Alcohol Disrupted Eye Tracking in Ways That Cannabis Did Not
Alcohol impaired smooth eye tracking movements at multiple doses, while cannabis had no measurable effect on the same visual tracking tasks.
Quick Facts
What This Study Found
Researchers tested experienced substance users on a visual tracking task where participants followed a small moving dot with their eyes. The dot oscillated faster and faster until smooth tracking broke down.
Alcohol consistently degraded smooth eye tracking, reducing the frequency at which participants could maintain smooth pursuit. It also increased the time the brain needed to initiate saccadic (jumping) eye movements. These effects appeared dose-dependent.
Cannabis, by contrast, produced no measurable impairment on either smooth or saccadic tracking compared to placebo. The researchers attributed alcohol's effects to disruption of central processing in brainstem and cerebellar regions that coordinate eye movements.
Key Numbers
The tracking test ranged from 0.5 to 3.0 Hz over 40 seconds. The visual field span was 7.5 degrees. Alcohol reduced both smooth and saccadic cutoff frequencies; cannabis did not differ from placebo on either measure.
How They Did This
Experienced alcohol and cannabis users tracked a horizontally oscillating dot while eye movements were recorded. The dot's frequency increased from 0.5 to 3.0 Hz over 40 seconds. Researchers measured the frequency at which smooth tracking and saccadic tracking broke down under alcohol, cannabis, and placebo conditions.
Why This Research Matters
Eye tracking is used as a proxy for neurological impairment because it reflects how quickly the brain processes and responds to visual information. This study suggested cannabis and alcohol affect different neural pathways, with alcohol targeting brainstem and cerebellar structures involved in eye movement coordination while cannabis left those systems intact.
The Bigger Picture
This is one of several early studies attempting to identify which specific cognitive and motor functions cannabis impairs versus those it leaves intact. The finding that cannabis spared eye tracking while alcohol disrupted it helped researchers understand that these substances act on fundamentally different neural circuits.
What This Study Doesn't Tell Us
The study used experienced users who may have developed tolerance. The sample size was small. Only one type of visual tracking was tested, which does not capture all aspects of visual-motor coordination. The cannabis dose and route of administration were not detailed in the abstract.
Questions This Raises
- ?Do higher cannabis doses eventually impair eye tracking?
- ?Would cannabis-naive participants show different results?
- ?How do these eye tracking findings relate to real-world driving performance?
Trust & Context
- Key Stat:
- Cannabis produced no measurable impairment on smooth or saccadic eye tracking
- Evidence Grade:
- A controlled laboratory experiment with experienced users. Small sample and limited dosing detail reduce generalizability.
- Study Age:
- Conducted in 1976. Cannabis potency and consumption methods have changed substantially since this era.
- Original Title:
- Alcohol and marijuana effects on ocular tracking.
- Published In:
- American journal of optometry and physiological optics, 53(12), 764-73 (1976)
- Authors:
- Flom, M C(2), Brown, B, Adams, A J(2), Jones, R T
- Database ID:
- RTHC-00011
Evidence Hierarchy
Participants are randomly assigned to treatment or placebo groups to test cause and effect.
What do these levels mean? →Frequently Asked Questions
Did cannabis impair any aspect of eye tracking?
No. In this study, cannabis did not significantly affect either smooth pursuit or saccadic eye movements compared to placebo.
How did alcohol impair eye tracking?
Alcohol reduced the frequency at which smooth tracking could be maintained, increased the time needed to initiate saccadic eye movements, and slightly decreased saccadic velocity.
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Cite This Study
https://rethinkthc.com/research/RTHC-00011APA
Flom, M C; Brown, B; Adams, A J; Jones, R T. (1976). Alcohol and marijuana effects on ocular tracking.. American journal of optometry and physiological optics, 53(12), 764-73.
MLA
Flom, M C, et al. "Alcohol and marijuana effects on ocular tracking.." American journal of optometry and physiological optics, 1976.
RethinkTHC
RethinkTHC Research Database. "Alcohol and marijuana effects on ocular tracking." RTHC-00011. Retrieved from https://rethinkthc.com/research/flom-1976-alcohol-and-marijuana-effects
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.