Biology subjects

Ravignani, A.

Publications and source records attributed to Ravignani, A..

10 recordsLinked to original sources

bioRxiv2026

Emergent Entrainment and Predictive Dynamics in Bio-Inspired Spiking Neural Networks

Rhythm is a key building block of human music, speech and numerous other human activities. Understanding the computational substrates of rhythm perception requires models that bridge algorithmic function with biological implementation. We propose a physiologically grounded spiking neural network (SNN) framework to investigate the emergent representation and interpretation of auditory rhythms. Utilizing a recurrent SNN architecture trained on an auditory entrainment task, we characterize the networks latent dynamics through the analysis of firing rates and membrane potential fluctuations. Our results demonstrate that simulated neural populations exhibit phase-locking to the stimulus beat, with endogenous oscillations driven by rhythmic input. We further show that anticipatory dynamics--characterized by pre-stimulus depolarization--emerge naturally from the networks synaptic plasticity and temporal integration properties, rather than from explicitly defined oscillators. By treating network layers as functional analogs of cortical populations, this framework allows for the application of spectral and information-theoretic analyses typical of empirical electrophysiology. More in general, this approach establishes SNNs as robust exploratory tools for uncovering how predictive coding and rhythmic entrainment arise from the inherent constraints of biological neural computation.

neuroscience↗

bioRxiv2025

Accelerando and crescendo in African penguin display songs

Many species produce rhythmic sound sequences. Some purportedly speed up their vocalizations throughout a display, reminiscent of--but not necessarily equivalent to-- "accelerando" in human music. This phenomenon has been frequently reported but rarely quantified, which limits our ability to understand its mechanism, function, and evolution. Here, we use a suite of rhythm analyses to quantify temporal and acoustic features in the display songs of male African penguins (Spheniscus demersus). We show that songs get faster (i.e., accelerando) and louder (i.e., crescendo) as they progress. The accelerando occurs because the inter-syllable silences, not the syllables themselves, predictably shorten over time. This rhythmicity is maintained even when individuals take audible breaths. Individuals also show plasticity: when they start with a slow tempo, they speed up more strongly than when they start with a fast tempo. We hypothesize that this well-timed accelerando may stem from arousal-based mechanisms, biomechanical constraints, or more complex rhythmic control; future work should test the mechanisms behind this intra-individual rhythmic variation, since non-passerine birds are thought to have limited vocal plasticity. By integrating a rich empirical dataset with cutting-edge rhythm analyses, we establish the necessary foundation to determine how such features evolved and their role(s) across communication systems.

animal behavior and cognition↗

bioRxiv2024

Training Harbor Seals to Participate in Vocal Learning Experiments in a Zoo

Harbor seals (Phoca vitulina) are a common zoo species that show a scientifically valuable propensity for vocal learning. Under human care, the seals can be trained to associate vocalizations with cues. This ability is termed vocal usage learning and is characterized by learning to use a vocalization in a specific context. Among mammals, seals are prime candidates to investigate vocal learning. Yet, only a handful of reports exist on harbor seal vocal learning abilities, and even fewer document how these were trained or tested. Here, we investigate how, and if, two experimentally naive harbor seals under human care can be trained to participate in scientific experiments. We describe the training and testing of two seals in two basic vocal learning experiments. We trained the animals to vocalize upon the presentation of discriminative stimuli (SD) through operant conditioning methods and tested their abilities to i) vocalize and refrain from vocalizing on two distinct SDs, and ii) produce two different vocalizations upon the presentation of two different SDs. Both seals learned the tasks: the first task was achieved within 118 trials (22 errors to criterion) and 220 trials (40 errors to criterion), the second task within 480 trials (158 errors to criterion) and 380 trials (94 errors to criterion), respectively. Our results confirm that harbor seals are capable of vocal usage learning and further suggest that associating individually distinct vocalizations with different SDs may be more cognitively demanding than vocalizing and being silent on SD.

