Purpose: Assess residual effects of MDMA (Ecstasy) and THC (marijuana) on perceived trajectory of travel. Methods: 42 licensed drivers (ages 21-42) participated: 12 MDMA/THC users, 15 THC users and 15 non-drug users. Drug use besides MDMA/THC was similar in both drug groups. There were no age, acuity (Sloane) or contrast sensitivity (Pelli-Robson) differences between groups. Perception of self-motion, or heading, from optical flow patterns was tested with stimuli comprising random dot ground planes presented at 3 densities (.035, .243 and .451 dots/ square degree) and 8 heading angles (1,2, 4 and 8 deg to the left or right). On each trial, subjects reported if direction of travel was to the left or the right relative to a vertical post whose position varied with respect to body midline (Warren et al., 1989). Right and left heading angles were combined into one score, as we expected no lateralized performance difference. Dependent measure was % correct. Results: Performance in all groups improved as heading angle increased; density had little effect. Plots of % correct vs. degrees of heading angle showed worse performance in both drug groups compared to controls at all but the 8 deg heading angle (P<0.05). The MDMA/THC group performed worst, especially at lower heading angles. Conclusions: Psychoactive agents appear to adversely affect visual perception, even in recently abstinent users, and appear to be additive in MDMA and THC. Precise mechanisms are unknown, but may involve serotonin and acetylcholine receptors in visual pathways. Residual effects may impair performance on driving-related tasks.
ASJC Scopus subject areas
- Sensory Systems