Long-tem time estimation is influenced by circadian phase

The adaptive significance of a putative time sense in humans remains unclea r as do the factors that underlie the capacity to gauge the passage of time . Here we show that the subjective assessment of relatively long durations varies systematically as a function of time of day. Specifically, the subje ctive clock ran relatively faster when the circadian oscillation of body te mperature was on the rise and relatively slower on the declining portion of the temperature curve. The overall result was a rather labile clock that, on average, ran slow relative to physical time. The results provide a glimp se into an underexplored aspect of how humans use their endogenous clocks i n the most fundamental way - to gauge the passage of time. (C) 2001 Elsevie r Science Inc. All rights reserved.