The entropic tongue: Disorganization of natural language under LSD
Carhart-Harris, R. L., Carrillo, F., Copelli, M., Mota, N., Nutt, D. J., Pallavicini, C., Ribeiro, S., Sanz, C., Sigman, M., Tagliazucchi, E., Zamberlan, F.
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.
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.