Reaction Time (RT) studies have reported psychomotor retardation in relation to Major Depression. However, the interpretation of RT data is constrained because individuals can adopt different speed-accuracy trade-off strategies. Inspection Time (IT) is an index that is not prone to speed-accuracy trade-offs, and measures the speed of early information processing. It is essential to locate the earliest information processing stage in which a breakdown occurs because any subsequent stage may as a consequence be impaired. IT may reflect the direct influence of the underlying mediating mechanism involving neurotransmitter activity. Participants who were medically diagnosed with psychiatric disorders were found to have longer ITs (slower speed of information processing) than healthy controls. Un-medicated patients, expected to have the most depleted level of neurotransmitter activity, were found to have the longest IT compared to medicated and healthy controls. Increased IT was also found during electroconvulsive treatment. The analyses shed some light on the underlying cognitive processes of psychiatric disorders.