Biology subjects

Oganian, Y.

Publications and source records attributed to Oganian, Y..

10 recordsLinked to original sources

bioRxiv2026

Auditory timing precision is determined by spectro-temporal continuity across sounds, not individual sound acoustics

Predicting when an event will occur is key to perceiving and evaluating dynamic sensory inputs, such as speech. The utility of temporal predictions hinges on perceptual timing precision (PTP), the sensitivity to deviations between actual and predicted sound onset times. Past work suggests that PTP is primarily determined by acoustic properties of target sounds, regardless of the acoustics of preceding sound cues. In contrast, in four experiments, we discover that PTP is best when context and target sound spectra and temporal envelopes match, with only minor effects of individual sound acoustics. This ability to utilize contextual continuity improved with musical aptitude. Theoretical modeling showed that spectrally tuned oscillatory entrainment to sound onsets and offsets is necessary to account for our results. In sum, the precision of temporal predictions is defined not by the acoustics of individual sounds but by the continuity of spectral and temporal content within a sound stream.

neuroscience↗

bioRxiv2026

Word meaning, not surface statistics, is essential for predictive language processing

Next-word prediction is a key component of human language processing, which manifests itself in higher processing costs (longer reading times and enhanced neural responses) to unpredictable words. These costs are captured by large language model (LLM) surprisal, a metric inferred from statistical patterns of word co-occurrence. This makes word co-occurrence statistics a plausible candidate source for human next-word prediction. In contrast, psycholinguistic models posit that human next-word prediction relies on representations of word meaning. To contrast these views, we placed words that carry multiple meanings in contexts that rendered meaning ambiguous (e.g., 'My colleagues portrayed the head': body part or leader). With this, we kept word co-occurrence statistics available for prediction but introduced uncertainty into word meaning, effectively decorrelating these putative drivers of next-word prediction. Across three self-paced reading and magnetoencephalography (MEG) experiments, human processing costs for unpredictable unambiguous words were captured by LLM word surprisal, while ambiguity disrupted this relation. This shows that human next-word prediction is mechanistically linked to ambiguity resolution, diverging from LLM-like statistics-driven prediction specifically under ambiguity. We further found that a shared cortical network supports prediction and ambiguity resolution in parallel. Overall, our findings corroborate a distinctive feature of predictive language processing in humans, namely its reliance on word meaning beyond statistical patterns of word co-occurrence.

neuroscience↗

bioRxiv2026

Rapid neural analysis of linguistic stress and meter in continuous speech

Continuous speech evolves around vowels, the centerpieces of individual syllables. Vowels vary in linguistic and acoustic salience: Linguistically, stressed syllables are more salient than unstressed syllables: Stress patterns convey critical lexico-semantic and prosodic information, and their regularity defines the speech meter. Acoustically, English vowel intensity cues lexical stress but also marks salient syllables irrespective of stress status. Recent evidence demonstrates rapid neural analysis of vowel intensity and identity during perception of continuous speech. Here, we probe how these processes integrate lexical stress and metrical regularity. We recorded EEG while participants (n=26) listened to childrens stories with either an irregular, speech-like meter, or a regular poetic meter. Stress and meter modulated cortical encoding of vowels throughout processing: Preparatory activity preceded vowel onsets in an irregular meter only, and early sensory responses were enhanced for unstressed vowels, suggesting additional resource allocation during processing of uncertain and less discriminable speech sounds. In contrast, later processing (300-500ms) was stronger for stressed syllables and in irregular meters, suggesting a combined effect of uncertainty and informational content. Finally, responses were stronger for small intensity rises within metrically predicted stressed vowels than in all other conditions. In the time-frequency domain, the spectral profile of neural phase-locking corresponded to spectral signatures of individual evoked responses, syllable and stress rates in the stimuli. Overall, our findings reveal rapid neural integration of stress and metrical expectations in neural processing of continuous speech. These dynamics may underlie the perceptual benefits of metrically regular speech, such as poetry and song lyrics.

