Influence of Lysergic Acid Diethylamide (LSD-25) on Subjective Time

Earlier reports have shown that people’s subjective sense of time can change markedly with external circumstances, and a smaller literature has examined how a person’s physical state alters time estimation. Clinical conditions such as fever and delirium are difficult to study systematically, but experimentally induced states—using agents such as nitrous oxide or mescaline—have provided more controlled evidence that perception of time can be altered. Lysergic acid diethylamide (LSD-25) has been described in observational reports as producing striking temporal distortions, including feelings of acceleration, retardation, or timelessness, but at least one systematic study had reported only increased variability without a directional shift in estimates. Aronson and colleagues designed an experimental study to test whether LSD-25 produces a consistent directional change in subjective time judgment under controlled conditions. The study aimed to compare time estimates made under LSD-25 with those made in the normal state, using a within-subjects design to reduce between-subject variability and to clarify discrepancies in the earlier literature.

Twenty-four male volunteers were screened by physical examination, psychiatric interview and group psychological testing and judged to be within normal limits. Subjects were allocated arbitrarily into two equal groups: one group was tested first under LSD-25 and later in the normal (control) state (Group D-C), and the other group received the conditions in the reverse order (Group C-D). The interval between the two test sessions ranged from three days to one week. Drug testing began two to three hours after ingestion of LSD-25. The extracted text does not clearly report the exact numerical microgram doses used; it states that two dose levels were administered and that three subjects in each group received the larger dose. No placebo was administered for the control condition. Four target time intervals were used for estimation: 15, 60, 120 and 240 minutes. Each subject produced each interval twice overall, once while under the drug and once in the normal state, giving eight judgements per subject. To minimise practice effects the order of the four intervals was varied individually so that no interval occupied a consistently privileged position across subjects. Subjects estimated intervals by the ‘‘method of production’’—they were told the length of time to estimate, given a signal to begin, and asked to tell the experimenter when the designated interval had elapsed. They were not permitted to use a watch or see the experimental stopwatch. Testing took place in a small room that was not soundproof and where sounds from an adjacent room could be heard. The authors analysed the data using non-parametric statistics (Mann-Whitney and Wilcoxon matched-pairs signed-ranks tests) after judging that assumptions of normality and homogeneity of variance were not met.

Initial analyses found no significant interaction between drug effect and the order of presentation (Mann-Whitney), so data from the two sequence groups were combined for the primary comparisons. Across both conditions subjects tended to overestimate the passage of clock time, but estimates were systematically different under LSD-25: subjects judged the required intervals to have elapsed more rapidly while on the drug than in the control condition. The authors interpret this pattern as reflecting a speeding of the subjects’ internal clocks under LSD-25, producing the paradoxical experience that external events seem to pass more slowly. Four cases were omitted from the paired analysis because the estimates under drug and control were identical. Using Wilcoxon matched-pairs tests on the remaining data, the authors report that time judgements at each interval were significantly shorter under LSD-25 than under the control condition. For the 15, 60 and 240 minute intervals the probability that the difference arose by chance was reported as less than 1 in 100 (p < 0.01), while for the 120 minute interval the probability was reported as less than 1 in 1,000 (p < 0.001).

Aronson and colleagues interpret their results as supporting a clear disturbance of temporal judgment during the LSD-25 reaction, consistent with clinical descriptions that time can feel altered under the drug. Rather than merely producing greater variability, the data indicated a consistent directional shift in the period studied (two to three hours after ingestion): subjects tended to complete produced intervals sooner under LSD-25, which the authors describe as an accelerated internal clock and a subjective slowing of external time. The investigators note several limitations and potential reasons their findings differ from Boardman and colleagues’ earlier null-directional result. One limitation is temporal sampling: their observations were confined to a specific 2–3 hour window after dosing, and the time-course of LSD-25’s effects might vary—initial slowing of some physiological regulator followed by speeding later could produce different results if sampling is more heterogeneous. Procedural differences may also matter: Boardman studied one-minute judgements using a series of stimuli that varied by 0.1 minute in ascending and descending order, a method that could introduce ‘‘perceptual rigidity’’—difficulty detecting small gradual changes—which might interact with LSD-induced concreteness of thinking and yield increased variability without a consistent bias. Another methodological contrast is the interval lengths used: very short intervals may rely on different cues and mechanisms than the longer intervals used here. On mechanisms, the authors discuss two broad hypotheses offered in the literature. One posits physiological ‘‘internal clock’’ regulators (for example heart rate or respiration rate) such that drug-induced changes in those regulators alter time perception. The alternative emphasises psychological appraisal—time seems to pass more slowly when experiences are unpleasant or uninteresting and more quickly when engaging—so the unusual qualitative character of psychedelic experience could influence judgements. The paper concludes that temporal orientation likely depends on a complex integration of multiple cues and that LSD-25’s broad disturbance of perceptual and conceptual functioning may impair either the reception of those cues or their integration, producing the observed changes in temporal judgment. In summary, within the constraints of the sampling window and procedures used, the study found a consistent shortening of produced intervals under LSD-25, i.e. a subjective slowing of external time, and discusses methodological and theoretical reasons for divergent findings in earlier work.