Experiment 3: reversibility of attentional deficits in ex-cannabis users

The previous experiment established that the large processing negativity elicited by pitch irrelevant stimuli in long-term cannabis users performing a selective attention task increased with the duration of cannabis use. This was interpreted as a progressive impairment in the ability to focus attention and ignore complex irrelevant information, and suggested that longterm changes may occur as a result of cumulative exposure to cannabis.

This experiment was designed to assess the extent of reversibility of these changes with prolonged abstinence from cannabis use, and as such, examined the event-related potential (ERP) response in the same selective attention task of a group of long-term cannabis users who had ceased using cannabis. It was hypothesized that processing negativity (PN) to pitch irrelevant stimuli may gradually resolve over time as the duration of abstinence from cannabis increases.

Method

A power analysis based on the data of Experiment 2 determined an effect size greater than one standard deviation unit. With a sample of 32 ex-users there would be an 80% chance of detecting a difference between groups of 0.7 standard deviation units at an alpha level of 0.05 (two-tailed test).

Subjects

Subjects were recruited from the general community by advertising. The criteria for inclusion were to have used cannabis for at least 5 years and to have given up using cannabis within the past few years and at the very least 6 weeks prior to testing (this would allow most of the accumulated cannabinoids to be eliminated from the body).