arXiv subjects

Sidarta Ribeiro

Publications and source records attributed to Sidarta Ribeiro.

5 recordsLinked to original sources

arXiv2017

Comparative study of LSA vs Word2vec embeddings in small corpora: a case study in dreams database

Word embeddings have been extensively studied in large text datasets. However, only a few studies analyze semantic representations of small corpora, particularly relevant in single-person text production studies. In the present paper, we compare Skip-gram and LSA capabilities in this scenario, and we test both techniques to extract relevant semantic patterns in single-series dreams reports. LSA showed better performance than Skip-gram in small size training corpus in two semantic tests. As a study case, we show that LSA can capture relevant words associations in dream reports series, even in cases of small number of dreams or low-frequency words. We propose that LSA can be used to explore words associations in dreams reports, which could bring new insight into this classic research area of psychology

cs.CL↗

arXiv2016

The ontogeny of discourse structure mimics the development of literature

Discourse varies with age, education, psychiatric state and historical epoch, but the ontogenetic and cultural dynamics of discourse structure remain to be quantitatively characterized. To this end we investigated word graphs obtained from verbal reports of 200 subjects ages 2-58, and 676 literary texts spanning ~5,000 years. In healthy subjects, lexical diversity, graph size, and long-range recurrence departed from initial near-random levels through a monotonic asymptotic increase across ages, while short-range recurrence showed a corresponding decrease. These changes were explained by education and suggest a hierarchical development of discourse structure: short-range recurrence and lexical diversity stabilize after elementary school, but graph size and long-range recurrence only stabilize after high school. This gradual maturation was blurred in psychotic subjects, who maintained in adulthood a near-random structure. In literature, monotonic asymptotic changes over time were remarkable: While lexical diversity, long-range recurrence and graph size increased away from near-randomness, short-range recurrence declined, from above to below random levels. Bronze Age texts are structurally similar to childish or psychotic discourses, but subsequent texts converge abruptly to the healthy adult pattern around the onset of the Axial Age (800-200 BC), a period of pivotal cultural change. Thus, individually as well as historically, discourse maturation increases the range of word recurrence away from randomness.

q-bio.NC↗

arXiv2016

Quantifying word salad: The structural randomness of verbal reports predicts negative symptoms and Schizophrenia diagnosis 6 months later

Background: The precise quantification of negative symptoms is necessary to improve differential diagnosis and prognosis prediction in Schizophrenia. In chronic psychotic patients, the representation of verbal reports as word graphs provides automated sorting of schizophrenia, bipolar disorder and control groups based on the degree of speech connectedness. Here we aim to use machine learning to verify whether speech connectedness during first clinical contact can predict negative symptoms and Schizophrenia diagnosis six months later. Methods: PANSS scores and memory reports were collected from 21 patients undergoing first clinical contact for recent-onset psychosis and followed for 6 months to establish DSM-IV diagnosis, and 21 healthy controls. Each report was represented as a graph in which words corresponded to nodes, and node temporal succession corresponded to edges. Three connectedness attributes were extracted from each graph, z-scores to random graph distributions were measured, correlated with the PANSS negative subscale, combined into a single Fragmentation Index, and used for predictions. Findings: Random-like speech was prevalent among Schizophrenia patients (64% x 5% in Control group, p=0.0002). Connectedness explained 92% of the PANSS negative subscale variance (p=0.0001). The Fragmentation Index classified low versus high scores of PANSS negative subscale with 93% accuracy (AUC=1), predicted Schizophrenia diagnosis with 89% accuracy (AUC=0.89), and was validated in an independent cohort of chronic psychotic patients. Interpretation: The structural randomness of speech graph connectedness is increased in Schizophrenia. It provides a quantitative measurement of word salad as a Fragmentation Index that tightly correlates with negative symptoms and predicts Schizophrenia diagnosis during first clinical contact of recent-onset psychosis.

q-bio.NC↗

arXiv2016

Emotional Intensity analysis in Bipolar subjects

The massive availability of digital repositories of human thought opens radical novel way of studying the human mind. Natural language processing tools and computational models have evolved such that many mental conditions are predicted by analysing speech. Transcription of interviews and discourses are analyzed using syntactic, grammatical or sentiment analysis to infer the mental state. Here we set to investigate if classification of Bipolar and control subjects is possible. We develop the Emotion Intensity Index based on the Dictionary of Affect, and find that subjects categories are distinguishable. Using classical classification techniques we get more than 75\% of labeling performance. These results sumed to previous studies show that current automated speech analysis is capable of identifying altered mental states towards a quantitative psychiatry.

cs.AI↗

arXiv2011

Spike Avalanches Exhibit Universal Dynamics across the Sleep-Wake Cycle

Scale-invariant neuronal avalanches have been observed in cell cultures and slices as well as anesthetized and awake brains, suggesting that the brain operates near criticality, i.e. within a narrow margin between avalanche propagation and extinction. In theory, criticality provides many desirable features for the behaving brain, optimizing computational capabilities, information transmission, sensitivity to sensory stimuli and size of memory repertoires. However, a thorough characterization of neuronal avalanches in freely-behaving (FB) animals is still missing, thus raising doubts about their relevance for brain function. To address this issue, we employed chronically implanted multielectrode arrays (MEA) to record avalanches of spikes from the cerebral cortex (V1 and S1) and hippocampus (HP) of 14 rats, as they spontaneously traversed the wake-sleep cycle, explored novel objects or were subjected to anesthesia (AN). We then modeled spike avalanches to evaluate the impact of sparse MEA sampling on their statistics. We found that the size distribution of spike avalanches are well fit by lognormal distributions in FB animals, and by truncated power laws in the AN group. The FB data are also characterized by multiple key features compatible with criticality in the temporal domain, such as 1/f spectra and long-term correlations as measured by detrended fluctuation analysis. These signatures are very stable across waking, slow-wave sleep and rapid-eye-movement sleep, but collapse during anesthesia. Likewise, waiting time distributions obey a single scaling function during all natural behavioral states, but not during anesthesia. Results are equivalent for neuronal ensembles recorded from V1, S1 and HP. Altogether, the data provide a comprehensive link between behavior and brain criticality, revealing a unique scale-invariant regime of spike avalanches across all major behaviors.

q-bio.NC↗