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Research & Development Adverse effects, Medical research

Like, Totally, Man

Of all the stereotypes about marijuana, few are as pervasive as the “stoner voice.” Though research has found that depressants or hallucinogenic drugs can cause acute changes in communication and speech rate, the long-lasting effects of cannabis are not well described. But researchers are setting the record straight.

This study compared speech samples of individuals with a history of recreational cannabis use to non-drug-using healthy controls. A total of 31 adults with a history of cannabis use (but not use of illicit stimulant drugs) and 40 non-drug-using controls completed simple and complex speech tasks including a monologue, a sustained vowel, saying the days of the week, and reading a phonetically balanced passage. Audio samples were then objectively assessed using acoustic analysis for measures of timing, vocal control, and quality.

The result? Subtle differences in speech timing, vocal effort, and voice quality may exist between cannabis and control groups; however (and this is the kicker) data remain equivocal. Interestingly, after controlling for lifetime alcohol and tobacco use and applying a false discovery rate, only spectral tilt (otherwise known as vocal effort and intensity) differed between groups and appeared to change in line with duration of abstinence from cannabis use. The team suggest the differences between groups may reflect longer term changes to the underlying neural control of speech. Further analysis showed that there may be a signal differentiating individuals with a history of recreational cannabis use from healthy controls, in line with similar findings from gait and hand function studies.

Adam Vogel, Professor and Director, Centre for Neuroscience of Speech, The University of Melbourne, Australia, and co-lead author of the study, explains.

Q&A

Where do you think the myth of "slow and labored" speech came from?

Sean Penn’s character Jeff Spicoli in ‘Fast Times at Ridgemont High’ is partly responsible, but the stereotype is likely based on people ‘on the drug’. 

Were these subtle differences perceptible without analysis equipment?

We didn’t test the ability of listeners to detect differences, but it’s unlikely that these subtle group differences are perceivable to the human ear. Working on the assumption that the digital speech measurements are able to objectively detect tiny changes in performance, the tools we used here are more reliable (humans are notoriously unreliable when rating and observing behaviours) and sensitive than we are.

Is there a reason only spectral tilt differed between groups?

There were a number of differences between groups including variability of pause length, loudness control as well as the measure of spectral tilt. Spectral tilt is a summative feature that includes measures of stress and voice quality and is captured by examining energy distribution across low and high frequencies. It has also shown sensitivity to fatigue, perhaps because it encompasses a number of speech domains (compared to isolated features) it is able to detect those subtle differences we report. We originally thought differences between groups may be due to smoking and cigarette use, however we controlled for those and the differences remained.

How do your findings build on what we know about cannabis' link to the neural control of speech?

Data provide support to the approach that speech is sensitive to disturbance in the central nervous system. The exact neurological site of disturbance relating to speech is unclear and not the focus of this study, however, cannabis use appears to be linked with neuroanatomical alterations including smaller hippocampus and amygdala volumes, and gray and white matter density in the cerebellum and insular cortex with greater alterations linked with heavier use and an earlier age of onset of use. Attenuated white matter connectivity is also linked with earlier age of onset of cannabis use. These brain regions, in particular the cerebellum, play an important role in speech motor control and timing.

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  1. N Christopher-Hayes et al., Hum Brain Mapp (2021). Online ahead of print. Available at: https://bit.ly/38MmGgU

About the Author

Phoebe Harkin

Deputy Editor

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