The effects of cannabis on information-processing speed.

Despite extensive research on the effects of cannabis on cognitive and motor performance, studies administering computerised cognitive batteries and pencil-and-paper tests have not provided consistent results. Contributing factors are the broad range of tests used, together with a lack of sensitivity for assessing specific cognitive processes. This study for the first time assesses a very early cognitive process, information processing, that is sufficiently fundamental as to be immune from higher cognitive, motivational, and social processes. Information processes are thought to represent the basic building blocks of higher order cognitive processes. The inspection time (IT) task was used to investigate the effects of acute and subacute cannabis use on information processing in 22 heavy users, compared to 22 noncannabis-using controls. Findings indicate that users in the subacute state display significantly slowed information-processing speeds (longer ITs) compared to controls. Paradoxically, this deficit appears to be normalised whilst users are in the acute state. These results may be explained as a withdrawal effect, but may also be due to tolerance development as a result of long-term cannabis use. Furthermore, these results may assist in providing an explanation for the development of dependence with chronic cannabis users.