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bioRxiv2025

Discourse Focus and Memory Encoding: The Role of Trial-Level Alpha Power

The rapid, continuous flow of spoken language places strong demands on attention, and it is thought that listeners meet these demands by predicting when important information will occur and allocating attention accordingly. However, to date there is little direct evidence for the involvement of preparatory attention during language processing. In this study, we investigate preparatory attention during spoken language comprehension by measuring alpha neural activity with EEG, a known measure of temporal attentional preparation. Alpha activity leading up to target words that were either focused or defocused by a preceding discourse question did not vary as a function of focus, challenging the assumption that attention is pre-allocated to the timing of focused words. On the other hand, we found that trial-by-trial fluctuations in alpha activity predicted both the depth of processing and the subsequent memory for new information. Specifically, pre-target alpha modulated a centro-parietal Dm subsequent memory effect for focused words, linking preparatory attention to memory encoding during comprehension. Together, these findings bridge psycholinguistic studies on information structure and cognitive neuroscience research on temporal attention, offering novel insights into the role of alpha activity in attentional dynamics during spoken language processing.

neuroscience↗

bioRxiv2023

Anatomical and behavioral correlates of auditory perception in developmental dyslexia

Developmental dyslexia is typically associated with difficulties in basic auditory processing and in manipulating speech sounds. However, the neuroanatomical correlates of auditory difficulties in developmental dyslexia (DD) and their contribution to individual clinical phenotypes are still unknown. Recent intracranial electrocorticography findings associated processing of sound amplitude rises and speech sounds with posterior and middle superior temporal gyrus (STG), respectively. We hypothesize that regional STG anatomy will relate to specific auditory abilities in DD, and that auditory processing abilities will relate to behavioral difficulties with speech and reading. One hundred and ten children (78 DD, 32 typically developing, age 7-15 years) completed amplitude rise time and speech in noise discrimination tasks. They also underwent a battery of cognitive tests. Anatomical MRI scans were used to identify regions in which local cortical gyrification complexity correlated with auditory behavior. Behaviorally, amplitude rise time but not speech in noise performance was impaired in DD. Neurally, amplitude rise time and speech in noise performance correlated with gyrification in posterior and middle STG, respectively. Furthermore, amplitude rise time significantly contributed to reading impairments in DD, while speech in noise only explained variance in phonological awareness. Finally, amplitude rise time and speech in noise performance were not correlated, and each task was correlated with distinct neuropsychological measures, emphasizing their unique contributions to DD. Overall, we provide a direct link between the neurodevelopment of the left STG and individual variability in auditory processing abilities in neurotypical and dyslexic populations.

neuroscience↗

bioRxiv2022

Vowel and formant representation in human auditory speech cortex

Vowel sounds are a fundamental component of human speech across all languages. Vowels are cued acoustically by formants, the resonance frequencies determined by the shape of the vocal tract during speaking. An outstanding question in neurolinguistics is how the human brain processes vowel formants during speech perception. We used high-density intracranial recordings from the human speech cortex on the superior temporal gyrus (STG) while participants listened to natural continuous speech to address this question. We derived two-dimensional receptive fields based on the first and second formants to characterize tuning to vowel sounds. We found that neural activity at single STG sites was highly selective for particular zones in the formant space. Furthermore, this formant tuning shifted dynamically to adjust for speaker-specific spectral context. Despite this formant selectivity, local cortical responses were not sufficient to reliably discriminate between vowel categories. Instead, vowel category representations could be accurately decoded when using the entire population of formant encoding electrodes. Together, our results reveal that vowels are locally encoded in STG with complex acoustic tuning in two-dimensional formant space. As a population code this gives rise to phonological vowel perception.

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bioRxiv2021

Latent neural dynamics encode temporal context in speech

Direct neural recordings from human auditory cortex have demonstrated encoding for acoustic-phonetic features of consonants and vowels. Neural responses also encode distinct acoustic amplitude cues related to timing, such as those that occur at the onset of a sentence after a silent period or the onset of the vowel in each syllable. Here, we used a group reduced rank regression model to show that distributed cortical responses support a low-dimensional latent state representation of temporal context in speech. The timing cues each capture more unique variance than all other phonetic features and exhibit rotational or cyclical dynamics in latent space from activity that is widespread over the superior temporal gyrus. We propose that these spatially distributed timing signals could serve to provide temporal context for, and possibly bind across time, the concurrent processing of individual phonetic features, to compose higher-order phonological (e.g. word-level) representations.

