Gouzoulis-Mayfrank E, Thelen B, Maier S, Heekeren K, Kovar K-A, Sass H, Spitzer M (2002) Effects of the hallucinogen psilocybin on covert orienting of visual attention in humans. Neuropsychobiology, 45: 205-212
Drug effects on visual attentional processes were measured in 32 health human volunteers (21 men, 11 women, ages 27-47, average age 34,2) by comparing baseline responses to a task assessing covert orienting of visual attention to responses made after drug administration. In this task, participants respond as quickly as possible on spotting the target by pressing a key. Targets are presented in boxes to the left or right of central fixation, and trials are either given accurate (valid) or inaccurate (invalid) cues by brightening one of the boxes prior to target presentation. Target then appear either 100 ms (short cue) or 800 ms (long cue) later. Response time was measured in a double-blind, placebo controlled between-subjects study wherein participants were assigned to one of the following conditions; placebo, 2 mg/kg MDE, 0.2 mg/kg psilocybin or methamphetamine (0.2 or 0.4 mg/kg). All participants were physicians or psychologists and were free of any significant physical or psychiatric illness, and reported no psychiatric illness in first-degree relatives. (Data drawn from this sample, or sub-samples of this sample, have been previously presented.) Drug effects on visual attention were assessed during estimated peak drug effects. All participants showed quicker responses to validly cued trials than falsely cued ones, and did better with longer time from cue to target appearance. Participants had slower response times after psilocybin and MDE, with the effect stronger after psilocybin than after MDE. Methamphetamine did not significantly alter response time (there was a trend for shorter response times). Participants given psilocybin, but not MDE, showed particularly low response time to invalidly cued targets and short-cue interval, suggesting a difficulty disengaging from previously attended stimuli. Only participants given psilocybin showed a failure of response inhibition after long cues for targets appearing to the right (right visual field), while participants given MDE or methamphetamine did not show a visual field effect. It would appear that MDE and psilocybin impair visual attention, but that psilocybin has a greater impact on visual attention and shows some visual field effects similar to those seen in some studies of people with schizophrenia.
[See also under psilocybin]