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1. A cortical network processes auditory error signals during human speech production to maintain fluency

   https://doi.org/10.1371/journal.pbio.3001493  

   Ozker, Muge; Doyle, Werner; Devinsky, Orrin; Flinker, Adeen (February 2022, PLOS Biology)

   Bizley, Jennifer K. (Ed.)

   Hearing one’s own voice is critical for fluent speech production as it allows for the detection and correction of vocalization errors in real time. This behavior known as the auditory feedback control of speech is impaired in various neurological disorders ranging from stuttering to aphasia; however, the underlying neural mechanisms are still poorly understood. Computational models of speech motor control suggest that, during speech production, the brain uses an efference copy of the motor command to generate an internal estimate of the speech output. When actual feedback differs from this internal estimate, an error signal is generated to correct the internal estimate and update necessary motor commands to produce intended speech. We were able to localize the auditory error signal using electrocorticographic recordings from neurosurgical participants during a delayed auditory feedback (DAF) paradigm. In this task, participants hear their voice with a time delay as they produced words and sentences (similar to an echo on a conference call), which is well known to disrupt fluency by causing slow and stutter-like speech in humans. We observed a significant response enhancement in auditory cortex that scaled with the duration of feedback delay, indicating an auditory speech error signal. Immediately following auditory cortex, dorsal precentral gyrus (dPreCG), a region that has not been implicated in auditory feedback processing before, exhibited a markedly similar response enhancement, suggesting a tight coupling between the 2 regions. Critically, response enhancement in dPreCG occurred only during articulation of long utterances due to a continuous mismatch between produced speech and reafferent feedback. These results suggest that dPreCG plays an essential role in processing auditory error signals during speech production to maintain fluency. 

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2. Rapid Learning and Long-term Memory in the Speech-to-song Illusion

   https://doi.org/10.1525/mp.2024.41.5.348  

   Kubit, Benjamin M; Deng, Christine; Tierney, Adam; Margulis, Elizabeth H (June 2024, Music Perception: An Interdisciplinary Journal)

   The speech-to-song illusion is a perceptual transformation in which a spoken phrase initially heard as speech begins to sound like song across repetitions. In two experiments, we tested whether phrase-specific learning and memory processes engaged by repetition contribute to the illusion. In Experiment 1, participants heard 16 phrases across two conditions. In both conditions, participants heard eight repetitions of each phrase and rated their experience after each repetition using a 10-point scale from “sounds like speech” to “sounds like song.” The conditions differed in whether the repetitions were heard consecutively or interleaved such that participants were exposed to other phrases between each repetition. The illusion was strongest when exposures to phrases happened consecutively, but phrases were still rated as more song-like after interleaved exposures. In Experiment 2, participants heard eight consecutive repetitions of each of eight phrases. Seven days later, participants were exposed to eight consecutive repetitions of the eight phrases heard previously as well as eight novel phrases. The illusion was preserved across a delay of one week: familiar phrases were rated as more song-like in session two than novel phrases. The results provide evidence for the role of rapid phrase-specific learning and long-term memory in the speech-to-song illusion. 

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3. Speech-induced suppression and vocal feedback sensitivity in human cortex

   https://doi.org/10.7554/eLife.94198.3  

   Ozker, Muge; Yu, Leyao; Dugan, Patricia; Doyle, Werner; Friedman, Daniel; Devinsky, Orrin; Flinker, Adeen (September 2024, eLife)

   Across the animal kingdom, neural responses in the auditory cortex are suppressed during vocalization, and humans are no exception. A common hypothesis is that suppression increases sensitivity to auditory feedback, enabling the detection of vocalization errors. This hypothesis has been previously confirmed in non-human primates, however a direct link between auditory suppression and sensitivity in human speech monitoring remains elusive. To address this issue, we obtained intracranial electroencephalography (iEEG) recordings from 35 neurosurgical participants during speech production. We first characterized the detailed topography of auditory suppression, which varied across superior temporal gyrus (STG). Next, we performed a delayed auditory feedback (DAF) task to determine whether the suppressed sites were also sensitive to auditory feedback alterations. Indeed, overlapping sites showed enhanced responses to feedback, indicating sensitivity. Importantly, there was a strong correlation between the degree of auditory suppression and feedback sensitivity, suggesting suppression might be a key mechanism that underlies speech monitoring. Further, we found that when participants produced speech with simultaneous auditory feedback, posterior STG was selectively activated if participants were engaged in a DAF paradigm, suggesting that increased attentional load can modulate auditory feedback sensitivity. 

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4. Categoricity, Variation, and Gradience in Sambla Balafon Segmental Encoding

   https://doi.org/10.3389/fcomm.2021.652635  

   McPherson, Laura (May 2021, Frontiers in Communication)

   null (Ed.)

   This paper analyzes the musical surrogate encoding of Seenku (Mande, Burkina Faso) syllable structure on the balafon, a resonator xylophone used by the Sambla ethnicity. The elements of syllable structure that are encoded include vowel length, sesquisyllabicity, diphthongs, and nasal codas. Certain elements, like vowel length and sesquisyllabicity, involve categorical encoding through conscious rules of surrogate speech, while others, like diphthongs and nasal codas, vary between being treated as simple or complex. Beyond these categorical encodings, subtler aspects of rhythmic structure find their way into the speech surrogate through durational differences; these include duration differences from phonemic distinctions like vowel length in addition to subphonemic differences due to phrasal position. I argue that these subconscious durational differences arise from a “phonetic filter”, which mediates between the musician’s inner voice and their non-verbal behavior. Specifically, syllables encoded on the balafon may be timed according to the perceptual center (p-center) of natural spoken rhythm, pointing to a degree of phonetic detail in a musician’s inner speech. 

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5. Development of vowel acoustics and subglottal resonances in American English-speaking children: A longitudinal Study

   https://doi.org/10.1121/10.0016294  

   Shetty, Vishwas; Lulich, Steven M.; Palo, Pertti; Alwan, Abeer (October 2022, The Journal of the Acoustical Society of America)

   Acoustic analysis of typically developing elementary school-aged (prepubertal) children’s speech has been primarily performed on cross-sectional data in the past. Few studies have examined longitudinal data in this age group. For this presentation, we analyze the developmental changes in the acoustic properties of children’s speech using data collected longitudinally over four years (from first grade to fourth grade). Four male and four female children participated in this study. Data were collected once every year for each child. Using these data, we measured the four-year development of subglottal acoustics (first two subglottal resonances) and vowel acoustics (first four formants and fundamental frequency). Subglottal acoustic measurements are relatively independent of context, and average values were obtained for each child in each year. Vowel acoustics measurements were made for seven vowels (i, ɪ, ɛ, æ, ʌ, ɑ, u), each occurring in two different words in the stressed syllable. We investigated the correlations between the children’s subglottal acoustics, vowel acoustics, and growth-related variables such as standing height, sitting height, and chronological age. Gender-, vowel-, and child-specific analyses were carried out in order to shed light on how typically developing speech acoustics depend on such variables. [Work supported, in part, by the NSF.] 

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