Cannabis use may be associated with subtle long-lasting changes in speech, according to new exploratory research published in the journal Drug and Alcohol Dependence.
Cannabis appears to have long-lasting effects on motor function, including alterations in the way that people walk. Because speech is a complex motor skill involving the control of several muscles, researchers affiliated with The Neurophysiology of Human Movement Group set out to examine whether cannabis use was associated with alterations in speech timing, vocal control, and quality.
“Speech is sensitive to brain health. Changes that occur from drug use can lead to changes in behaviors and cognitive/motor acts, even in otherwise healthy adults. Professor Gabrielle Todd’s research group is focused on identifying changes in motor function that may occur from drug use,” explained study co-author Adam Vogel (@speechneuro), a professor and director of the Centre for Neuroscience of Speech at the University of Melbourne.
The study compared 31 adults with a history of recreational cannabis use to 40 adults with no history of drug use. To best reflect the typical cannabis-using population, the researchers recruited people who reported low-to-moderate cannabis use. The researchers also ensured that the cannabis users had no history of use of opioid drugs or illicit stimulants.
“We controlled for alcohol and cigarette smoking in our cohorts, so the differences we reported are not the result of those two aspects of the speaker,” Vogel noted.
The participants completed five speech tasks: a one-minute unprepared monologue, a sustained vowel, repeating pa-ta-ka as quickly and clearly as possible for 10 seconds, saying the days of the week, and reading a phonetically balanced text known as “The Grandfather Passage.” Each task was recorded and objectively examined using acoustic analysis.
Vogel and his colleagues found that cannabis users tended to exhibit reduced vocal quality in the form of decreased vocal intensity and increased vocal effort when reading “The Grandfather Passage.”
“There may be changes in neurological function resulting from prolonged use of cannabis and these may manifest in subtle alterations to speech. These changes are likely not detectable to the human ear, but require specialized methods for identification of the small but potentially genuine changes in performance,” Vogel told PsyPost.
The researchers also found that cannabis users produced speech with greater variability in pause length and were less likely to maintain a constant intensity of vocalizations compared to non-users. But these differences were no longer significant after applying a statistical correction known as a false discovery rate adjustment, leaving it unclear as to whether or not cannabis impacts these features of speech.
Future research that utilizes a longitudinal design could help to pin down what effects cannabis has on speech production.
“Data for this study are derived from a single time point, that is, subjects were not followed over time. We are making assumptions that the differences we observed between groups (cannabis vs non-drug users) were the result of cannabis use and not something else we haven’t accounted for,” Vogel said.
The study, “Adults with a history of recreational cannabis use have altered speech production“, was authored by Adam P. Vogel, Verity Pearson-Dennett, Michelle Magee, Robert A. Wilcox, Adrian Esterman, Dominic Thewlis, Jason M. White, and Gabrielle Todd.