Longitudinal trajectories of electrophysiological mismatch responses in infant speech discrimination differ across speech features.

Infants rapidly advance in their speech perception, electrophysiologically reflected in the transition from an immature, positive-going to an adult-like, negative-going mismatch response (MMR) to auditory deviancy. Although the MMR is a common tool to study speech perception development, it is not yet completely understood how different speech contrasts affect the MMR's characteristics across development. Thus, a systematic longitudinal investigation of the MMR's maturation depending on speech contrast is necessary. We here longitudinally explored the maturation of the infant MMR to four critical speech contrasts: consonant, vowel, vowel-length, and pitch. MMRs were obtained when infants (n = 58) were 2, 6 and 10 months old. To evaluate the maturational trajectory of MMRs, we applied second-order latent growth curve models. Results showed positive-going MMR amplitudes to all speech contrasts across all assessment points that decreased over time towards an adult-like negativity. Notably, the developmental trajectories of speech contrasts differed, implying that infant speech perception matures with different rates and trajectories throughout the first year, depending on the studied auditory feature. Our results suggest that stimulus-dependent maturational trajectories need to be considered when drawing conclusions about infant speech perception development reflected by the infant MMR.

Musical meaning modulates word acquisition.

Musical excerpts have been shown to have the capacity to prime the processing of target words and vice versa, strongly suggesting that music can convey concepts. However, to date no study has investigated an influence of musical semantics on novel word acquisition, thus corroborating evidence for a similarity of underlying semantic processing of music and words behaviourally. The current study investigates whether semantic content of music can assist the acquisition of novel words. Forty novel words and their German translation were visually presented to 26 participants accompanied by either semantically congruent or incongruent music. Semantic congruence between music and words was expected to increase performance in the subsequent forced-choice recognition test. Participants performed significantly better on the retention of novel words presented with semantically congruent music compared to those presented with semantically incongruent music. This provides first evidence that semantic "enrichment" by music during novel word learning can augment novel word acquisition. This finding may lead to novel approaches in foreign language acquisition and language rehabilitation, and further strongly supports the concept that music has a strong capacity to iconically convey meaning.

Gait improvement via rhythmic stimulation in Parkinson's disease is linked to rhythmic skills.

Training based on rhythmic auditory stimulation (RAS) can improve gait in patients with idiopathic Parkinson's disease (IPD). Patients typically walk faster and exhibit greater stride length after RAS. However, this effect is highly variable among patients, with some exhibiting little or no response to the intervention. These individual differences may depend on patients' ability to synchronize their movements to a beat. To test this possibility, 14 IPD patients were submitted to RAS for four weeks, in which they walked to music with an embedded metronome. Before and after the training, patients' synchronization was assessed with auditory paced hand tapping and walking to auditory cues. Patients increased gait speed and stride length in non-cued gait after training. However, individual differences were apparent as some patients showed a positive response to RAS and others, either no response, or a negative response. A positive response to RAS was predicted by the synchronization performance in hand tapping and gait tasks. More severe gait impairment, low synchronization variability, and a prompt response to a stimulation change foster a positive response to RAS training. Thus, sensorimotor timing skills underpinning the synchronization of steps to an auditory cue may allow predicting the success of RAS in IPD.

Universal and language-specific sublexical cues in speech perception: a novel electroencephalography-lesion approach.

