Abstract
In the case of a legal defence of drunkenness, it is common practice to call a psychiatrist to examine the accused and to give an opinion of his mental state at the time of the commission of the alleged offence. While clinical experience indicates that impairment may occur at relatively low concentrations of alcohol in the bloodstream, and that mental functions are not uniformly affected, there is surprisingly little experimental work to support this observation.
The present study was undertaken to determine the effects of a blood alcohol concentration of approximately 1.0 parts per 1,000 on mental functions. The subjects were eight non-psychotic males of average intelligence referred to the Forensic Services for mental examination. All were volunteers. The amount of alcohol in the bloodstream was measured by the Breathalyzer, and equivalent tests of general orientation and personal history; attention (digit span); abstract thinking (similarities test); learning efficiency (paired verbal associates) were administered before the intake of alcohol and when the blood alcohol concentration had reached 1.0 parts per 1,000. A test of retention was given, consisting of having the subjects identify and repeat the titles of TAT cards 24 hours after having described and titled them in an alcohol-free state and at the 1.0 level of blood alcohol respectively.
It was found that the experimental condition, i.e. a mean blood alcohol concentration of 1.0 parts per 1,000, had no effect upon the subjects' accuracy of information relating to personal identity and orientation in time and place.
The subjects' performances on the tests of attention, abstract thinking; and learning efficiency were adversely affected by the alcohol condition. Of the two retention measures, recognition and recall, only the latter was affected to a statistically significant degree.
A subsequent matching of a complete log of actual events occurring during the alcohol condition, with the subjects' recall of them 24 hours later, revealed vagueness; and of three subjects taken to the 2.0 parts per 1,000 level, two could not recall quite significant events occurring at higher concentration than 1.2 and 1.5 parts per 1,000. One of these subjects related the content of a conversation with the experimentor in a highly confabulatory manner.
The findings are taken to support the clinical observation that mental functions are not uniformly affected by alcohol, and that impairment can occur at relatively low concentrations of blood alcohol.