| Authors: Rattigan JA, Mastropietro KF, Sur M, Umlauf A, Grelotti DJ, Fitzgerald RF, Grant I, Marcotte TD |
| Abstract:Objective:
Many individuals exhibit degradations in attention, executive functioning, and driving performance following acute use of ∆9-tetrahydrocannabinol (THC). Research on the combined effects of THC and high-intensity divided attention on driving performance is limited. The present study assessed pre- and post-smoking performance on a driving simulator before, during, and after a concurrent divided attention task.
Participants and Methods:
This study was part of a double-blind, placebo-controlled clinical trial. 128 participants (mean [SD] age = 30.8 [8.7] years; 67% male) completed driving simulations before and 30 minutes after smoking THC cigarettes ad libitum. A modified Surrogate Reference Task (mSuRT) was administered on an iPad to the right of the steering wheel while participants drove along a rural, traffic-free straightaway at 65MPH. Simulator performance was sampled before, during, and after the mSuRT to assess the effects of the absence, onset, and cessation of divided attention. Simulator outcomes included standard deviation of lateral position (i.e., swerving; SDLP) and time on the right shoulder of the road (TRSR). Carryover effects were operationalized as differences between pre-mSuRT and post-mSuRT simulator performance. Data analyses included linear mixed models (with maximum likelihood estimation) and pairwise comparisons (with Bonferroni corrections).
Results:
Median [IQR] THC concentrations were 0.0ng/mL [0.0, 1.9] and 35.0ng/mL [12.1, 60.9] at the start of the pre- and post-smoking drives, respectively. During the mSuRT, there were no differences between the two drives in vehicle speed, correct hits, or trial attempts (ps ≥ .067). During both drives, SDLP and TRSR increased with the onset of divided attention and subsequently decreased following its cessation (ps ≤ .004). However, carryover effects were observed; post-mSuRT SDLP and TRSR were greater than pre-mSuRT levels in both the pre- and post-smoking drives (ps ≤ .018). An interaction between smoking and divided attention was observed for SDLP (p = .008), such that divided attention onset and cessation induced smaller SDLP changes after smoking (ps ≤ .018). Of note, this conditional effect reflected the finding that post-smoking SDLP exceeded pre-smoking SDLP before and after the mSuRT (ps ≤ .004), but not during the mSuRT (p = .189). Additive main effects of smoking and divided attention were observed for TRSR (ps < .001); post-smoking TRSR was only greater than pre-smoking TRSR during the mSuRT (p = .018).
Conclusions:
Dividing attention depletes attentional resources, which may result in sustained, short-term detriments in driving performance. Carryover effects suggested increased swerving and time driving on the road shoulder may briefly persist after divided attention, regardless of THC use. Whereas alcohol generally magnifies divided attention’s effects on driving, the influence of THC is less clear. Smoking THC did not exacerbate the effects of actively divided attention on swerving, but THC induced greater swerving prior to task onset and attenuated the rate at which swerving reduced after divided attention cessation. Conversely, smoking THC contributed to a longer duration of time spent driving on the road shoulder during divided attention only. Although some feel more "aware" driving after cannabis use, our findings support deterring distracted and "high" driving, which may jointly affect one’s ability to drive safely, albeit in a complex manner. |