth of the modulation spectrum to variability in syllable duration and suggest that narrow bandwidth in the modulation spectrum implies less variability, whereas broad bandwidth implies greater variability in syllable duration. Our results also demonstrate that syllabic information is contained in low frequency temporal modulations of the speech envelope. Our results suggest that the modulation spectrum can be explored as a promising tool to study the temporal structure of language.

The effect of sung speech on socio-communicative responsiveness in children with autism spectrum disorders.

There is emerging evidence to demonstrate the efficacy of music-based interventions for improving social functioning in children with Autism Spectrum Disorders (ASD). While this evidence lends some support in favor of using song over spoken directives in facilitating engagement and receptive intervention in ASD, there has been little research that has investigated the efficacy of such stimuli on socio-communicative responsiveness measures. Here, we present preliminary results from a pilot study which tested whether sung instruction, as compared to spoken directives, could elicit greater number of socio-communicative behaviors in young children with ASD. Using an adapted single-subject design, three children between the ages of 3 and 4 years, participated in a programme consisting of 18 sessions, of which 9 were delivered with spoken directives and 9 with sung. Sessions were counterbalanced and randomized for three play activities—block matching, picture matching and clay play. All sessions were video-recorded for post-hoc observational coding of three behavioral metrics which included performance, frequency of social gesture and eye contact. Analysis of the videos by two independent raters indicated increased socio-communicative responsiveness in terms of frequency of social gesture as well as eye contact during sung compared to spoken conditions, across all participants. Our findings suggest that sung directives may play a useful role in engaging children with ASD and also serve as an effective interventional medium to enhance socio-communicative responsiveness.