SEE CAPPA DOI101093/BRAIN/AWW090 FOR A SCIENTIFIC COMMENTARY ON THIS ARTICLE : The phonological structure of speech supports the highly automatic mapping of sound to meaning. While it is uncontroversial that phonotactic knowledge acts upon lexical access, it is unclear at what stage these combinatorial rules, governing phonological well-formedness in a given language, shape speech comprehension. Moreover few studies have investigated the neuronal network affording this important step in speech comprehension. Therefore we asked 70 participants-half of whom suffered from a chronic left hemispheric lesion-to listen to 252 different monosyllabic pseudowords. The material models universal preferences of phonotactic well-formedness by including naturally spoken pseudowords and digitally reversed exemplars. The latter partially violate phonological structure of all human speech and are rich in universally dispreferred phoneme sequences while preserving basic auditory parameters. Language-specific constraints were modelled in that half of the naturally spoken pseudowords complied with the phonotactics of the native language of the monolingual participants (German) while the other half did not. To ensure universal well-formedness and naturalness, the latter stimuli comply with Slovak phonotactics and all stimuli were produced by an early bilingual speaker. To maximally attenuate lexico-semantic influences, transparent pseudowords were avoided and participants had to detect immediate repetitions, a task orthogonal to the contrasts of interest. The results show that phonological 'well-formedness' modulates implicit processing of speech at different levels: universally dispreferred phonological structure elicits early, medium and late latency differences in the evoked potential. On the contrary, the language-specific phonotactic contrast selectively modulates a medium latency component of the event-related potentials around 400 ms. Using a novel event-related potential-lesion approach allowed us to furthermore supply first evidence that implicit processing of these different phonotactic levels relies on partially separable brain areas in the left hemisphere: contrasting forward to reversed speech the approach delineated an area comprising supramarginal and angular gyri. Conversely, the contrast between legal versus illegal phonotactics consistently projected to anterior and middle portions of the middle temporal and superior temporal gyri. Our data support the notion that phonological structure acts on different stages of phonologically and lexically driven steps of speech comprehension. In the context of previous work we propose context-dependent sensitivity to different levels of phonotactic well-formedness.

Facilitation of inferior frontal cortex by transcranial direct current stimulation induces perceptual learning of severely degraded speech.

Perceptual learning requires the generalization of categorical perceptual sensitivity from trained to untrained items. For degraded speech, perceptual learning modulates activation in a left-lateralized network, including inferior frontal gyrus (IFG) and inferior parietal cortex (IPC). Here we demonstrate that facilitatory anodal transcranial direct current stimulation (tDCS(anodal)) can induce perceptual learning in healthy humans. In a sham-controlled, parallel design study, 36 volunteers were allocated to the three following intervention groups: tDCS(anodal) over left IFG, IPC, or sham. Participants decided on the match between an acoustically degraded and an undegraded written word by forced same-different choice. Acoustic degradation varied in four noise-vocoding levels (2, 3, 4, and 6 bands). Participants were trained to discriminate between minimal (/Tisch/-FISCH) and identical word pairs (/Tisch/-TISCH) over a period of 3 d, and tDCS(anodal) was applied during the first 20 min of training. Perceptual sensitivity (d') for trained word pairs, and an equal number of untrained word pairs, was tested before and after training. Increases in d' indicate perceptual learning for untrained word pairs, and a combination of item-specific and perceptual learning for trained word pairs. Most notably for the lowest intelligibility level, perceptual learning occurred only when tDCS(anodal) was applied over left IFG. For trained pairs, improved d' was seen on all intelligibility levels regardless of tDCS intervention. Over left IPC, tDCS(anodal) did not modulate learning but instead introduced a response bias during training. Volunteers were more likely to respond "same," potentially indicating enhanced perceptual fusion of degraded auditory with undegraded written input. Our results supply first evidence that neural facilitation of higher-order language areas can induce perceptual learning of severely degraded speech.

Sensitivity of newborn auditory cortex to the temporal structure of sounds.

Understanding the rapidly developing building blocks of speech perception in infancy requires a close look at the auditory prerequisites for speech sound processing. Pioneering studies have demonstrated that hemispheric specializations for language processing are already present in early infancy. However, whether these computational asymmetries can be considered a function of linguistic attributes or a consequence of basic temporal signal properties is under debate. Several studies in adults link hemispheric specialization for certain aspects of speech perception to an asymmetry in cortical tuning and reveal that the auditory cortices are differentially sensitive to spectrotemporal features of speech. Applying concurrent electrophysiological (EEG) and hemodynamic (near-infrared spectroscopy) recording to newborn infants listening to temporally structured nonspeech signals, we provide evidence that newborns process nonlinguistic acoustic stimuli that share critical temporal features with language in a differential manner. The newborn brain preferentially processes temporal modulations especially relevant for phoneme perception. In line with multi-time-resolution conceptions, modulations on the time scale of phonemes elicit strong bilateral cortical responses. Our data furthermore suggest that responses to slow acoustic modulations are lateralized to the right hemisphere. That is, the newborn auditory cortex is sensitive to the temporal structure of the auditory input and shows an emerging tendency for functional asymmetry. Hence, our findings support the hypothesis that development of speech perception is linked to basic capacities in auditory processing. From birth, the brain is tuned to critical temporal properties of linguistic signals to facilitate one of the major needs of humans: to communicate.