Adult calendar calculators in a psychiatric OPD: a report of two cases and comparative analysis of abilities.

Two case reports are presented of psychiatric patients discovered in an adult psychiatric OPD who were proficient calendar calculators. Both were found to have similarities in history, clinical presentation, and symptomatology, Reaction times of both subjects on a set of 192 test dates were not random but were significantly predicted by the year and the month. In one subject (Tim), performance based on a visual stimulus differed little from that from an auditory stimulus. Although one subject was faster and more accurate, their response times significantly correlated. Statistical analysis revealed that this shared common variance resided in the month and year. It is hypothesized that they both employ their memory organized around a calendar-based system that entails keying off from December 1 of the test year.