Short-duration judgment in young Indian subjects under 30 h constant wakefulness.

The present study aimed to investigate probability of a possible endogenous circadian rhythm in human cognitive attribute to estimate short intervals. Apparently healthy young males and females were selected for our study. Eight subjects prospectively produced the short-time intervals 10 s and 60 s at 2 hourly intervals in 30 h constant routine (CR) study conducted in spring (CR-1). The study was repeated again in autumn (CR-2) in the remaining eight subjects. The established circadian markers, namely serum cortisol, salivary melatonin levels and tympanic temperature were also measured either in CR-1 or CR-2. Oral temperature was measured simultaneously. Circadian rhythms were validated in serum cortisol, salivary melatonin, oral, and tympanic temperatures. Circadian rhythm in 60 s estimates was observed in a few subjects and in all males at group level in CR-1. The cognitive attribute to perceive short intervals vary as function of season. The results provide evidence in support of interaction among the interval, circadian and circannual timing systems in human.