Neural basis of learning to perceive speech through touch using an acoustic-to-vibrotactile speech sensory substitution

The goal of sensory substitution is to convey the information transduced by one sensory system through a novel sensory modality. One example is vibrotactile (VT) speech, for which acoustic speech is transformed into vibrotactile patterns. Despite an almost century-long history of studying vibrotactile speech, there has been no study of the neural bases of VT speech learning. We here trained hearing adult participants to recognize VT speech syllables. Using fMRI, we showed that both somatosensory (left post-central gyrus) and auditory (right temporal lobe) regions acquire selectivity for VT speech stimuli following training. The right planum temporale in particular was selective for both VT and auditory speech. EEG source-estimated activity revealed temporal dynamics consistent with direct, low-latency engagement of right temporal lobe following activation of the left post-central gyrus. Our results suggest that VT speech learning achieves integration with the auditory speech system by piggybacking onto corresponding auditory speech representations.

The vocal development of the pale spear-nosed bat is dependent on auditory feedback

Human vocal development and speech learning require acoustic feedback, and humans who are born deaf do not acquire a normal adult speech capacity. Most other mammals display a largely innate vocal repertoire. Like humans, bats are thought to be one of the few taxa capable of vocal learning as they can acquire new vocalizations by modifying vocalizations according to auditory experiences. We investigated the effect of acoustic deafening on the vocal development of the pale spear-nosed bat. Three juvenile pale spear-nosed bats were deafened, and their vocal development was studied in comparison with an age-matched, hearing control group. The results show that during development the deafened bats increased their vocal activity, and their vocalizations were substantially altered, being much shorter, higher in pitch, and more aperiodic than the vocalizations of the control animals. The pale spear-nosed bat relies on auditory feedback for vocal development and, in the absence of auditory input, species-atypical vocalizations are acquired. This work serves as a basis for further research using the pale spear-nosed bat as a mammalian model for vocal learning, and contributes to comparative studies on hearing impairment across species. This article is part of the theme issue ‘Vocal learning in animals and humans’.

Desenvolvimento fonético-fonológico bi/multilíngue e atenção – Questões teóricas abordadas no Speech Learning Model (SLM/SLM-r) e desafios futuros para a pesquisa em segunda língua (L2)

Neste artigo, propomos uma discussão teórica sobre as possíveis implicações atencionais no desenvolvimento fonético-fonológico bi/multilíngue. Para isso, partimos dos apontamentos feitos no Speech Learning Model, ao longo dos anos (FLEGE, 1995, 2003; FLEGE; BOHN, 2021), em relação ao componente cognitivo atencional. Discutiremos as seguintes questões latentes sobre atenção, não aprofundadas no SLM/SLM-r: (i) a possível relação direta entre proficiência e refinamento de categorias fonético-fonológicas; (ii) a conjugação entre percepção-produção, a qual perpassa, inevitavelmente, um contínuo de processamento entre armazenamento e recuperação de informações psico-acústicas; e (iii) o impacto metodológico de se considerar o construto ‘atenção’, associado ao SLM/SLM-r, nas coletas de dados de produção bilíngue. Tais lacunas psico-cognitivas dentro do modelo e, de forma geral, dentro da área de pesquisa, constituem desafios teóricos e metodológicos nos estudos de desenvolvimento bi/multilíngue, ainda mais numa perspectiva psicolinguística. Dessa forma, abrir o perímetro investigativo para questões mais amplas que envolvem a cognição bi/multilíngue pode contribuir, teórica e metodologicamente, para um maior entendimento do complexo processo de ensino-aprendizagem do componente fonético-fonológico de L2.

Articulatory settings and L2 English coronal consonants

Background/aims: We explore the potential contribution of Articulatory Settings (AS) theory to L2 speech production research, testing the hypothesis that L2 segmental speech learning should involve a gradual, overall shift in both place and constriction degree, simultaneously affecting all consonants of a series as opposed to a set of parallel but unrelated changes in learners’ production of individual sounds. Methods: We conducted an electropalatography study of four francophone learners’ production of French and English word-initial and -medial /t d s z n l/ via carrier-sentence reading tasks. Results: L1–L2 differences in tongue shape are more common than those in constriction location, first and foremost for sonorants, and, thus, our results are not completely consistent with AS theory’s claims. Conclusions: AS theory provides a potentially rich framework for exploring the L2 speech learning of consonantal phenomena including low-level L1–L2 differences in place of articulation. We propose that the observed lack of systematic between-language articulatory differences could be attributed to a number of factors to be explored in future research, such as the targeting of voicing and manner differences before the adjustment of small place differences as well as individual patterns of entrenchment of L1 articulatory routines.

Velopharyngeal dysfunction

This chapter explores velopharyngeal dysfunction (VPD), its impact, aetiology, assessment, and management. VPD may cause hypernasal, weak, and unintelligible speech, facial grimacing, nasal turbulence and nasal regurgitation, middle ear problems, and sinusitis. Such manifestations may be distressing for the patient, be associated with poor academic outcomes, be negatively perceived by others, lead to bullying and withdrawal, and result in relationship and employment difficulties. Like the effect of a visible difference on psychosocial confidence and self-esteem, the manifestations of VPD on emotional well-being and social interaction do not necessarily correlate with the amount of speech, language, or communication dysfunction. Normal anatomy, neuromotor function, and speech learning are prerequisites for effective velopharyngeal function. A problem with any of these components may result in a velopharyngeal mechanism that fails to efficiently and fully close throughout oral speech sound formation leading to VPD and an ensuing speech disorder. Perceptual speech evaluation is used to diagnose VPD. Lateral videofluoroscopy and nasoendoscopy are commonly deployed to assess velopharyngeal function and determine management strategies. Surgical interventions include pharyngoplasty, pharyngeal flaps, and velopharyngeal augmentation. Non-surgical interventions include speech prostheses and nasal obturators for speech improvement.

A Potential Role for Reinforcement Learning in Speech Production

Reinforcement learning, the ability to change motor behavior based on external reward, has been suggested to play a critical role in early stages of speech motor development and is widely used in clinical rehabilitation for speech motor disorders. However, no current evidence exists that demonstrates the capability of reinforcement to drive changes in human speech behavior. Speech provides a unique test of the universality of reinforcement learning across motor domains: Speech is a complex, high-dimensional motor task whose goals do not specify a task to be performed in the environment but ultimately must be self-generated by each speaker such that they are understood by those around them. Across four experiments, we examine whether reinforcement learning alone is sufficient to drive changes in speech behavior and parametrically test two features known to affect reinforcement learning in reaching: how informative the reinforcement signal is as well as the availability of sensory feedback about the outcomes of one's motor behavior. We show that learning does occur and is more likely when participants receive auditory feedback that gives an implicit target for production, although they do not explicitly imitate that target. Contrary to results from upper limb control, masking feedback about movement outcomes has no effect on speech learning. Together, our results suggest a potential role for reinforcement learning in speech but that it likely operates differently than in other motor domains.