Motion and form perception in healthy individuals with adolescent cannabis use.

INTRODUCTION: Neuronal mechanisms of motion perception are susceptible to developmental anomalies. We tested whether heavy adolescent cannabis use is associated with enduring deficits in global motion perception, with relative sparing of global form perception, in abstinent adults. METHODS: In a cross-sectional study, 130 adults were enrolled: cannabis-naïve controls (n=50), non-heavy adolescent users (n=38), and heavy adolescent users (daily use before age 15; n=42). Participants reported no current psychoactive substance use and were in sustained remission from cannabis-related problems for ≥12 months. DSM-5 psychiatric disorders were excluded. Motion coherence (random-dot display) and form coherence (orientation-defined circles) thresholds were measured. Cannabis exposure was quantified with the Cannabis Exposure Inventory (CEI). RESULTS: The heavy-use group had higher motion coherence thresholds than controls and non-heavy users (p < 0.001; BF10 > 10, strong Bayesian evidence). Form coherence thresholds did not differ between groups. Non-heavy users did not differ from controls on either task. The CEI scores predicted motion coherence thresholds. CONCLUSIONS: Heavy cannabis exposure starting in early adolescence is associated with a selective deficit in global motion integration, consistent with the hypothesis of increased vulnerability of the dorsal visual stream. This hypothesis should be confirmed by longitudinal studies.