Six year old children are more likely to show signs of Attention Deficit Disorders if their mothers smoked 6 or more marijuana cigarettes per week. This was the conclusion after testing 126 children at the Department of Psychology, Carleton University, Canada. Fourteen of the children had mothers who admitted smoking between 1 and 6 ‘joints” per week and 19 had mothers who admitted smoking at least 6 marijuana joints per week during pregnancy. The testing was done using the Gordon Vigilance Task to examine ‘sustained attention.’ A series of single-digit numbers were shown on the computer screen at a rate of 1 per second. Each subject was asked to press a button whenever the number ‘1’ appeared after the number ‘9’ on the video screen. The children of heavy marijuana smokers made more errors of “omission’ in which they forgot to press the button when the ‘1’ appeared after the number ‘9’.

Although the results were not as strong as for those children whose mothers smoked cigarettes, the researchers stated in conclusion,

The data pertaining to maternal use of marijuana, are suggestive of an association between that drug and particular aspects of attentional behaviour – possibly sustained attention. Cognitive psychologists have frequently divided the attentional process into three sub-systems that perform different but interrelated functions. These include orienting toward sensory events, detecting signals to be focused on including information stored in memory and maintaining a vigilant state.” The present findings suggest that prenatal exposure to cigarettes and marijuana may be associated differentially with subsystems within the attentional process…. In addition, Discriminant Function Analysis revealed a dose-response relationship between prenatal marijuana use and a higher rating by the mothers on an impulsive scale.”