neuroscience↗

bioRxiv2020

Topography of speech-related acoustic and phonological feature encoding throughout the human core and parabelt auditory cortex

Speech perception involves the extraction of acoustic and phonological features from the speech signal. How those features map out across the human auditory cortex is unknown. Complementary to noninvasive imaging, the high spatial and temporal resolution of intracranial recordings has greatly contributed to recent advances in our understanding. However, these approaches are typically limited by piecemeal sampling of the expansive human temporal lobe auditory cortex. Here, we present a functional characterization of local cortical encoding throughout all major regions of the primary and non-primary human auditory cortex. We overcame previous limitations by using rare direct recordings from the surface of the temporal plane after surgical microdissection of the deep Sylvian fissure between the frontal and temporal lobes. We recorded neural responses using simultaneous high-density direct recordings over the left temporal plane and the lateral superior temporal gyrus, while participants listened to natural speech sentences and pure tone stimuli. We found an anatomical separation of simple spectral feature tuning, including tuning for pure tones and absolute pitch, on the superior surface of the temporal plane, and complex tuning for phonological features, relative pitch and speech amplitude modulations on lateral STG. Broadband onset responses are unique to posterior STG and not found elsewhere in auditory cortices. This onset region is functionally distinct from the rest of STG, with latencies similar to primary auditory areas. These findings reveal a new, detailed functional organization of response selectivity to acoustic and phonological features in speech throughout the human auditory cortex.

neuroscience↗

bioRxiv2020

Low-frequency neural tracking of speech envelope reflects evoked responses to acoustic edges

The amplitude envelope of speech is crucial for accurate comprehension. Considered a key stage in speech processing, the phase of neural activity in the theta-delta bands (1 - 10 Hz) tracks the phase of the speech amplitude envelope during listening. However, the mechanisms underlying this envelope representation have been heavily debated. A dominant model posits that envelope tracking reflects entrainment of endogenous low-frequency oscillations to the speech envelope. Alternatively, envelope tracking reflects a series of evoked responses to acoustic landmarks within the envelope. It has proven challenging to distinguish these two mechanisms. To address this, we recorded magnetoencephalography while participants listened to natural speech, and compared the neural phase patterns to the predictions of two computational models: An oscillatory entrainment model and a model of evoked responses to peaks in the rate of envelope change. Critically, we also presented speech at slowed rates, where the spectrotemporal predictions of the two models diverge. Our analyses revealed transient theta phase-locking in regular speech, as predicted by both models. However, for slow speech we found transient theta and delta phase-locking, a pattern that was fully compatible with the evoked response model but could not be explained by the oscillatory entrainment model. Furthermore, encoding of acoustic edge magnitudes was invariant to contextual speech rate, demonstrating speech rate normalization of acoustic edge representations. Taken together, our results suggest that neural phase locking to the speech envelope is more likely to reflect discrete representation of transient information rather than oscillatory entrainment.

neuroscience↗

bioRxiv2018

A speech envelope landmark for syllable encoding in human superior temporal gyrus

Listeners use the slow amplitude modulations of speech, known as the envelope, to segment continuous speech into syllables. However, the underlying neural computations are heavily debated. We used high-density intracranial cortical recordings while participants listened to natural and synthesized control speech stimuli to determine how the envelope is represented in the human superior temporal gyrus (STG), a critical auditory brain area for speech processing. We found that the STG does not encode the instantaneous, moment-by-moment amplitude envelope of speech. Rather, a zone of the middle STG detects discrete acoustic onset edges, defined by local maxima in the rate-of-change of the envelope. Acoustic analysis demonstrated that acoustic onset edges reliably cue the information-rich transition between the consonant-onset and vowel-nucleus of syllables. Furthermore, the steepness of the acoustic edge cued whether a syllable was stressed. Synthesized amplitude-modulated tone stimuli showed that steeper edges elicited monotonically greater cortical responses, confirming the encoding of relative but not absolute amplitude. Overall, encoding of the timing and magnitude of acoustic onset edges in STG underlies our perception of the syllabic rhythm of speech.

neuroscience↗