A placebo-controlled investigation of synaesthesia-like experiences under LSD

This placebo-controlled within-subject study (n=10) investigated whether LSD (40–80μg/70kg) can induce synesthesia but found that it did not substantially alter the tendency to experience color concurrently in response to sounds and graphemes (letter or number that represents a sound in a word) and that the stimulus-color experiences did not meet accepted criteria for synaesthesia. Results suggest that LSD-induced synaesthesia-like experiences are qualitatively different from inborn/innate synaesthesia.

Abstract

“Introduction: The induction of synaesthesia in non-synaesthetes has the potential to illuminate the mechanisms that contribute to the development of this condition and the shaping of its phenomenology. Previous research suggests that lysergic acid diethylamide (LSD) reliably induces synaesthesia-like experiences in non-synaesthetes. However, these studies suffer from a number of methodological limitations including lack of a placebo control and the absence of rigorous measures used to test established criteria for genuine synaesthesia. Here we report a pilot study that aimed to circumvent these limitations.

Methods: We conducted a within-groups placebo-controlled investigation of the impact of LSD on colour experiences in response to standardized graphemes and sounds and the consistency and specificity of grapheme- and sound-colour associations.

Results: Participants reported more spontaneous synaesthesia-like experiences under LSD, relative to placebo, but did not differ across conditions in colour experiences in response to inducers, consistency of stimulus-colour associations, or in inducer specificity. Further analyses suggest that individual differences in a number of these effects were associated with the propensity to experience states of absorption in one’s daily life.

Discussion: Although preliminary, the present study suggests that LSD-induced synaesthesia-like experiences do not exhibit consistency or inducer-specificity and thus do not meet two widely established criteria for genuine synaesthesia.”

Authors: Devin B. Terhune, David P. Luke, Mendel Kaelen, Mark Bolstridge, Amanda Feilding, David Nutt, Robin Carhart-Harris & Jamie Ward

Summary

Abstract

This study aimed to circumvent methodological limitations of previous studies investigating LSD-induced synaesthesia by using a within-groups placebo-controlled investigation of colour experiences in response to standardized graphemes and sounds. The results suggest that LSD-induced synaesthesia-like experiences do not exhibit consistency or inducer-specificity and thus do not meet two widely established criteria for genuine synaesthesia.

1. Introduction

Synaesthesia is a condition in which a particular number or auditory tone automatically elicits a specific colour experience. The particular inducer-concurrent pairings that one experiences may be driven by environmental constraints.

LSD, psilocybin, and ayahausca have been shown to induce experiences that closely resemble synaesthesia in non-synaesthetes, but these studies suffer from numerous methodological limitations including the absence of placebo controls and the failure to use established behavioural measures of different features of synaesthesia. Researchers agree that synaesthesia is an automatic, consistent, specific, and accessible phenomenon. The review found that previous reports of LSD-induced synaesthesia-like experiences had not been formally tested to determine if they met the adjudication criteria of consistency and specificity.

Participants completed the OSIQ, a 30-item scale with a 5-point response format, and a 15-item subscale measuring object-spatial imagery, in each drug condition. Participants were presented with 25 unique symbols (digits 0-9 and 15 most frequent letters in the English language) and were asked to judge their colour experience in response to the symbols using the Perceptual Awareness Scale (PAS).

Participants were given a 10-ml solution of saline alone (placebo) or containing LSD (40 – 80 g) intravenously infused over a 3 min period. They completed a battery of psychological tasks and were assessed by a psychiatrist for suitability of discharge after the subjective effects of LSD had sufficiently subsided. We computed a measure of how reliably inducers elicited reports of colour experiences in the grapheme- and sound-colour tasks, and then analyzed the data using 2 -2 ANCOVAs and self-report measures as continuous covariates

3. Results

In a 2 condition, LSD condition, 2 task, repeated measures ANOVA, there were no main effects of Condition or Task, nor an interaction between Condition and Task.

Congenital synaesthesia is characterized by inducer-specificity, where lower values reflect greater correspondence between colour experiences across the different presentations of a stimulus in a particular condition (greater specificity). In the LSD condition, inducer-specificity was numerically lower, but there were no main effects of Condition or Task.

If LSD were inducing genuine synaesthesia, participants would have displayed numerically higher scores in the LSD condition in comparison with placebo, but there were neither main effects of Condition nor Task.

When three self-report measures were included as covariates, there was a Drug – Task – MODTAS interaction, which indicated that LSD increased grapheme-colour consistency scores more strongly than sound-colour consistency scores. Participants did not report synaesthetic experiences for all stimuli, and there were no main effects of Drug or Task, nor a Drug – Task interaction on beta coefficients. Higher absorption was associated with a tendency for colour awareness to be associated with higher consistency scores.

LSD induced synaesthesia-like experiences were more likely to be reported in participants who reported experiencing visual movements, experience of touch, and l ver forms, but not in participants who reported experiencing visual patterns, projector-like visual experiences, or control visual forms.

LSD-induced synaesthesia was investigated by scoring responses to sounds/symbols on a visual analogue scale with higher values reflecting stronger endorsement of the respective experience. This study sought to determine whether LSD-induced synaesthesia-like experiences met established criteria for the condition. The results suggest that LSD-induced synaesthesia-like experiences do not meet two established criteria for this condition.

In 15 studies of LSD-induced synaesthesia, participants reported spontaneous synaesthesia-like experiences more frequently in the LSD condition, but not in the placebo condition. In addition, participants did not exhibit greater inducer-concurrent consistency or inducer specificity in the LSD condition, relative to the placebo condition. Drug-induced synaesthesia-like experiences are plausible but different from congenital synaesthesia, as demonstrated by the fact that participants were able to detect which condition they were in. Another plausible explanation for the discrepant results is that the sample size did not offer sufficient statistical power to observe the induction of synaesthesia under LSD.

LSD may impair selective attention or attenuate distractor suppression, which may interfere with response patterns on this task. However, the same participants reported vivid visual experiences in response to music, which may suggest that richer stimuli are required to induce synaesthesia under LSD. In this study, participants reported spontaneous synaesthesia-like experiences. This finding is in line with previous reports of psychedelic drug-induced synaesthesia, where spontaneous occurrences of this phenomenon were related to the phenomenon rather than its induction via stimuli in a controlled experimental paradigm.

Investigating LSD-induced synaesthesia 17 phenomenon could be done by using experiential-sampling techniques, combined with simultaneous neuroimaging. Our inducer-concurrent consistency results, in particular, have some potentially important implications. They are at odds with the hypothesis that LSD is producing consistent synaesthesia-like experiences. The propensity for experiencing states of absorption appeared to moderate individual differences in a number of facets of stimulus-colour consistency, including the extent to which colour experiences predict stimulus-colour consistency. However, individuals exhibiting high absorption who experience LSD-induced colours will exhibit reduced stimulus-colour consistency.

LSD-induced synaesthesia-like experiences do not meet two established criteria for synaesthesia: inducer-specificity and stimulus-colour consistency. Thus, they should not be included in taxonomies of synaesthesia. A single critique of the criterion of inducer-concurrent consistency has been made, but it is likely that this criterion is too stringent for transient forms of synaesthesia, or early stages of this condition. The small sample size and ineffectiveness of the blind are limitations of this study. Further research may benefit from contrasting LSD with other psychoactive substances that will produce alterations in conscious states but not synaesthesia-like experiences.

A within-groups placebo-controlled study of LSD-induced synaesthesia did not show that LSD altered the tendency to experience colour concurrents in response to sounds and graphemes, and that stimulus-colour experiences under the influence of LSD did not meet accepted criteria for synaesthesia.