animal behavior and cognition↗

bioRxiv2023

Recursive self-embedded vocal motifs in wild orangutans

Recursive procedures that allow placing a vocal signal inside another of similar kind provide a neuro-computational blueprint for syntax and phonology in spoken language and human song. There are, however, no known vocal sequences among nonhuman primates arranged in self-embedded patterns that evince vocal recursion or potential insipient or evolutionary transitional forms thereof, suggesting a neuro-cognitive transformation exclusive to humans. Here, we uncover that wild flanged male orangutan long calls feature rhythmically isochronous call sequences nested within isochronous call sequences, consistent with two hierarchical strata. Remarkably, three temporally and acoustically distinct call rhythms in the lower stratum were not related to the overarching rhythm at the higher stratum by any low multiples, which suggests that these recursive structures were neither the result of parallel non-hierarchical procedures or anatomical artifacts of bodily constrains or resonances. Findings represent a case of temporally recursive hominid vocal combinatorics in the absence syntax, semantics, phonology or music. Second-order combinatorics, sequences within sequences, involving hierarchically organized and cyclically structured vocal sounds in ancient hominids may have preluded the evolution of recursion in modern language-able humans.

animal behavior and cognition↗

bioRxiv2021

Vocal tract allometry in a mammalian vocal learner

Acoustic allometry occurs when features of animal vocalisations can be predicted from body size measurements. Despite this being considered the norm, allometry sometimes breaks, resulting in species sounding smaller or larger than expected for their size. A recent hypothesis suggests that allometry-breaking mammals cluster into two groups: those with anatomical adaptations to their vocal tracts and those capable of learning new sounds (vocal learners). Here we test which mechanism is used to escape from acoustic allometry by probing vocal tract allometry in a proven mammalian vocal learner, the harbour seal (Phoca vitulina). We test whether vocal tract structures and body size scale allometrically in 68 young individuals. We find that both body length and body mass accurately predict vocal tract length and one tracheal dimension. Independently, body length predicts vocal fold length while body mass predicts a second tracheal dimension. All vocal tract measures are larger in weaners than in pups and some structures are sexually dimorphic within age classes. We conclude that harbour seals do comply with anatomical allometric constraints. However, allometry between body size and vocal fold length seems to emerge after puppyhood, suggesting that ontogeny may modulate the anatomy-learning distinction previously hypothesised as clear-cut. We suggest that seals, like other species producing signals that deviate from those expected from their vocal tract dimensions, may break allometry without morphological adaptations. In seals, and potentially other vocal learning mammals, advanced neural control over vocal organs may be the main mechanism for breaking acoustic allometry.

animal behavior and cognition↗

bioRxiv2021

Vocal plasticity in harbour seal pups

Vocal plasticity can occur in response to environmental and biological factors, including conspecifics vocalisations and noise. Pinnipeds are one of the few mammalian groups capable of vocal learning, and are therefore relevant to understanding the evolution of vocal plasticity in humans and other animals. Here, we investigate the vocal plasticity of harbour seals (Phoca vitulina), a species with vocal learning abilities attested in adulthood but not puppyhood. To zoom into early mammalian vocal development, we tested 1-3 weeks old seal pups. We tailored noise playbacks to this species and age to induce seal pups to shift their fundamental frequency (F0), rather than adapt call amplitude or temporal characteristics. We exposed individual pups to bandpass-filtered noise, which purposely spanned - and masked - their typical range of F0s, and simultaneously recorded pups spontaneous calls. Seals were able to modify their vocalisations quite unlike most mammals: They lowered their F0 in response to increased noise. This modulation was punctual and adapted to the particular noise condition. In addition, higher noise induced less dispersion around the mean F0, suggesting that pups may have been actively focusing their phonatory efforts to target lower frequencies. Noise masking did not seem to affect call amplitude. However, one seal showed two characteristics of the Lombard effect known for human speech in noise: significant increase in call amplitude and flattening of spectral tilt. Our relatively low noise levels may have favoured F0 shifts while inhibiting amplitude adjustments. This lowering of F0 is quite unusual, as other animals commonly display no F0 shift independently of noise amplitude. Our data represents a relatively rare case in mammalian neonates, and may have implications for the evolution of vocal plasticity across species, including humans.

animal behavior and cognition↗

bioRxiv2020

Neuroanatomy of the grey seal brain: bringing pinnipeds into the neurobiological study of vocal learning

