We report a ten year series of direct and indirect experiments to investigate the sensitivity of the McCollough Effect (ME) as an indicator of central neurotransmitter activity. With both pre- and post-adaptation single doses initial strength (IS) and duration of the ME relative to placebo were decreased by physostigmine and increased by hyoscine. A significant dose dependency was observed with oral hyoscine, but not with intramuscular hyoscine. Post adaptation exercise reduced IS linearly. Male introverts showed lower IS than male extraverts with monocular and binocular presentation, replicated with men, but not women, where ambiverts showed stronger effects than extraverts and introverts. Women showed a significant menstrual cycle effect with IS peaking premenstrually. In general, the ME was more sensitive than a control battery of standard psychomotor tests including saccadic eye-movements and CFF. The results are compatible with Error Correcting Device models for the ME.