The entropic tongue: Disorganization of natural language under LSD
This placebo-controlled study (n=20) suggests that speech produced under the influence of LSD (75 μg) exhibits more entropy than normal speech. This allowed machine learning programs to identify speech produced under the influence of LSD without analyzing semantic content.
Authors
- Enzo Tagliazucchi
- Robin Carhart-Harris
- David Nutt
Published
Abstract
Serotonergic psychedelics have been suggested to mirror certain aspects of psychosis, and, more generally, elicit a state of consciousness underpinned by increased entropy of ongoing neural activity. We investigated the hypothesis that language produced under the effects of lysergic acid diethylamide (LSD) should exhibit increased entropy and reduced semantic coherence. Computational analysis of interviews conducted at two different time points after 75 μg of intravenous LSD verified this prediction. Non-semantic analysis of speech organization revealed increased verbosity and a reduced lexicon, changes that are more similar to those observed during manic psychoses than in schizophrenia, which was confirmed by direct comparison with reference samples. Importantly, features related to language organization allowed machine learning classifiers to identify speech under LSD with accuracy comparable to that obtained by examining semantic content. These results constitute a quantitative and objective characterization of disorganized natural speech as a landmark feature of the psychedelic state.
Research Summary of 'The entropic tongue: Disorganization of natural language under LSD'
Introduction
Sanz and colleagues situate their study within two related lines of inquiry: first, that classic serotonergic psychedelics (acting at 5-HT2A receptors) profoundly alter consciousness and have historically been considered “psychotomimetic”; and second, the entropic brain hypothesis, which proposes that psychedelics raise the entropy or unpredictability of ongoing neural activity. Earlier work reported that psychedelics render speech less predictable and enhance free association, but contemporary, quantitative analyses of natural, spontaneous speech under psychedelics have been scarce. This study set out to test the central hypothesis that speech produced during the acute effects of lysergic acid diethylamide (LSD) would show increased markers of disorganization relative to placebo. To do so, the investigators applied automated natural language processing and graph-theoretical methods to transcribed interview material, using Shannon information entropy, Word2Vec-based semantic coherence measures, a novel embedding-rank (compressibility) metric, speech-graph topology, a previously defined disorganization index, and machine-learning classifiers to distinguish LSD from placebo speech. The aim was both to quantify speech disorganisation in the psychedelic state and to compare its profile with speech patterns seen in psychotic disorders.
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Study Details
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- APA Citation
Sanz, C., Pallavicini, C., Carrillo, F., Zamberlan, F., Sigman, M., Mota, N., Copelli, M., Ribeiro, S., Nutt, D., Carhart-Harris, R., & Tagliazucchi, E. (2021). The entropic tongue: Disorganization of natural language under LSD. Consciousness and Cognition, 87, 103070. https://doi.org/10.1016/j.concog.2020.103070
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