Comparative studies of vocal learning and vocal non-learning animals can increase our understanding of the neurobiology and evolution of vocal learning and human speech. Mammalian vocal learning is understudied: most research has either focused on vocal learning in songbirds or its absence in non-human primates. Here we focus on a highly promising model species for the neurobiology of vocal learning: grey seals. We provide a neuroanatomical atlas (based on dissected brain slices and magnetic resonance images), a labelled MRI template, a 3D model with volumetric measurements of brain regions, and histological cortical stainings. Four main features of the grey seal brain stand out. (1) It is relatively big and highly convoluted. (2) It hosts a relatively large temporal lobe and cerebellum, structures which could support developed timing abilities and acoustic processing. (3) The cortex is similar to humans in thickness and shows the expected six-layered mammalian structure. (4) Expression of FoxP2 - a gene involved in vocal learning and spoken language - is present in deeper layers of the cortex. Our results could facilitate future studies targeting the neural and genetic underpinnings of mammalian vocal learning, thus bridging the research gap from songbirds to humans and non-human primates.

animal behavior and cognition↗

bioRxiv2019

Evolutionary Dynamics Do Not Motivate a Single-Mutant Theory of Human Language

AbstractOne of the most controversial hypotheses in cognitive science is the Chomskyan evolutionary conjecture that language arose instantaneously in our species as the result of a single staggeringly fortuitous mutation. Here we analyze the evolutionary dynamics implied by this hypothesis, which has never been formalized. The theory supposes the emergence and fixation of a single mutant (capable of the syntactic operation Merge) during a narrow historical window as a result of frequency-independent selection under a huge fitness advantage in a population of an effective size that is standardly assumed to have been no larger than ~15 000 early humans. We examine this proposal by combining diffusion analysis and extreme value theory to derive a probabilistic formulation of its dynamics. Perhaps counter-intuitively, a macro-mutation is much more unlikely a priori than multiple mutations with smaller fitness effects, yet both hypotheses predict fixation with high conditional probability. The consequences of this asymmetry have not been accounted for previously. Our results diffuse any suggestion that evolutionary reasoning provides an independent rationale for the controversial single-mutant theory of language.\n\nSignificance statementIn recent years, Chomsky and colleagues have sought support for their minimalist theory of the language faculty from evolutionary considerations. They have argued for a spontaneous emergence of a mutation conferring an advantage for thought independent of communication. Here for the first time a formalization of this view is offered, and contrasted with a more gradual evolutionary scenario. The outcome of our analysis argues against the Chomskyan view.

evolutionary biology↗

bioRxiv2017

Evolving building blocks of rhythm: How human cognition creates music via cultural transmission

Musical rhythm, in all its cross-cultural diversity, exhibits several commonalities across world cultures. Traditionally, music research has been split in two fields. Some scientists focused on musicality, namely the human biocognitive predispositions for music, with an emphasis on cross-cultural similarities. Other scholars investigated music, seen as cultural product, focusing on the large variation in world musical cultures. Recent experiments found deep connections between music and musicality, reconciling these opposing views. Here we address the question of how individual cognitive biases affect the process of cultural evolution of music. Data from two experiments is analyzed using two different, complementary techniques. In the experiments, participants hear drumming patterns and imitate them. These patterns are then given to the same or another participant to imitate. The structure of these - initially random - patterns is tracked down to later experimental generations. Frequentist statistics show how participants biases are amplified by cultural transmission, making drumming patterns more structured. Structure is achieved faster than in transmission within, rather than between, participants. A Bayesian model approximates the motif structures participants learned and created. Overall, our data and model show that individual biases for musicality play a central role in shaping cultural transmission of musical rhythm.

animal behavior and cognition↗

bioRxiv2017

Positional encoding in cotton-top tamarins (Saguinus oedipus)

Strategies used in artificial grammar learning can shed light into the abilities of different species to extract regularities from the environment. In the A(X)nB rule, A and B items are linked but assigned to different positional categories and separated by distractor items. Open questions are how widespread is the ability to extract positional regularities from A(X)nB patterns, which strategies are used to encode positional regularities and whether individuals exhibit preferences for absolute or relative position encoding. We used visual arrays to investigate whether cotton-top tamarins (Saguinus oedipus) can learn this rule and which strategies they use. After training on a subset of exemplars, half of the tested monkeys successfully generalized to novel combinations. These tamarins discriminated between categories of tokens with different properties (A, B, X) and detected a positional relationship between non-adjacent items even in the presence of novel distractors. Generalization, though, was incomplete, since we observed a failure with items that during training had always been presented in reinforced arrays. The pattern of errors revealed that successful subjects used visual similarity with training stimuli to solve the task, and that tamarins extracted the relative position of As and Bs rather than their absolute position, similarly to what observed in other species. Relative position encoding appears to be the default strategy in different tasks and taxa.

animal behavior and cognition↗